Monitoring mosquitoes in urban Dar es Salaam: evaluation of resting boxes, window exit traps, CDC light traps, Ifakara tent traps and human landing catches

Malaria transmission risk in the city of Accra, Ghana: vector behavior and distribution

Background

Urban malaria transmission in sub-Saharan Africa is often underestimated, emphasizing the need for research on vector distribution, abundance, behavior, and infectivity in cities. Since 2003, urban malaria transmission has intensified. Monitoring Anophelespopulations is crucial for developing effective interventions. This study examined the biting and resting habits, distribution, abundance, and Plasmodiuminfection of malaria vectors in Accra.

Methods

Adult malaria vectors were collected using human landing catch (HLC) and Prokopack aspiration (PPK) at ten sites in Accra, categorized into five groups: sites with Irrigated Urban Farming (IUF), Lower Socioeconomic Status (LS), Middle Socioeconomic Status (MS), High Socioeconomic Status (HS), and Peri-urban (PU) areas. Biting patterns and entomological transmission indices of An. gambiae s.l. were assessed, Molecular methods were used to detect sporozoite infection, bloodmeal sources, vector species, and insecticide resistant mutation genes.

Results

A total of 41,747 mosquitoes were collected. Of these, 95.49% (39,863/41,747) were host-seeking collected through human landing catch (HLC), consisting of Anopheles (52.54%, 20,945/39,863), Culex(42.00%, 16,742/39,863), Aedes (3.74%, 1,491/39,863), and Mansonia (1.72%, 685/39,863). The remaining 4.51% (1,884/41,747) were resting mosquitoes collected using a Procopack aspirator, comprising Anopheles (31.26%, 589), Culex (57.21%, 1,078), and Aedes (11.52%, 217). Overall, the irrigated urban farming (IUF) site category recorded the highest abundance of An. gambiae s.l. (48.63%, 10,466/21,520), followed by the peri-urban (PU) site category (18.06%, 3,887/21,520), high socioeconomic (HS) site category (16.42%, 3,533/21,520), middle socioeconomic (MS) site category (13.74%, 2,956/21,520), and low socioeconomic (LS) site category (3.15%, 678/21,520) in both HLC and Procopack collections.Significantly higher mosquito biting activity was observed during the late evening (LE), the classical mosquito biting time, in both the rainy (71.45%, 11,337/15,865) and dry (72.21%, 3,658/5,066) seasons. Indoor An. gambiae s.l. had higher sporozoite infectivity (70.64%, 77/109) than outdoor mosquitoes (29.35%, 32/109) (χ2 = 6.78, P = 0.009). Tuba from the IUF site had the highest sporozoite infectivity (32.11%, 35/109), with higher indoor (24.77%, 27/109) than outdoor (7.34%, 8/109) rates.

Conclusion

Anopheles gambiae s.l. drives urban malaria transmission in Accra, with high human bloodmeal indices and sporozoite infectivity, especially indoors. Urban agriculture promotes vector proliferation. Targeted indoor control and management of breeding sites in IUF areas are essential to reduce transmission.

Application of circular statistics in temporal distribution of adult mosquitoes in Qingdao, Shandong Province, China, 2021-2023

BACKGROUND

Analyses of the temporal distribution of mosquitoes are presented in statistical charts, but it is difficult to prove in statistics whether differences in peak periods exist among different years or habitats. This study aimed to investigate the application of circular statistics in determining the peak period and a comparison of differences.

METHODS

Surveillance of adult mosquitoes was conducted twice a month by light traps in five different habitats from March to November for 3 years (2021-2023) in Qingdao, Shandong Province, China. The Kruskal-Wallis test was performed to determine the differences in mosquito density among different years and habitats. Circular statistics and line charts were employed to determine the peak period and a comparison of differences.

RESULTS

Among a total of 14,834 adult mosquitoes comprising five mosquito species from four genera, Culex pipiens pallens was dominant and accounted for 89.6% of the specimens identified. Aedes albopictus, Armigeres subalbatus, and Anopheles sinensis made up 5.7%, 4.2%, and 0.5%, respectively. Culex tritaeniorhynchus accounted for less than 0.1%. The mean mosquito density (females/trap night) for the trapping period was 10.3 in 2021, 5.6 in 2022, and 3.6 in 2023. Among five habitats, the highest mosquito density was 8.9 in livestock sheds, followed by 6.8 in parks, 5.9 in rural dwellings, 5.5 in urban dwellings, and 5.4 in hospitals. No statistically significant differences were found among different years (H = 1.96, d.f. 2, P = 0.376) and habitats (H = 0.45, d.f. 4, P = 0.978). Overall, the peak period of mosquito activity fell in the months from June to September. The peak period among 3 years differed significantly (F(2,7022) = 119.17, P < 0.01), but there were no statistically significant differences in peak period among different habitats (F(4,7020) = -159.09, P > 0.05).

CONCLUSION

Circular statistics could be effectively combined with statistical charts to elucidate the peak period of mosquitoes and determine the differences in statistics among different years and habitats. These findings will provide valuable information for mosquito control and public health management.

Comparison of standard and modified human landing catching techniques for blackfly collection

BACKGROUND

Human landing catches (HLCs) are required to collect blackflies for entomological evaluation to verify onchocerciasis elimination. However, there are ethical concerns regarding exposure of vector collectors to infectious blackflies and safer alternative methods are needed. This study evaluated a modified HLC technique where collectors wore coloured trousers (blue, black or blue-black), protecting them from bites during fly collection, and their performance was compared with the standard.

METHODS

The study was conducted in Makouopsap, Cameroon, in the Massangam health district for 4 months. Four collector pairs-one 'standard' (bare-legged) and three modified-were placed 50 m apart along known breeding sites on the Mbam and Nja Rivers. Collections were performed from 07:00 to 17:00 h, 4 d/month. Hourly rates of flies caught were analysed using a negative binomial generalised linear model to explore associations between flies caught and collection techniques and seasons.

RESULTS

Overall, 17 246 blackflies were caught. There was no significant statistical difference in the number of blackflies and parous flies caught between black trousers and the standard. Thus there is a strong indication that wearing black trousers is a viable non-inferior alternative to the standard HLC.

CONCLUSIONS

Further studies are needed to confirm generalisability in different ecozones and transmission environments and among different blackfly species.

Assessment of Culicidae collection methods for xenomonitoring lymphatic filariasis in malaria co-infection context in Burkina Faso

BACKGROUND

Entomological surveillance of lymphatic filariasis and malaria infections play an important role in the decision-making of national programs to control, or eliminate these both diseases. In areas where both diseases prevalence is low, a large number of mosquitoes need to be sampled to determine vectors infection rate. To do this, efficient mosquito collection methods must be used. This study is part in this framework, to assess appropriate mosquito collection methods for lymphatic filariasis xenomonitoring in a coexistence context with malaria in Burkina Faso.

METHODOLOGY/PRINCIPAL FINDINGS

Mosquito collections were performed between August and September 2018 in four villages (Koulpissi, Seiga, and Péribgan, Saptan), distributed in East and South-West health regions of Burkina Faso. Different collection methods were used: Human Landing Catches (HLC) executed indoor and outdoor, Window Exit-Trap, Double Net Trap (DNT) and Pyrethrum Spray Catches (PSC). Molecular analyses were performed to identify Anopheles gambiae s.l. sibling species and to detect Wuchereria bancrofti and Plasmodium falciparum infection in Anopheles mosquitoes. A total of 3 322 mosquitoes were collected among this, Anopheles gambiae s.l. was the vector caught in largest proportion (63.82%). An. gambiae s.l. sibling species molecular characterization showed that An. gambiae was the dominant specie in all villages. The Human Landing Catches (indoor and outdoor) collected the highest proportion of mosquitoes (between 61.5% and 82.79%). For the sampling vectors infected to W. bancrofti or P. falciparum, PSC, HLC and Window Exit-Trap were found the most effective collection methods.

CONCLUSIONS/SIGNIFICANCE

This study revealed that HLC indoor and outdoor remained the most effective collection method. Likewise, the results showed the probability to use Window Exit-Trap and PSC collection methods to sample Anopheles infected.

Mosquitoes, Lymphatic Filariasis, and Public Health: A Systematic Review of Anopheles and Aedes Surveillance Strategies

Lymphatic Filariasis (LF) affects over 120 million people in 72 countries, with sub-periodic filariasis common in the Pacific. Wuchereria bancrofti has three physiological races, each with a unique microfilarial periodicity, and each race is isolated to a specific geographical region. Sub-periodic W. bancrofti is transmitted by various Aedes mosquito species, with Aedes polynesiensis and Aedes samoanus being the primary vectors in Samoa. The Aedes scutellaris and Aedes kochi groups are also important vectors in the South Pacific Islands. Anopheles species are important vectors of filariasis in rural areas of Asia and Africa. The Anopheles gambiae complex, Anopheles funestus, and the Anopheles punctulatus group are the most important vectors of W. bancrofti. These vectors exhibit indoor nocturnal biting behaviour and breed in a variety of habitats, including freshwater, saltwater, and temporary water bodies. Effective vector surveillance is central to LF control and elimination programs. However, the traditional Human Landing Collection (HLC) method, while valuable, poses ethical concerns and risks to collectors. Therefore, this review critically analyses alternative trapping tools for Aedes and Anopheles vectors in LF-endemic regions. We looked at 14 research publications that discussed W. bancrofti vector trapping methods. Pyrethrum Spray Catches (PSC), one of the seven traps studied for Anopheles LF vectors, was revealed to be the second most effective strategy after HLC, successfully catching Anopheles vectors in Nigeria, Ghana, Togo, and Burkina Faso. The PSC method has several drawbacks, such as the likelihood of overlooking exophilic mosquitoes or underestimating Anopheles populations. However, exit traps offered hope for capturing exophilic mosquitoes. Anopheles populations could also be sampled using the Anopheles Gravid Trap (AGT). In contrast, the effectiveness of the Double Net Traps (DNT) and the CDC Light Trap (CDC LT) varied. Gravid mosquito traps like the OviArt Gravid Trap (AGT) were shown to be useful tools for identifying endophilic and exophilic vectors during the exploration of novel collection techniques. The Stealth trap (ST) was suggested for sampling Anopheles mosquitoes, although specimen damage may make it difficult to identify the species. Although it needs more confirmation, the Ifakara Tent Trap C design (ITT-C) showed potential for outdoor mosquito sampling in Tanzania. Furvela tent traps successfully captured a variety of Anopheles species and are appropriate for use in a variety of eco-epidemiological settings. By contrast, for Aedes LF vectors, no specific sampling tool was identified for Aedes niveus, necessitating further research and development. However, traps like the Duplex cone trap, Resting Bucket Trap (RB), and Sticky Resting Bucket trap (SRB) proved effective for sampling Aedes albopictus, offering potential alternatives to HLC. This review emphasises the value of looking into alternative trapping methods for Aedes and Anopheles vectors in the LF-endemic region. Further research is required to determine the efficacy of novel collection techniques in various contexts, even if PSC and AGT show promise for sampling Anopheles vectors. The identified traps, along with ongoing research, provide valuable contributions to vector surveillance efforts in LF-endemic regions, enabling LF control and elimination strategies to advance.

The Shockwè trap: a human-baited exposure-free device for surveillance and behaviour studies of anthropophilic vectors

Background: The human biting rate (MBR) and entomological inoculation rate (EIR) are common parameters routinely used to measure the risk of malaria transmission. Both parameters can be estimated using human landing catches (HLC). Although it is considered the gold-standard, HLC puts collectors at higher risk of infection with mosquito-transmitted pathogens. Methods: A novel exposure-free host-seeking mosquito electrocution trap, the Shockwè trap (SHK), was developed and its efficiency for monitoring mosquito community composition and abundance was compared with human landing catches (HLC) as the gold-standard. Field experiments were performed in Massavasse village, southern Mozambique. Simultaneous indoor and outdoor collections of nocturnal host-seeking mosquitoes were carried out using the SHK and HLC methods. The relative sampling efficiency of SHK was estimated as the ratio of the numbers of mosquitoes caught in SHK compared HLC. Proportionality and density-dependence between SHK and HLC catches were estimated by mean of Bayesian regression approaches. Results: A total of 69,758 and 27,359 host-seeking mosquitoes comprising nineteen species and four genera, were collected by HLC and SHK respectively. In general, SHK and HLC sampled similar numbers of mosquito species, with the exceptions of the least common species Aedes sudanensis, Ae. subargenteus, and Coquillettidia versicolor that were caught only by HLC. The relative sampling efficiency and proportionality between SHK and matched HLC catches varied greatly between species and collection site. However, all mosquitoes collected by SHK were unfed, confirming the Shockwè trap design's performance and reliability as a successful mosquito exposure free sampling approach. Conclusions: Results demonstrate that SHK is a safe and reliable human-exposure free device for monitoring the occurrence of a wide range of mosquito, including major malaria and arboviruses vector species. However, improvements are needed to increase its sampling efficiency for less abundant mosquito species.

CDC light traps underestimate the protective efficacy of an indoor spatial repellent against bites from wild Anopheles arabiensis mosquitoes in Tanzania

BACKGROUND

Methods for evaluating efficacy of core malaria interventions in experimental and operational settings are well established but gaps exist for spatial repellents (SR). The objective of this study was to compare three different techniques: (1) collection of blood-fed mosquitoes (feeding), (2) human landing catch (HLC), and (3) CDC light trap (CDC-LT) collections for measuring the indoor protective efficacy (PE) of the volatile pyrethroid SR product Mosquito Shield^™ METHODS: The PE of Mosquito Shield^™ against a wild population of pyrethroid-resistant Anopheles arabiensis mosquitoes was determined via feeding, HLC, or CDC-LT using four simultaneous 3 by 3 Latin squares (LS) run using 12 experimental huts in Tanzania. On any given night each technique was assigned to two huts with control and two huts with treatment. The LS were run twice over 18 nights to give a sample size of 72 replicates for each technique. Data were analysed by negative binomial regression.

RESULTS

The PE of Mosquito Shield^™ measured as feeding inhibition was 84% (95% confidence interval (CI) 58-94% [Incidence Rate Ratio (IRR) 0.16 (0.06-0.42), p < 0.001]; landing inhibition 77% [64-86%, (IRR 0.23 (0.14-0.36) p < 0.001]; and reduction in numbers collected by CDC-LT 30% (0-56%) [IRR 0.70 (0.44-1.0) p = 0.160]. Analysis of the agreement of the PE measured by each technique relative to HLC indicated no statistical difference in PE measured by feeding inhibition and landing inhibition [IRR 0.73 (0.25-2.12) p = 0.568], but a significant difference in PE measured by CDC-LT and landing inhibition [IRR 3.13 (1.57-6.26) p = 0.001].

CONCLUSION

HLC gave a similar estimate of PE of Mosquito Shield^™ against An. arabiensis mosquitoes when compared to measuring blood-feeding directly, while CDC-LT underestimated PE relative to the other techniques. The results of this study indicate that CDC-LT could not effectively estimate PE of the indoor spatial repellent in this setting. It is critical to first evaluate the use of CDC-LT (and other tools) in local settings prior to their use in entomological studies when evaluating the impact of indoor SR to ensure that they reflect the true PE of the intervention.

Which trap is best? Alternatives to outdoor human landing catches for malaria vector surveillance: a meta-analysis

BACKGROUND

Human landing catches (HLC) are an entomological collection technique in which humans are used as attractants to capture medically relevant host-seeking mosquitoes. The use of this method has been a topic of extensive debate for decades mainly due to ethical concerns. Many alternatives to HLC have been proposed; however, no quantitative review and meta-analysis comparing HLC to outdoor alternative trapping methods has been conducted.

METHODS

A total of 58 comparisons across 12 countries were identified. We conducted a meta-analysis comparing the standardized mean difference of Anopheles captured by HLC and alternative traps. To explain heterogeneity, three moderators were chosen for analysis: trap type, location of study, and species captured. A meta-regression was fit to understand how the linear combination of moderators helped in explaining heterogeneity. The possibility of biased results due to publication bias was also explored.

RESULTS

Random-effects meta-analysis showed no statistically significant difference in the mean difference of Anopheles collected. Moderator analysis was conducted to determine the effects of trap type, geographical location of study, and the species of Anopheles captured. On average, tent-based traps captured significantly more Anopheles than outdoor HLC (95% CI: [- .9065, - 0.0544]), alternative traps in Africa captured on average more mosquitoes than outdoor HLC (95% CI: [- 2.8750, - 0.0294]), and alternative traps overall captured significantly more Anopheles gambiae s.l. than outdoor HLC (95% CI: [- 4.4613, - 0.2473]) on average. Meta-regression showed that up to 55.77% of the total heterogeneity found can be explained by a linear combination of the three moderators and the interaction between trap type and species. Subset analysis on An. gambiae s.l. showed that light traps specifically captured on average more of this species than HLC (95% CI: [- 18.3751, - 1.0629]). Publication bias likely exists. With 59.65% of studies reporting p-values less than 0.025, we believe there is an over representation in the literature of results indicating that alternative traps are superior to outdoor HLC.

CONCLUSIONS

Currently, there is no consensus on a single "magic bullet" alternative to outdoor HLC. The diversity of many alternative trap comparisons restricts potential metrics for comparisons to outdoor HLC. Further standardization and specific question-driven trap evaluations that consider target vector species and the vector control landscape are needed to allow for robust meta-analyses with less heterogeneity and to develop data-driven decision-making tools for malaria vector surveillance and control.

Development and evaluation of an efficient and real-time monitoring system for the vector mosquitoes, Aedes albopictus and Culex quinquefasciatus

Background

The surveillance of vector mosquitoes is essential for prevention and control of mosquito-borne diseases. In this study, we developed an internet-based vector mosquito monitor, MS-300, and evaluated its efficiency for the capture of the important vector mosquitoes, Aedes albopictus and Culex quinquefasciatus, in laboratory and field trials.

Methodology/Principal findings

The linear sizes of adult Ae. albopictus and Cx. quinquefasciatus were measured and an infrared window was designed based on these data. A device to specifically attract these two species and automatically transmit the number of captured mosquitoes to the internet was developed. The efficiency of the device in capturing the two species was tested in laboratory, semi-field and open field trials. The efficiency results for MS-300 for catching and identifying Ae. albopictus in laboratory mosquito-net cages were 98.5% and 99.3%, and 95.8% and 98.6%, respectively, for Cx. quinquefasciatus. In a wire-gauze screened house in semi-field trials, the efficiencies of MS-300 baited with a lure in catching Ae. albopictus and Cx. quinquefasciatus were 54.2% and 51.3%, respectively, which were significantly higher than 4% and 4.2% without the lure. The real-time monitoring data revealed two daily activity peaks for Ae. albopictus (8:00–10:00 and 17:00–19:00), and one peak for Cx. quinquefasciatus (20:00–24:00). During a 98-day surveillance trial in the field, totals of 1,118 Ae. albopictus and 2,302 Cx. quinquefasciatus were captured by MS-300. There is a close correlation between the number of captured mosquitoes and the temperature in the field, and a positive correlation in the species composition of the captured samples among the mosquitoes using MS-300, BioGents Sentinel traps and human landing catches.

Conclusions/Significance

The data support the conclusion that MS-300 can specifically and efficiently capture Ae. albopictus and Cx. quinquefasciatus, and monitor their density automatically in real-time. Therefore, MS-300 has potential for use as a surveillance tool for prevention and control of vector mosquitoes.

A statistical calibration tool for methods used to sample outdoor-biting mosquitoes

Background

Improved methods for sampling outdoor-biting mosquitoes are urgently needed to improve surveillance of vector-borne diseases. Such tools could potentially replace the human landing catch (HLC), which, despite being the most direct option for measuring human exposures, raises significant ethical and logistical concerns. Several alternatives are under development, but detailed evaluation still requires common frameworks for calibration relative to HLC. The aim of this study was to develop and validate a statistical framework for predicting human-biting rates from different exposure-free alternatives.

Methods

We obtained mosquito abundance data (Anopheles arabiensis, Anopheles funestus and Culex spp.) from a year-long Tanzanian study comparing six outdoor traps [Suna Trap (SUN), BG Sentinel (BGS), M-Trap (MTR), M-Trap + CDC (MTRC), Ifakara Tent Trap-C (ITT-C) and Mosquito Magnet-X Trap (MMX)] and HLC. Generalised linear models were developed within a Bayesian framework to investigate associations between the traps and HLC, taking intra- and inter-specific density dependence into account. The best model was used to create a calibration tool for predicting HLC-equivalents.

Results

For An. arabiensis, SUN catches had the strongest correlation with HLC (R² = 19.4), followed by BGS (R² = 17.2) and MTRC (R² = 13.1) catches. The least correlated catch was MMX (R² = 2.5). For An. funestus, BGS had the strongest correlation with the HLC (R² = 53.4), followed by MTRC (R² = 37.4) and MTR (R² = 37.4). For Culex mosquitoes, the traps most highly correlated with the HLC were MTR (R² = 45.4) and MTRC (R² = 44.2). Density dependence, both between and within species, influenced the performance of only BGS traps. An interactive Shiny App calibration tool was developed for this and similar applications.

Conclusion

We successfully developed a calibration tool to assess the performance of different traps for assessing outdoor-biting risk, and established a valuable framework for estimating human exposures based on the trap catches. The performance of candidate traps varied between mosquito taxa; thus, there was no single optimum. Although all the traps tested underestimated the HLC-derived exposures, it was possible to mathematically define their representativeness of the true biting risk, with or without density dependence. The results of this study emphasise the need to aim for a consistent and representative sampling approach, as opposed to simply seeking traps that catch the most mosquitoes.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05403-7.

The Centres for Disease Control light trap (CDC-LT) and the human decoy trap (HDT) compared to the human landing catch (HLC) for measuring Anopheles biting in rural Tanzania

Background

Vector mosquito biting intensity is an important measure to understand malaria transmission. Human landing catch (HLC) is an effective but labour-intensive, expensive, and potentially hazardous entomological surveillance tool. The Centres for Disease Control light trap (CDC-LT) and the human decoy trap (HDT) are exposure-free alternatives. This study compared the CDC-LT and HDT against HLC for measuring Anopheles biting in rural Tanzania and assessed their suitability as HLC proxies.

Methods

Indoor mosquito surveys using HLC and CDC-LT and outdoor surveys using HLC and HDT were conducted in 2017 and in 2019 in Ulanga, Tanzania in 19 villages, with one trap/house/night. Species composition, sporozoite rates and density/trap/night were compared. Aggregating the data by village and month, the Bland–Altman approach was used to assess agreement between trap types.

Results

Overall, 66,807 Anopheles funestus and 14,606 Anopheles arabiensis adult females were caught with 6,013 CDC-LT, 339 indoor-HLC, 136 HDT and 195 outdoor-HLC collections. Indoors, CDC-LT caught fewer An. arabiensis (Adjusted rate ratio [Adj.RR] = 0.35, 95% confidence interval [CI]: 0.27–0.46, p < 0.001) and An. funestus (Adj.RR = 0.63, 95%CI: 0.51–0.79, p < 0.001) than HLC per trap/night. Outdoors, HDT caught fewer An. arabiensis (Adj.RR = 0.04, 95%CI: 0.01–0.14, p < 0.001) and An. funestus (Adj.RR = 0.10, 95%CI: 0.07–0.15, p < 0.001) than HLC. The bias and variability in number of mosquitoes caught by the different traps were dependent on mosquito densities. The relative efficacies of both CDC-LT and HDT in comparison to HLC declined with increased mosquito abundance. The variability in the ratios was substantial for low HLC counts and decreased as mosquito abundance increased. The numbers of sporozoite positive mosquitoes were low for all traps.

Conclusions

CDC-LT can be suitable for comparing mosquito populations between study arms or over time if accuracy in the absolute biting rate, compared to HLC, is not required. CDC-LT is useful for estimating sporozoite rates because large numbers of traps can be deployed to collect adequate mosquito samples. The present design of the HDT is not amenable for use in large-scale entomological surveys. Use of HLC remains important for estimating human exposure to mosquitoes as part of estimating the entomological inoculation rate (EIR).

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-022-04192-9.

Aedes aegypti abundance, larval indices and risk for dengue virus transmission in Kinondoni district, Tanzania

BACKGROUND

Tanzania has experienced periodic dengue outbreaks with increased incidence since 2010. However, there is limited information on vector dynamics and transmission risk in most parts of the country. This study was conducted to determine Aedes mosquito abundance, larval indices and dengue virus infection rate as risk indicators for DENV transmission in Kinondoni district, Dar es Salaam, Tanzania.

METHODS

A cross-sectional study was conducted in three wards of Kinondoni district in Tanzania between December 2019 and January 2020. In each ward, three streets were randomly selected for adult and immature mosquito sampling. The adult mosquitoes were collected using Mosquito Magnet traps, while mosquito larvae and pupae were inspected in water-holding containers in the selected household compounds. The detection of dengue virus (DENV) in female Aedes mosquitoes was done using a one-step reverse transcription-polymerase chain reaction (RT-PCR) method.

RESULTS

Of the 1416 adult female mosquitoes collected, Ae. aegypti accounted for 16.8% (n = 238). A total of 333 water-holding containers were inspected and 201 (60.4%) had at least an Aedes larvae or pupae. Water-holding containers supporting the breeding of Aedes larvae and pupae included discarded car tires, flowerpots and small and large plastic containers. The overall House Index, Container Index and Breteau Index were 55.1%, 60.4% and 114.2, respectively. None of the 763 female Aedes mosquitoes tested by RT-PCR was found to be infected with DENV.

CONCLUSION

The presence and abundance Ae. aegypti mosquitoes and the large proportion of water-holding containers infested with the mosquito larvae and pupae put residents of Kinondoni district at high risk of DENV transmission. Our findings emphasize the need for continuous mosquito vector surveillance and control to prevent the possibility of future DENV outbreaks in Tanzania.

Insights into factors sustaining persistence of high malaria transmission in forested areas of sub-Saharan Africa: the case of Mvoua, South Cameroon

BACKGROUND

In Mvoua, a village situated in a forested area of Cameroon, recent studies have reported high prevalence of Plasmodium falciparum infection among the population. In order to understand factors that can sustain such a high malaria transmission, we investigated the biology of Anopheles vectors and its susceptibility to insecticides, as well as long-lasting insecticidal net (LLIN) coverage, use and bio-efficacy.

METHODS

A longitudinal entomological survey was conducted from July 2018 to April 2019. Adult mosquitoes were collected using the human landing catch (HLC) method and identified using morphological and molecular techniques. Anopheles gambiae (s.l.) larvae were sampled from several stagnant water pools throughout the village and reared to generate F1 adults. The presence of P. falciparum circumsporozoite antigen was detected in the heads and thoraces of mosquitoes collected as adults using an enzyme-linked immunosorbent assay. The insecticide susceptibility status of the local An. gambiae (s.l.) F1 population to the pyrethroid insecticides deltamethrin 0.5% and permethrin 0.75% was determined using World Health Organization-tube bioassays, while the frequency of the knockdown resistance (kdr) mutation was determined by PCR. Coverage, use and physical integrity of LLINs were assessed in households, then cone assays were used to test for their bio-efficacy on both the reference insecticide-susceptible Kisumu strain and on field F1 An. gambiae (s.l.) RESULTS: In total, 110 Anopheles mosquitoes were collected, of which 59.1% were identified as Anopheles funestus (s.l.), 38.18% as An. gambiae (s.l.) and 2.72% as An. ziemanii. Anopheles funestus was the most abundant species except in the long rainy season, when An. gambiae (s.l.) predominated (65.8%). In the dry seasons, vectors were principally endophagous (76% of those collected indoors) while they tended to be exophagous (66% of those collected outdoors) in rainy seasons. High Plasmodium infection was observed in An. gambiae (s.l.) and An. funestus, with a circumsporozoitic rate of 14.29 and 10.77%, respectively. Anopheles gambiae (s.l.) was highly resistant to pyrethroid insecticides (mortality rates: 32% for permethrin and 5% for deltamethrin) and harbored the kdr-L1014F mutation at a high frequency (89.74%). Of the 80 households surveyed, only 47.69% had achieved universal coverage with LLNs. Around 70% of the LLINs sampled were in poor physical condition, with a proportionate hole index > 300. Of the ten LLNs tested, eight were effective against the An. gambiae reference insecticide-susceptible Kisumu strain, showing mortality rate of > 80%, while none of these LLINs were efficient against local An. gamabie (s.l.) populations (mortality rates < 11.5%).

CONCLUSION

A combination of elevated P. falciparum infection in Anopheles vector populations, insufficient coverage and loss of effectiveness of LLINs due to physical degradation, as well as high resistance to pyrethroid insecticides is responsible for the persistence of high malaria transmission in forested rural area of Mvoua, Cameroon.

The need for new vector control approaches targeting outdoor biting Anopheline malaria vector communities

Since the implementation of Roll Back Malaria, the widespread use of insecticide-treated nets (ITNs) and indoor residual spraying (IRS) is thought to have played a major part in the decrease in mortality and morbidity achieved in malaria-endemic regions. In the past decade, resistance to major classes of insecticides recommended for public health has spread across many malaria vector populations. Increasingly, malaria vectors are also showing changes in vector behaviour in response to current indoor chemical vector control interventions. Changes in the time of biting and proportion of indoor biting of major vectors, as well as changes in the species composition of mosquito communities threaten the progress made to control malaria transmission. Outdoor biting mosquito populations contribute to malaria transmission in many parts of sub-Saharan Africa and pose new challenges as they cannot be reliably monitored or controlled using conventional tools. Here, we review existing and novel approaches that may be used to target outdoor communities of malaria vectors. We conclude that scalable tools designed specifically for the control and monitoring of outdoor biting and resting malaria vectors with increasingly complex and dynamic responses to intensifying malaria control interventions are urgently needed. These are crucial for integrated vector management programmes designed to challenge current and future vector populations.

Culicidae-centric metabarcoding through targeted use of D2 ribosomal DNA primers

A practical limitation to many metabarcoding initiatives is that sampling methods tend to collect many non-target taxa, which become “amplicon noise” that can saturate Next Generation Sequencing results and lead to both financial and resource inefficiencies. An available molecular tool that can significantly decrease these non-target amplicons and decrease the need for pre-DNA-extraction sorting of bycatch is the design of PCR primers tailored to the taxa under investigation. We assessed whether the D2 extension segment of the 28S ribosomal operon can limit this shortcoming within the context of mosquito (Culicidae) monitoring. We designed PCR primers that are fully conserved across mosquitos and exclude from amplification most other taxa likely to be collected with current sampling apparatuses. We show that, given enough sequencing depth, D2 is an effective marker for the detection of mosquito sequences within mock genomic DNA pools. As few as 3,050 quality-filtered Illumina reads were able to recover all 17 species in a bulk pool containing as little as 0.2% of constituent DNA from single taxa. We also mixed these mosquito DNA pools with high concentrations of non-Culicidae bycatch DNA and show that the component mosquito species are generally still recoverable and faithful to their original relative frequencies. Finally, we show that there is little loss of fidelity in abundance parameters when pools from degraded DNA samples were sequenced using the D2 primers.

Evaluation of human-baited double net trap and human-odour-baited CDC light trap for outdoor host-seeking malaria vector surveillance in Kenya and Ethiopia

Background

Surveillance of outdoor host-seeking malaria vectors is crucial to monitor changes in vector biting behaviour and evaluate the impact of vector control interventions. Human landing catch (HLC) has been considered the most reliable and gold standard surveillance method to estimate human-biting rates. However, it is labour-intensive, and its use is facing an increasing ethical concern due to potential risk of exposure to infectious mosquito bites. Thus, alternative methods are required. This study was conducted to evaluate the performance of human-odour-baited CDC light trap (HBLT) and human-baited double net trap (HDNT) for outdoor host-seeking malaria vector surveillance in Kenya and Ethiopia.

Methods

The sampling efficiency of HBLT and HDNT was compared with CDC light trap and HLC using Latin Square Design in Ahero and Iguhu sites, western Kenya and Bulbul site, southwestern Ethiopia between November 2015 and December 2018. The differences in Anopheles mosquito density among the trapping methods were compared using generalized linear model.

Results

Overall, 16,963 female Anopheles mosquitoes comprising Anopheles gambiae sensu lato (s.l.), Anopheles funestus s.l., Anopheles pharoensis, Anopheles coustani and Anopheles squamosus were collected. PCR results (n = 552) showed that Anopheles arabiensis was the only member of An. gambiae s.l. in Ahero and Bulbul, while 15.7% An. arabiensis and 84.3% An. gambiae sensu stricto (s.s.) constituted An. gambiae s.l. in Iguhu. In Ahero, HBLT captured 2.23 times as many An. arabiensis and 2.11 times as many An. funestus as CDC light trap. In the same site, HDNT yielded 3.43 times more An. arabiensis and 3.24 times more An. funestus than HBLT. In Iguhu, the density of Anopheles mosquitoes did not vary between the traps (p > 0.05). In Bulbul, HBLT caught 2.19 times as many An. arabiensis as CDC light trap, while HDNT caught 6.53 times as many An. arabiensis as CDC light trap. The mean density of An. arabiensis did not vary between HDNT and HLC (p = 0.098), whereas the HLC yielded significantly higher density of An. arabiensis compared to HBLT and CDC light trap. There was a significant density-independent positive correlation between HDNT and HLC (r = 0.69).

Conclusion

This study revealed that both HBLT and HDNT caught higher density of malaria vectors than conventional CDC light trap. Moreover, HDNT yielded a similar vector density as HLC, suggesting that it could be an alternative tool to HLC for outdoor host-seeking malaria vector surveillance.

The mosquito electrocuting trap as an exposure-free method for measuring human-biting rates by Aedes mosquito vectors

BACKGROUND

Entomological monitoring of Aedes vectors has largely relied on surveillance of larvae, pupae and non-host-seeking adults, which have been poorly correlated with human disease incidence. Exposure to mosquito-borne diseases can be more directly estimated using human landing catches (HLC), although this method is not recommended for Aedes-borne arboviruses. We evaluated a new method previously tested with malaria vectors, the mosquito electrocuting trap (MET) as an exposure-free alternative for measuring landing rates of Aedes mosquitoes on people. Aims were to (i) compare the MET to the BG-sentinel (BGS) trap gold standard approach for sampling host-seeking Aedes vectors; and (ii) characterize the diel activity of Aedes vectors and their association with microclimatic conditions.

METHODS

The study was conducted over 12 days in Quinindé (Ecuador) in May 2017. Mosquito sampling stations were set up in the peridomestic area of four houses. On each day of sampling, each house was allocated either a MET or a BGS trap, which were rotated amongst the four houses daily in a Latin square design. Mosquito abundance and microclimatic conditions were recorded hourly at each sampling station between 7:00-19:00 h to assess variation between vector abundance, trapping methods, and environmental conditions. All Aedes aegypti females were tested for the presence of Zika (ZIKV), dengue (DENV) and chikungunya (CHIKV) viruses.

RESULTS

A higher number of Ae. aegypti females were found in MET than in BGS collections, although no statistically significant differences in mean Ae. aegypti abundance between trapping methods were found. Both trapping methods indicated female Ae. aegypti had bimodal patterns of host-seeking, being highest during early morning and late afternoon hours. Mean Ae. aegypti daily abundance was negatively associated with daily temperature. No infection by ZIKV, DENV or CHIKV was detected in any Aedes mosquitoes caught by either trapping method.

CONCLUSION

We conclude the MET performs at least as well as the BGS standard and offers the additional advantage of direct measurement of per capita human-biting rates. If detection of arboviruses can be confirmed in MET-collected Aedes in future studies, this surveillance method could provide a valuable tool for surveillance and prediction on human arboviral exposure risk.

Evaluation of mosquito electrocuting traps as a safe alternative to the human landing catch for measuring human exposure to malaria vectors in Burkina Faso

BACKGROUND

Measuring human exposure to mosquito bites is a crucial component of vector-borne disease surveillance. For malaria vectors, the human landing catch (HLC) remains the gold standard for direct estimation of exposure. This method, however, is controversial since participants risk exposure to potentially infected mosquito bites. Recently an exposure-free mosquito electrocuting trap (MET) was developed to provide a safer alternative to the HLC. Early prototypes of the MET performed well in Tanzania but have yet to be tested in West Africa, where malaria vector species composition, ecology and behaviour are different. The performance of the MET relative to HLC for characterizing mosquito vector population dynamics and biting behaviour in Burkina Faso was evaluated.

METHODS

A longitudinal study was initiated within 12 villages in Burkina Faso in October 2016. Host-seeking mosquitoes were sampled monthly using HLC and MET collections over 14 months. Collections were made at 4 households on each night, with METs deployed inside and outside at 2 houses, and HLC inside and outside at another two. Malaria vector abundance, species composition, sporozoite rate and location of biting (indoor versus outdoor) were recorded.

RESULTS

In total, 41,800 mosquitoes were collected over 324 sampling nights, with the major malaria vector being Anopheles gambiae sensu lato (s.l.) complex. Overall the MET caught fewer An. gambiae s.l. than the HLC (mean predicted number of 0.78 versus 1.82 indoors, and 1.05 versus 2.04 outdoors). However, MET collections gave a consistent representation of seasonal dynamics in vector populations, species composition, biting behaviour (location and time) and malaria infection rates relative to HLC. As the relative performance of the MET was somewhat higher in outdoor versus indoor settings, this trapping method slightly underestimated the proportion of bites preventable by LLINs compared to the HLC (MET = 82.08%; HLC = 87.19%).

CONCLUSIONS

The MET collected proportionately fewer mosquitoes than the HLC. However, estimates of An. gambiae s.l. density in METs were highly correlated with HLC. Thus, although less sensitive, the MET is a safer alternative than the HLC. Its use is recommended particularly for sampling vectors in outdoor environments where it is most sensitive.

A comparative assessment of adult mosquito trapping methods to estimate spatial patterns of abundance and community composition in southern Africa

Background

Assessing adult mosquito populations is an important component of disease surveillance programs and ecosystem health assessments. Inference from adult trapping datasets involves comparing populations across space and time, but comparisons based on different trapping methods may be biased if traps have different efficiencies or sample different subsets of the mosquito community.

Methods

We compared four widely-used trapping methods for adult mosquito data collection in Kruger National Park (KNP), South Africa: Centers for Disease Control miniature light trap (CDC), Biogents Sentinel trap (BG), Biogents gravid Aedes trap (GAT) and a net trap. We quantified how trap choice and sampling effort influence inferences on the regional distribution of mosquito abundance, richness and community composition.

Results

The CDC and net traps together collected 96% (47% and 49% individually) of the 955 female mosquitoes sampled and 100% (85% and 78% individually) of the 40 species or species complexes identified. The CDC and net trap also identified similar regional patterns of community composition. However, inference on the regional patterns of abundance differed between these traps because mosquito abundance in the net trap was influenced by variation in weather conditions. The BG and GAT traps collected significantly fewer mosquitoes, limiting regional comparisons of abundance and community composition.

Conclusions

This study represents the first systematic assessment of trapping methods in natural savanna ecosystems in southern Africa. We recommend the CDC trap or the net trap for future monitoring and surveillance programs.

Sampling Adult Populations of Anopheles Mosquitoes

For the control and elimination of malaria, information on the local vector dynamics is essential. This information provides guidance on appropriate and timely deployment of vector control tools and their subsequent success. The data on the dynamics of local mosquito populations can be collected using many different Anopheles sampling methods. Dependent on the objectives, resources, time, and local environment, different traps and methods can be chosen. This chapter describes the sampling of adult populations, focusing on the important preparatory stages and some of the widely used sampling methods. The trapping methods discussed in this chapter are the human landing catch, human-baited net trap, animal landing catch, animal-baited net trap, CDC miniature light trap, Biogents Suna trap, peripheral net collection, pyrethrum collection, exit/entry trap, and resting shelter. For optimal deployment in the field, a step-by-step description of the sampling methods is given.

Assessment of the Suna trap for sampling mosquitoes indoors and outdoors

BACKGROUND

Entomological monitoring is important for public health because it provides data on the distribution, abundance and host-seeking behaviour of disease vectors. Various methods for sampling mosquitoes exist, most of which are biased towards, or specifically target, certain portions of a mosquito population. This study assessed the Suna trap, an odour-baited trap for sampling host-seeking mosquitoes both indoors and outdoors.

METHODS

Two separate field experiments were conducted in villages in southern Malawi. The efficiency of the Suna trap in sampling mosquitoes was compared to that of the human landing catch (HLC) indoors and outdoors and the Centers for Disease, Control and Prevention Light Trap (CDC-LT) indoors. Potential competition between two Suna traps during simultaneous use of the traps indoors and outdoors was assessed by comparing mosquito catch sizes across three treatments: one trap indoors only; one trap outdoors only; and one trap indoors and one trap outdoors used simultaneously at the same house.

RESULTS

The efficiency of the Suna trap in sampling female anophelines was similar to that of HLC indoors (P = 0.271) and HLC outdoors (P = 0.125), but lower than that of CDC-LT indoors (P = 0.001). Anopheline catch sizes in the Suna trap used alone indoors were similar to indoor Suna trap catch sizes when another Suna trap was simultaneously present outdoors (P = 0.891). Similarly, catch sizes of female anophelines with the Suna trap outdoors were similar to those that were caught outdoors when another Suna trap was simultaneously present indoors (P = 0.731).

CONCLUSIONS

The efficiency of the Suna trap in sampling mosquitoes was equivalent to that of the HLC. Whereas the CDC-LT was more efficient in collecting female anophelines indoors, the use of this trap outdoors is limited given the requirement of setting it next to an occupied bed net. As demonstrated in this research, outdoor collections are also essential because they provide data on the relative contribution of outdoor biting to malaria transmission. Therefore, the Suna trap could serve as an alternative to the HLC and the CDC-LT, because it does not require the use of humans as natural baits, allows standardised sampling conditions across sampling points, and can be used outdoors. Furthermore, using two Suna traps simultaneously indoors and outdoors does not interfere with the sampling efficiency of either trap, which would save a considerable amount of time, energy, and resources compared to setting the traps indoors and then outdoors in two consecutive nights.

Bigoga J. The bionomics of the malaria vector Anopheles rufipes Gough, 1910 and its susceptibility to deltamethrin insecticide in North Cameroon

BACKGROUND

Following the recent discovery of the role of Anopheles rufipes Gough, 1910 in human malaria transmission in the northern savannah of Cameroon, we report here additional information on its feeding and resting habits and its susceptibility to the pyrethroid insecticide deltamethrin.

METHODS

From 2011 to 2015, mosquito samples were collected in 38 locations across Garoua, Mayo Oulo and Pitoa health districts in North Cameroon. Adult anophelines collected using outdoor clay pots, window exit traps and indoor spray catches were checked for feeding status, blood meal origin and Plasmodium circumsporozoite protein. The susceptibility of field-collected An. rufipes to deltamethrin was assessed using WHO standard procedures.

RESULTS

Of 9327 adult Anopheles collected in the 38 study sites, An. rufipes (6.5%) was overall the fifth most abundant malaria vector species following An. arabiensis (52.4%), An. funestus (s.l.) (20.8%), An. coluzzii (12.6%) and An. gambiae (6.8%). This species was found outdoors (51.2%) or entering houses (48.8%) in 35 suburban and rural locations, together with main vector species. Apart from human blood with index of 37%, An. rufipes also fed on animals including cows (52%), sheep (49%), pigs (16%), chickens (2%) and horses (1%). The overall parasite infection rate of this species was 0.4% based on the detection of P. falciparum circumsporozoite proteins in two of 517 specimens tested. Among the 21 An. rufipes populations assessed for deltamethrin susceptibility, seven populations were classified as "susceptible" (mortality ≥ 98%) , ten as "probable resistant" with a mortality range of 90-97% and four as "resistant" with a mortality range of 80-89%.

CONCLUSIONS

This study revealed changeable resting and feeding behaviour of An. rufipes, as well as further evidence on its ability to carry human malaria parasites in North Cameroon. Besides, this species is developing physiological resistance to deltamethrin insecticide which is used in treated nets and agriculture throughout the country, and should be regarded as one of potential targets for the control of residual malaria parasite transmission in Africa.

The Dark Side of Light Traps

Light-baited suction traps are one of the most widely used tools for vector surveillance. Their popularity stems from ease of use even in remote locations, range and abundance of species caught, and low cost. The availability of smaller, portable models, like the CDC miniature light trap, have further increased their ubiquity in entomological field studies. However, when researchers have looked, light trap collections are usually biased in ways that may affect data interpretation for epidemiological studies. If used alone, light traps may fail to collect important or infected vectors, and light traps are inefficient or ineffective when competing ambient light is present. In this article, we discuss these biases and limitations in terms of their effect on collection efficiency, population data, and pathogen detection. While light trap data certainly have a purpose, an over-reliance on light trapping risks drawing false conclusions about vector populations and vector-borne disease epidemiology. These concerns are especially troubling when light trap data are used to inform policy decisions meant to protect human and animal health. Particularly when a species' response to light is unknown or poorly characterized, light traps should be used in conjunction with supplemental sampling methods. Researchers conducting vector surveillance field studies should carefully consider their study design and objectives when deciding on a trapping method or methods, and specifically endeavor to understand the limitations of their data. Only then can researchers take advantage of the best attributes of light traps while avoiding their dark side.

Comparative evaluation of anopheline sampling methods in three localities in Indonesia

Background

The effectiveness of vector control efforts can vary based on the interventions used and local mosquito behaviour and adaptability. In many settings, biting patterns of Anopheles mosquitoes can shift in response to interventions targeting indoor-biting mosquitoes, often resulting in higher proportions of mosquitoes feeding outside or at times when people are not protected. These behaviourally resistant mosquitoes have been shown to sustain residual malaria transmission and limit control efforts. Therefore, it is important to accurately sample mosquitoes to understand their behaviour.

Methods

A variety of traps were evaluated in three geographically diverse sites in malaria-endemic Indonesia to investigate local mosquito feeding behaviour and determine effective traps for surveillance.

Results

Eight traps were evaluated in three sites: Canti village, Lampung, Kaliharjo village, Purworejo, and Saketa village, Halmahera, Indonesia, including the gold standard human landing collection (HLC) and a variety of traps targeting host-seeking and resting mosquitoes both indoors and outdoors. Trapping, using indoor and outdoor HLC, the Ifakara tent trap C, goat and human-occupied tents, resting pots and boxes, and CDC miniature light traps was conducted for 16 nights in two sites and 8 nights in a third site, using a Latin square design. Trap efficacy varied by site, with outdoor HLC yielding the highest catch rates in Canti and Kaliharjo and a goat-baited tent trap proving most effective in Saketa. In Canti village, anthropophilic Anopheles sundaicus were caught indoors and outdoors using HLCs, peaking in the early morning. In Kaliharjo, a variety of mosquitoes were caught, mostly outdoors throughout the night. HLC was ineffective in Saketa, the only site where a goat-baited tent trap was tested. This trap was effective in catching zoophilic vectors outdoors before midnight.

Conclusions

Different trapping methods were suitable for different species, likely reflecting differences in behaviour among species. The three villages, each located on a different island in the Indonesian archipelago, contained mosquito populations with unique behaviours. These data suggest that the effectiveness of specific vector monitoring and control measures may vary by location.

Electronic supplementary material

The online version of this article (10.1186/s12936-017-2161-9) contains supplementary material, which is available to authorized users.

Light-Emitting Diode (LED) Traps Improve the Light-Trapping of Anopheline Mosquitoes

Numerous advantages over the standard incandescent lamp favor the use of light-emitting diodes (LEDs) as an alternative and inexpensive light source for sampling medically important insects in surveillance studies. Previously published studies examined the response of mosquitoes to different wavelengths, but data on anopheline mosquito LED attraction are limited. Center for Disease Control and Prevention-type light traps were modified by replacing the standard incandescent lamp with 5-mm LEDs, one emitting at 520 nm (green) and the other at 470 nm (blue). To test the influence of moon luminosity on LED catches, the experiments were conducted during the four lunar phases during each month of the study period. A total of 1,845 specimens representing eight anopheline species were collected. Anopheles (Nyssorhynchus) evansae (35.2%) was the most frequently collected, followed by An. (Nys.) triannulatus (21.9%), An. (Nys.) goeldii (12.9%), and An. (Nys.) argyritarsis (11.5%). The green LED was the most attractive light source, accounting for 43.3% of the individuals collected, followed by the blue (31.8%) and control (24.9%) lights. The LED traps were significantly more attractive than the control, independent of the lunar phase. Light trapping of anopheline mosquitoes was more efficient when the standard incandescent lamp was replaced with LEDs, regardless of the moon phase. The efficiency of LEDs improves light trapping results, and it is suggested that the use of LEDs as an attractant for anopheline mosquitoes should be taken into consideration when sampling anopheline mosquitoes.

Host attraction and biting behaviour of Anopheles mosquitoes in South Halmahera, Indonesia

Background

Indonesia is home to a variety of malaria vectors whose specific bionomic traits remain largely uncharacterized. Species-specific behaviours, such as host feeding preferences, impact the dynamics of malaria transmission and the effectiveness of vector control interventions.

Methods

To examine species-specific host attraction and feeding behaviours, a Latin square design was used to compare Anopheles mosquitoes attracted to human, cow, and goat-baited tents. Anopheles mosquitoes were collected hourly from the inside walls of each baited tent. Species were morphologically and then molecularly identified using rDNA ITS2 sequences. The head and thorax of individual specimens were analysed for Plasmodium DNA using PCR. Bloodmeals were identified using a multiplex PCR.

Results

A total of 1024, 137, and 74 Anopheles were collected over 12 nights in cow, goat, and human-baited tents, respectively. The species were identified as Anopheles kochi, Anopheles farauti s.s., Anopheles hackeri, Anopheles hinesorum, Anopheles indefinitus, Anopheles punctulatus, Anopheles tessellatus, Anopheles vagus, and Anopheles vanus, many of which are known to transmit human malaria. Molecular analysis of blood meals revealed a high level of feeding on multiple host species in a single night. Anopheles kochi, An. indefinitus, and An. vanus were infected with Plasmodium vivax at rates comparable to primary malaria vectors.

Conclusions

The species distributions of Anopheles mosquitoes attracted to human, goat, and cow hosts were similar. Eight of nine sporozoite positive samples were captured with animal-baited traps, indicating that even predominantly zoophilic mosquitoes may be contributing to malaria transmission. Multiple host feeding and flexibility in blood feeding behaviour have important implications for malaria transmission, malaria control, and the effectiveness of intervention and monitoring methods, particularly those that target human-feeding vectors.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-017-1950-5) contains supplementary material, which is available to authorized users.

High entomological inoculation rate of malaria vectors in area of high coverage of interventions in southwest Ethiopia: Implication for residual malaria transmission

In Ethiopia, vector control is the principal strategy to reduce the burden of malaria. The entomological indicators of malaria transmission such as density, sporozoite rate and entomological inoculation rate (EIR) are parameters used to assess the impact of the interventions and the intensity of malaria transmission. The susceptibility of malaria vectors also determines the effectiveness of insecticide based vector control tools. Hence, the aim of the study was to assess the species composition, sporozoite rate and EIR, and insecticide susceptibility status of malaria vectors. 33 houses (18 for Centre for Disease Control and Prevention (CDC) light traps and 15 for exit traps) were randomly selected to sample Anopheles mosquitoes from October 2015 to May 2016. Plasmodium circum-sporozoite proteins (CSPs) of An. arabiensis and An. pharoensis were determined using Enzyme-Linked Immuno-Sorbent Assay (ELISA). Five Anopheles species were identified from CDC Light traps and exit traps. An. arabiensis (80.2%) was the predominant species, followed by An. pharoensis (18.5%). An. pretoriensis, An. tenebrosus and An. rhodesiensis were documented in small numbers. 1056 Anopheles mosquitoes were tested for CSPs. Of which nine (eight An. arabiensis and one An. pharoensis) were positive for CSPs with an overall CSP rate of 0.85% (95% CI: 0.3-1.4). Five Anopheles mosquitoes were positive for P. falciparum and four were positive for P.vivax_210. P. falciparum CSP rate of An. arabiensis was 0.46% (95% CI: 0.13-1.2) and it was 0.54% (95% CI: 0.01-2.9) for An. pharoensis. The overall EIR of An. arabiensis was 5.3 infectious bites per/person (ib/p)/eight months. An. arabiensis was resistant to dieldrin (mortality rate of 57%) and deltamethrin with mortality rates of 71% but was fully susceptible to propoxur and bendiocarb. Based on the EIR of An. arabiensis, indoor malaria transmission was high regardless of high coverage of indoor-based interventions. Finally, there was an indoor residual malaria transmission in a village of high coverage of bed nets and where the principal malaria vector is susceptibility to propoxur and bendiocarb; insecticides currently in use for indoor residual spraying. The continuing indoor transmission of malaria in such village implies the need for new tools to supplement the existing interventions and to reduce indoor malaria transmission.

MosqTent: An individual portable protective double-chamber mosquito trap for anthropophilic mosquitoes

Here, we describe the development of the MosqTent, an innovative double-chamber mosquito trap in which a human being attracts mosquitoes while is protected from being bitten within the inner chamber of the trap, while mosquitoes are lured to enter an outer chamber where they are trapped. The MosqTent previously collected an average of 3,000 anophelines/man-hour compared to 240 anophelines/man-hour for the human landing catch (HLC), thereby providing high numbers of human host–seeking mosquitoes while protecting the collector from mosquito bites. The MosqTent performed well by collecting a high number of specimens of Anophelesmarajoara, a local vector and anthropophilic mosquito species present in high density, but not so well in collecting An. darlingi, an anthropophilic mosquito species considered the main vector in Brazil but is present in low-density conditions in the area. The HLC showed a higher efficiency in collecting An. darlingi in these low-density conditions. The MosqTent is light (<1 kg), portable (comes as a bag with two handles), flexible (can be used with other attractants), adaptable (can be deployed in a variety of environmental settings and weather conditions), and it can be used in the intra-, peri-, and in the extradomicile. Also, the MosqTent collected similar portions of parous females and anthropophilic mosquito species and collects specimens suitable for downstream analysis. Further developments may include testing for other fabric colors, different mesh sizes and dimensions for other hematophagous insects and conditions, additional chemical mosquito attractants, and even the replacement of the human attractant in favor of other attractants. MosqTent modifications that would allow the trap to be applied as a vector control tool with killing action could also be explored.

Bio-efficacy of deltamethrin based durable wall lining against wild populations of Anopheles gambiae s.l. in Northern Tanzania

Background

Indoor residual spraying (IRS) is one of the preferred tools used for control of malaria in many settings in the world. However, this control tool still faces challenges that include lack of long lasting active ingredient, limited number of well-trained personal, and need of repeated treatment which increases operational costs and reduces acceptability by residents. As a result there is need to develop and validate other methods which can complement the existing controls. The current study compared the bio-efficacy of durable wall lining (DL) (treated with deltamethrin 265 mg/m²) and IRS (with deltamethrin 5% WP at 20 mg/m²) on indoor mosquitoes densities and biting behaviour of mosquitoes in comparison with control houses without either DL or IRS.

Methods

A study with two treatment arms and a control was conducted in Magugu ward, Northern Tanzania. Overall, a total of 60 houses were selected for the study with 20 houses per treatment arm and control. From each arm and control five houses were selected for mosquitoes trapping. Mosquitoes were sampled from 18:00 to 07:00 hourly every month for a period of 6 months. Mosquitoes were sampled using CDC miniature light traps.

Results

A total of 14,400 female wild mosquitoes were used for contact bioassays in the control arm. 20 houses were sprayed, additionally walls of 20 houses were installed with wall liners, and walls of 20 unsprayed houses were used as control. Also, a total of 946 mosquitoes were sampled with traps in 60 houses during the hourly sampling for 6 months. A total of 3000 unfed females of An. gambiae s.l. wild population raised from larvae were collected from natural habitats in the same village for bioassays. The decline in indoor mosquitoes densities observed in this study did not lead to a shift in the biting cycles (P = 0.712). The number of mosquitoes caught indoors in houses with DL and IRS was significantly lower (P < 0.001) compared to control houses. When the comparisons were done between DL and IRS houses, the densities were significantly lower in DL houses compared to IRS houses (P = 0.021). In the DL installed houses, indoor mosquito density declined notably and sustained throughout the 6 months of the study. However, in those houses sprayed with deltamethrin 5% WP (PALI™5 WP), the density noted to start to increase within four months after spraying(do you mean to say that the densities declined up to 4 months post spraying and thereafter increased.

Conclusions

Considering the efficacy duration of DL against IRS with deltamethrin 5% WP on mosquito densities decline indoors. The results of this study suggest that DL is more effective in malaria control as its efficacy lasted more than that of IRS.

Comparison of two adult mosquito sampling methods with human landing catches in south-central Ethiopia

BACKGROUND

The human landing catch (HLC) is the standard reference method for measuring human exposure to mosquito bites. However, HLC is labour-intensive, exposes collectors to infectious mosquito bites and is subjected to collector bias. These necessitate local calibration and application of alternative methods. This study was undertaken to determine the relative sampling efficiency (RSE) of light traps with or without yeast-produced carbon dioxide bait vs. HLC in south-central Ethiopia.

METHODS

The experiment was conducted for 39 nights in a 3 × 3 Latin square randomized design with Anopheles arabiensis as the target species in the period between July and November 2014 in Edo Kontola village, south-central Ethiopia. Center for Disease Control and Prevention light trap catches (LTC) and yeast-generated carbon dioxide-baited light trap catches (CB-LTC) were each evaluated against HLC. The total nightly mosquito catches for each Anopheles species in either method was compared with HLC by Pearson correlation and simple linear regression analysis on log-transformed [log10(x + 1)] values. To test if the RSE of each alternative method was affected by mosquito density, the ratio of the number of mosquitoes in each method to the number of mosquitoes in HLC was plotted against the average mosquito abundance.

RESULTS

Overall, 7606 Anopheles females were collected by the three sampling methods. Among these 5228 (68.7%) were Anopheles ziemanni, 1153 (15.2%) An. arabiensis, 883 (11.6%) Anopheles funestus s.l., and 342 (4.5%) Anopheles pharoensis. HLC yielded 3392 (44.6%), CB-LTC 2150 (28.3%), and LTC 2064 (27.1%) Anopheles females. The RSEs of LTC and HLC for An. arabiensis were significantly correlated (p < 0.001) and density independent (p = 0.65). However, for outdoor collection of the same species, RSEs of LTC and CB-LTC were density dependent (p < 0.001). It was estimated that on average, indoor LTC and CB-LTC each caught 0.35 and 0.44 times that of indoor HLC for An. arabiensis respectively.

CONCLUSIONS

Results showed that HLC was the most efficient method for sampling An. arabiensis. LTC can be used for large-scale indoor An. arabiensis surveillance and monitoring when it is difficult to use HLC. CB-LTC does not substantially improve sampling of this major vector compared to LTC in this setting. Trial registration PACTR201411000882128 (retrospectively registered 8 September, 2014).

Patterns and determinants of malaria risk in urban and peri-urban areas of Blantyre, Malawi

Background

Although malaria disease in urban and peri-urban areas of sub-Saharan Africa is a growing concern, the epidemiologic patterns and drivers of transmission in these settings remain poorly understood. Factors associated with variation in malaria risk in urban and peri-urban areas were evaluated in this study.

Methods

A health facility-based, age and location-matched, case–control study of children 6–59 months of age was conducted in four urban and two peri-urban health facilities (HF) of Blantyre city, Malawi. Children with fever who sought care from the same HF were tested for malaria parasites by microscopy and PCR. Those testing positive or negative on both were defined as malaria cases or controls, respectively.

Results

A total of 187 cases and 286 controls were studied. In univariate analyses, higher level of education, possession of TV, and electricity in the house were negatively associated with malaria illness; these associations were similar in urban and peri-urban zones. Having travelled in the month before testing was strongly associated with clinical malaria, but only for participants living in the urban zones (OR = 5.1; 95% CI = 1.62, 15.8). Use of long-lasting insecticide nets (LLINs) the previous night was not associated with protection from malaria disease in any setting. In multivariate analyses, electricity in the house, travel within the previous month, and a higher level of education were all associated with decreased odds of malaria disease. Only a limited number of Anopheles mosquitoes were found by aspiration inside the households in the peri-urban areas, and none was collected from the urban households.

Conclusion

Travel was the main factor influencing the incidence of malaria illness among residents of urban Blantyre compared with peri-urban areas. Identification and understanding of key mobile demographic groups, their behaviours, and the pattern of parasite dispersal is critical to the design of more targeted interventions for the urban setting.

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Prospects, drawbacks and future needs of xenomonitoring for the endpoint evaluation of lymphatic filariasis elimination programs in Africa

Lymphatic filariasis (LF) is a debilitating disease caused by Wuchereria bancrofti, Brugia malayi and B. timori parasitic worms and transmitted by Culex, Anopheles, Aedes and Mansonia mosquitoes. Mass drug administration (MDA) to reduce the infection levels in the human population is the key component of LF elimination programs. However, the potential of the use of vector control is gaining recognition as a tool that can complement MDA. The method of monitoring the parasites in mosquito vectors is known as xenomonitoring. Monitoring of vectors for filarial larvae is an important assessment tool for LF elimination programs. Xenomonitoring has the advantage of giving a real-time estimate of disease, because the pre-patent period may take months after infection in humans. It is a non-invasive sensitive tool for assessing the presence of LF in endemic areas. The aim of this review is to discuss the prospects, challenges and needs of xenomonitoring as a public health tool, in the post-MDA evaluation activities of national LF elimination programs.

Spatio-temporal heterogeneity of malaria vectors in northern Zambia: implications for vector control

Background

Despite large reductions in malaria burden across Zambia, some regions continue to experience extremely high malaria transmission. In Nchelenge District, Luapula Province, northern Zambia, almost half the human population carries parasites. Intervention coverage has increased substantially over the past decade, but comprehensive district-wide entomological studies to guide delivery of vector control measures are lacking. This study describes the bionomics and spatio-temporal patterns of malaria vectors in Nchelenge over a two and a half year period, investigates what household factors are associated with high vector densities and determines why vector control may not have been effective in the past to better guide future control efforts.

Methods

Between April 2012 and September 2014, twenty-seven households from across Nchelenge District were randomly selected for monthly light trap collections of mosquitoes. Anopheline mosquitoes were identified morphologically and molecularly to species. Foraging rates were estimated and sporozoite rates were determined by circumsporozoite ELISAs to calculate annual entomological inoculation rates. Blood feeding rates and host preference were determined by PCR. Zero-inflated negative binomial models measured environmental and household factors associated with mosquito abundance at study households such as season, proximity to the lake, and use of vector control measures.

Results

The dominant species in Nchelenge was An. funestus (s.s.) with An. gambiae (s.s.) as a secondary vector. Both vectors were found together in large numbers across the district and the combined EIRs of the two vectors exceeded 80 infectious bites per person per annum. An. funestus household densities increased in the dry season whilst An. gambiae surged during the rains. Presence of insecticide treated nets (ITNs) and closed eaves in the houses were found to be associated with fewer numbers of An. gambiae but not An. funestus. There was no association with indoor residual spraying (IRS).

Conclusion

In Nchelenge, the co-existence of two highly anthropophagic vectors, present throughout the year, is likely to be driving the high malaria transmission evident in the district. The vectors here have been shown to be highly resistant to pyrethroids used for IRS during the study. Vector control interventions in this area would have to be multifaceted and district-wide for effective control of malaria.

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An improved mosquito electrocuting trap that safely reproduces epidemiologically relevant metrics of mosquito human-feeding behaviours as determined by human landing catch

Background

Reliable quantification of mosquito host—seeking behaviours is required to determine the efficacy of vector control methods. For malaria, the gold standard approach remains the risky human landing catch (HLC). Here compare the performance of an improved prototype of the mosquito electrocuting grid trap (MET) as a safer alternative with HLC for measuring malaria vector behaviour in Dar es Salaam, Tanzania.

Methods

Mosquito trapping was conducted at three sites within Dar es Salaam representing a range of urbanicity over a 7-month period (December 2012–July 2013, 168 sampling nights). At each site, sampling was conducted in a block of four houses, with two houses being allocated to HLC and the other to MET on each night of study. Sampling was conducted both indoors and outdoors (from 19:00 to 06:00 each night) at all houses, with trapping method (HLC and MET) being exchanged between pairs of houses at each site using a crossover design.

Results

The MET caught significantly more Anopheles gambiae sensu lato than the HLC, both indoors (RR [95 % confidence interval (CI)]) = 1.47 [1.23–1.76], P < 0.0001 and outdoors = 1.38 [1.14–1.67], P < 0.0001). The sensitivity of MET compared with HLC did not detectably change over the course of night for either An. gambiae s.l. (OR [CI]) = 1.01 [0.94–1.02], P = 0.27) or Culex spp. (OR [CI]) = 0.99 [0.99–1.0], P = 0.17) indoors and declined only slightly outdoors: An. gambiae s.l. (OR [CI]) = 0.92 [0.86–0.99], P = 0.04), and Culex spp. (OR [CI]) = 0.99 [0.98–0.99], P = 0.03). MET-based estimates of the proportions of mosquitoes caught indoors (P_i) or during sleeping hours (P_fl), as well as the proportion of human exposure to bites that would otherwise occurs indoors (π_i), were statistically indistinguishable from those based on HLC for An. gambiae s.l. (P = 0.43, 0.07 and 0.48, respectively) and Culex spp. (P = 0.76, 0.24 and 0.55, respectively).

Conclusions

This improved MET prototype is highly sensitive tool that accurately quantifies epidemiologically-relevant metrics of mosquito biting densities, behaviours and human exposure distribution.

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The epidemiology of residual Plasmodium falciparum malaria transmission and infection burden in an African city with high coverage of multiple vector control measures

Background

In the Tanzanian city of Dar es Salaam, high coverage of long-lasting insecticidal nets (LLINs), larvicide application (LA) and mosquito-proofed housing, was complemented with improved access to artemisinin-based combination therapy and rapid diagnostic tests by the end of 2012.

Methods

Three rounds of city-wide, cluster-sampled cross-sectional surveys of malaria parasite infection status, spanning 2010 to 2012, were complemented by two series of high-resolution, longitudinal surveys of vector density.

Results

Larvicide application using a granule formulation of Bacillus thuringiensis var. israelensis (Bti) had no effect upon either vector density (P = 0.820) or infection prevalence (P = 0.325) when managed by a private-sector contractor. Infection prevalence rebounded back to 13.8 % in 2010, compared with <2 % at the end of a previous Bti LA evaluation in 2008. Following transition to management by the Ministry of Health and Social Welfare (MoHSW), LA consistently reduced vector densities, first using the same Bti granule in early 2011 [odds ratio (OR) (95 % confidence interval (CI)) = 0.31 (0.14, 0.71), P = 0.0053] and then a pre-diluted aqueous suspension formulation from mid 2011 onwards [OR (95 % CI) = 0.15 (0.07, 0.30), P ≪ 0.000001]. While LA by MoHSW with the granule formulation was associated with reduced infection prevalence [OR (95 % CI) = 0.26 (0.12, 0.56), P = 0.00040], subsequent liquid suspension use, following a mass distribution to achieve universal coverage of LLINs that reduced vector density [OR (95 % CI) = 0.72 (0.51, 1.01), P = 0.057] and prevalence [OR (95 % CI) = 0.80 (0.69, 0.91), P = 0.0013], was not associated with further prevalence reduction (P = 0.836). Sleeping inside houses with complete window screens only reduced infection risk [OR (95 % CI) = 0.71 (0.62, 0.82), P = 0.0000036] if the evenings and mornings were also spent indoors. Furthermore, infection risk was only associated with local vector density [OR (95 % CI) = 6.99 (1.12, 43.7) at one vector mosquito per trap per night, P = 0.037] among the minority (14 %) of households lacking screening. Despite attenuation of malaria transmission and immunity, 88 % of infected residents experienced no recent fever, only 0.4 % of these afebrile cases had been treated for malaria, and prevalence remained high (9.9 %) at the end of the study.

Conclusions

While existing vector control interventions have dramatically attenuated malaria transmission in Dar es Salaam, further scale-up and additional measures to protect against mosquito bites outdoors are desirable. Accelerated elimination of chronic human infections persisting at high prevalence will require active, population-wide campaigns with curative drugs.

Electronic supplementary material

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Modification of the Suna Trap for Improved Survival and Quality of Mosquitoes in Support of Epidemiological Studies

Monitoring adult mosquito populations provides information that is critical for assessing risk of vector-borne disease transmission. The recently developed Suna trap was found to be a very effective trap when baited with an attractive odor blend. A modification of this trap was tested to improve its function as a tool for monitoring mosquito populations, including Anopheles coluzzii (An. gambiae sensu stricto molecular form M), Aedes aegypti, and Culex pipiens. The modified Suna trap (Suna-M) was altered by changing the position of the catch bag and the inclusion of a holding chamber in attempts to increase trapping efficacy and enhance the survival of mosquitoes. Each adaptation was tested in a dual-choice setup in a climate-controlled room against the original Suna trap and against 4 standard monitoring methods: the BG-sentinel (BGS), Centers for Disease Control and Prevention (CDC) light trap, Mosquito Magnet X (MM-X) trap, and human landing catch (HLC). No differences in trapping efficacy were observed between the original Suna trap and modified version; however, a version in which the funnel was extended with a box and supplemented with moistened cotton wool increased mosquito survival from 6.5% to 78.0% over 24 h. The HLC and BGS trap outperformed the Suna-M trap, whereas the MM-X and commonly used CDC light trap performed significantly less well than the Suna-M trap in the dual-choice setup. The performance of the Suna-M trap equaled the performance of the original Suna trap and could therefore be used for monitoring purposes. Although the HLC and BGS trap achieved higher catch sizes, the Suna trap has the advantage that it is standardized, does not place humans at risk, and is weather resistant. Field studies should be conducted to confirm that the Suna-M trap, baited with the odor blend, is an efficient and standardized tool to measure both indoor and outdoor disease transmission risk for a range of vector-borne diseases.

Applications and limitations of Centers for Disease Control and Prevention miniature light traps for measuring biting densities of African malaria vector populations: a pooled-analysis of 13 comparisons with human landing catches

Background

Measurement of densities of host-seeking malaria vectors is important for estimating levels of disease transmission, for appropriately allocating interventions, and for quantifying their impact. The gold standard for estimating mosquito—human contact rates is the human landing catch (HLC), where human volunteers catch mosquitoes that land on their exposed body parts. This approach necessitates exposure to potentially infectious mosquitoes, and is very labour intensive. There are several safer and less labour-intensive methods, with Centers for Disease Control light traps (LT) placed indoors near occupied bed nets being the most widely used.

Methods

This paper presents analyses of 13 studies with paired mosquito collections of LT and HLC to evaluate these methods for their consistency in sampling indoor-feeding mosquitoes belonging to the two major taxa of malaria vectors across Africa, the Anopheles gambiae sensu lato complex and the Anopheles funestus s.l. group. Both overall and study-specific sampling efficiencies of LT compared with HLC were computed, and regression methods that allow for the substantial variations in mosquito counts made by either method were used to test whether the sampling efficacy varies with mosquito density.

Results

Generally, LT were able to collect similar numbers of mosquitoes to the HLC indoors, although the relative sampling efficacy, measured by the ratio of LT:HLC varied considerably between studies. The overall best estimate for An. gambiae s.l. was 1.06 (95% credible interval: 0.68–1.64) and for An. funestus s.l. was 1.37 (0.70–2.68). Local calibration exercises are not reproducible, since only in a few studies did LT sample proportionally to HLC, and there was no geographical pattern or consistent trend with average density in the tendency for LT to either under- or over-sample.

Conclusions

LT are a crude tool at best, but are relatively easy to deploy on a large scale. Spatial and temporal variation in mosquito densities and human malaria transmission exposure span several orders of magnitude, compared to which the inconsistencies of LT are relatively small. LT, therefore, remain an invaluable and safe alternative to HLC for measuring indoor malaria transmission exposure in Africa.

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Impregnating hessian strips with the volatile pyrethroid transfluthrin prevents outdoor exposure to vectors of malaria and lymphatic filariasis in urban Dar es Salaam, Tanzania

Background

Semi-field trials using laboratory-reared Anopheles arabiensis have shown that, delivering the volatile pyrethroid transfluthrin by absorption into hessian strips, consistently provided > 99 % human protective efficacy against bites for 6 months without retreating. Here the impact of this approach upon human exposure to wild populations of vectors for both malaria and filariasis under full field conditions is assessed for the first time.

Methods

Transfluthrin-treated and untreated strips were placed around human volunteers conducting human landing catch in an outdoor environment in urban Dar es Salaam, where much human exposure to malaria and filariasis transmission occurs outdoors. The experiment was replicated 9 times at 16 outdoor catching stations in 4 distinct locations over 72 working nights between May and August 2012.

Results

Overall, the treated hessian strips conferred 99 % protection against An. gambiae (1 bite versus 159) and 92 % protection against Culex spp. (1478 bites versus 18,602). No decline in efficacy over the course of the study could be detected for the very sparse populations of An. gambiae (P = 0.32) and only a slow efficacy decline was observed for Culex spp. (P < 0.001), with protection remaining satisfactory over 3 months after strip treatment. Diversion of mosquitoes to unprotected humans in nearby houses was neither detected for An. gambiae (P = 0.152) nor for Culex spp. (Relative rate, [95 % CI] = 1.03, [0.95, 1.11], P = 0.499).

Conclusion

While this study raises more questions than it answers, the presented evidence of high protection over long periods suggest this technology may have potential for preventing outdoor transmission of malaria, lymphatic filariasis and other vector-borne pathogens.

No difference in the incidence of malaria in human-landing mosquito catch collectors and non-collectors in a Senegalese village with endemic malaria

Background

The human landing catches is the gold standard method used to study the vectors of malaria and to estimate their aggressiveness. However, this method has raised safety concerns due to a possible increased risk of malaria or other mosquito-borne diseases among the mosquito collectors. The aim of this study was to evaluate the incidence of malaria attacks among mosquito collectors and to compare these results with those of non-collectors in a Senegalese village.

Methods

From July 1990 to December 2011, a longitudinal malaria study involving mosquito collectors and non-collectors was performed in Dielmo village, Senegal. During the study period, 4 drugs were successively used to treat clinical malaria, and long-lasting insecticide-treated nets were offered to all villagers in July 2008. No malaria chemoprophylaxis was given to mosquito collectors. Incidence of uncomplicated clinical malaria and asymptomatic malaria infection were analyzed among these two groups while controlling for confounding factors associated with malaria risk in random effects negative binomial and logistic regression models, respectively.

Results

A total of 3,812 person-trimester observations of 199 adults at least 15 years of age were analyzed. Clinical malaria attacks accounted for 6.3% both in collectors and non-collectors, and asymptomatic malaria infections accounted for 21% and 20% in collectors and non-collectors, respectively. A non-significant lower risk of malaria was observed in the collector group in comparison with the non-collector group after adjusting for other risk factors of malaria and endemicity level (Clinical malaria: adjusted incidence rate ratio = 0.89; 95% confidence interval = 0.65-1.22; p= 0.47).

Conclusion

Being a mosquito collector in Dielmo was not significantly associated with an increased risk of malaria both under holoendemic, mesoendemic and hypoendemic conditions of malaria epidemiology. This result supports the view that HLC, the most accurate method for evaluating malaria transmission, may be used without health concerns in Dielmo.

Development of a New Mosquito Retention System for the BG-Malaria Trap To Reduce The Damage To Mosquitoes

The BG-Malaria trap was recently modified from the BioGents BG-Sentinel trap to collect Anopheles species, including Anopheles darlingi. However, the captured mosquitoes often lose their hind legs in the collector bag, making them difficult to identify. To develop a new collector system that is capable of maintaining the integrity of the mosquitoes collected in the BG-Malaria trap, we conducted a study in the municipalities of Belém (Pará State [PA]) and Porto Velho (Rondônia State [RO]), Brazil, using carbon dioxide-baited BG-Malaria traps with 4 different mosquito collector systems: standard, no bag, rigid short, and rigid long. Results indicated significant differences among the numbers of mosquitoes captured in the 4 different collectors (P < 0.05). Additionally, significantly fewer insects (P < 0.05) were damaged using the rigid short and rigid long collectors than by using the standard and no-bag collectors. We observed that the longer the insects remained in the collector, the higher the number of damaged insects; this effect was the greatest in the standard collector. The results of this study indicate that rigid long collectors were the best suited for use in the BG-Malaria trap.

Comparative assessment of diverse strategies for malaria vector population control based on measured rates at which mosquitoes utilize targeted resource subsets

Background

Eliminating malaria requires vector control interventions that dramatically reduce adult mosquito population densities and survival rates. Indoor applications of insecticidal nets and sprays are effective against an important minority of mosquito species that rely heavily upon human blood and habitations for survival. However, complementary approaches are needed to tackle a broader diversity of less human-specialized vectors by killing them at other resource targets.

Methods

Impacts of strategies that target insecticides to humans or animals can be rationalized in terms of biological coverage of blood resources, quantified as proportional coverage of all blood resources mosquito vectors utilize. Here, this concept is adapted to enable impact prediction for diverse vector control strategies based on measurements of utilization rates for any definable, targetable resource subset, even if that overall resource is not quantifiable.

Results

The usefulness of this approach is illustrated by deriving utilization rate estimates for various blood, resting site, and sugar resource subsets from existing entomological survey data. Reported impacts of insecticidal nets upon human-feeding vectors, and insecticide-treated livestock upon animal-feeding vectors, are approximately consistent with model predictions based on measured utilization rates for those human and animal blood resource subsets. Utilization rates for artificial sugar baits compare well with blood resources, and are consistent with observed impact when insecticide is added. While existing data was used to indirectly measure utilization rates for a variety of resting site subsets, by comparison with measured rates of blood resource utilization in the same settings, current techniques for capturing resting mosquitoes underestimate this quantity, and reliance upon complex models with numerous input parameters may limit the applicability of this approach.

Conclusions

While blood and sugar consumption can be readily quantified using existing methods for detecting natural markers or artificial tracers, improved techniques for labelling mosquitoes, or other arthropod pathogen vectors, will be required to assess vector control measures which target them when they utilize non-nutritional resources such as resting, oviposition, and mating sites.

Electronic supplementary material

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Is there an efficient trap or collection method for sampling Anopheles darlingi and other malaria vectors that can describe the essential parameters affecting transmission dynamics as effectively as human landing catches? - A Review

Distribution, abundance, feeding behaviour, host preference, parity status and human-biting and infection rates are among the medical entomological parameters evaluated when determining the vector capacity of mosquito species. To evaluate these parameters, mosquitoes must be collected using an appropriate method. Malaria is primarily transmitted by anthropophilic and synanthropic anophelines. Thus, collection methods must result in the identification of the anthropophilic species and efficiently evaluate the parameters involved in malaria transmission dynamics. Consequently, human landing catches would be the most appropriate method if not for their inherent risk. The choice of alternative anopheline collection methods, such as traps, must consider their effectiveness in reproducing the efficiency of human attraction. Collection methods lure mosquitoes by using a mixture of olfactory, visual and thermal cues. Here, we reviewed, classified and compared the efficiency of anopheline collection methods, with an emphasis on Neotropical anthropophilic species, especially Anopheles darlingi, in distinct malaria epidemiological conditions in Brazil.

Institutional evolution of a community-based programme for malaria control through larval source management in Dar es Salaam, United Republic of Tanzania

BACKGROUND

Community-based service delivery is vital to the effectiveness, affordability and sustainability of vector control generally, and to labour-intensive larval source management (LSM) programmes in particular.

CASE DESCRIPTION

The institutional evolution of a city-level, community-based LSM programme over 14 years in urban Dar es Salaam, Tanzania, illustrates how operational research projects can contribute to public health governance and to the establishment of sustainable service delivery programmes. Implementation, management and governance of this LSM programme is framed within a nested set of spatially-defined relationships between mosquitoes, residents, government and research institutions that build upward from neighbourhood to city and national scales.

DISCUSSION AND EVALUATION

The clear hierarchical structure associated with vertical, centralized management of decentralized, community-based service delivery, as well as increasingly clear differentiation of partner roles and responsibilities across several spatial scales, contributed to the evolution and subsequent growth of the programme.

CONCLUSIONS

The UMCP was based on the principle of an integrated operational research project that evolved over time as the City Council gradually took more responsibility for management. The central role of Dar es Salaam's City Council in coordinating LSM implementation enabled that flexibility; the institutionalization of management and planning in local administrative structures enhanced community-mobilization and funding possibilities at national and international levels. Ultimately, the high degree of program ownership by the City Council and three municipalities, coupled with catalytic donor funding and technical support from expert overseas partners have enabled establishment of a sustainable, internally-funded programme implemented by the National Ministry of Health and Social Welfare and supported by national research and training institutes.

A cost-effective, community-based, mosquito-trapping scheme that captures spatial and temporal heterogeneities of malaria transmission in rural Zambia

BACKGROUND

Monitoring mosquito population dynamics is essential to guide selection and evaluation of malaria vector control interventions but is typically implemented by mobile, centrally-managed teams who can only visit a limited number of locations frequently enough to capture longitudinal trends. Community-based (CB) mosquito trapping schemes for parallel, continuous monitoring of multiple locations are therefore required that are practical, affordable, effective, and reliable.

METHODS

A CB surveillance scheme, with a monthly sampling and reporting cycle for capturing malaria vectors, using Centers for Disease Control and Prevention light traps (LT) and Ifakara Tent Traps (ITT), were conducted by trained community health workers (CHW) in 14 clusters of households immediately surrounding health facilities in rural south-east Zambia. At the end of the study, a controlled quality assurance (QA) survey was conducted by a centrally supervised expert team using human landing catch (HLC), LT and ITT to evaluate accuracy of the CB trapping data. Active surveillance of malaria parasite infection rates amongst humans was conducted by CHWs in the same clusters to determine the epidemiological relevance of these CB entomological surveys.

RESULTS

CB-LT and CB-ITT exhibited relative sampling efficiencies of 50 and 7%, respectively, compared with QA surveys using the same traps. However, cost per sampling night was lowest for CB-LT ($13.6), followed closely by CB-ITT ($18.0), both of which were far less expensive than any QA survey (HLC: $138, LT: $289, ITT: $269). Cost per specimen of Anopheles funestus captured was lowest for CB-LT ($5.3), followed by potentially hazardous QA-HLC ($10.5) and then CB-ITT ($28.0), all of which were far more cost-effective than QA-LT ($141) and QA-ITT ($168). Time-trends of malaria diagnostic positivity (DP) followed those of An. funestus density with a one-month lag and the wide range of mean DP across clusters was closely associated with mean densities of An. funestus caught by CB-LT (P < 0.001).

CONCLUSIONS

CB trapping schemes appear to be far more affordable, epidemiologically relevant and cost-effective than centrally supervised trapping schemes and may well be applicable to enhance intervention trials and even enable routine programmatic monitoring of vector population dynamics on unprecedented national scales.

Estimating the annual entomological inoculation rate for Plasmodium falciparum transmitted by Anopheles gambiae s.l. using three sampling methods in three sites in Uganda

Background

The Plasmodium falciparum entomological inoculation rate (PfEIR) is a measure of exposure to infectious mosquitoes. It is usually interpreted as the number of P. falciparum infective bites received by an individual during a season or annually (aPfEIR). In an area of perennial transmission, the accuracy, precision and seasonal distribution (i.e., month by month) of aPfEIR were investigated. Data were drawn from three sites in Uganda with differing levels of transmission where falciparum malaria is transmitted mainly by Anopheles gambiae s.l. Estimates of aPfEIR derived from human-landing catches – the classic method for estimating biting rates – were compared with data from CDC light traps, and with catches of knock down and exit traps separately and combined.

Methods

Entomological surveillance was carried out over one year in 2011/12 in three settings: Jinja, a peri-urban area with low transmission; Kanungu, a rural area with moderate transmission; and Nagongera, Tororo District, a rural area with exceptionally high malaria transmission. Three sampling approaches were used from randomly selected houses with collections occurring once a month: human-landing collections (eight houses), CDC light traps (100 houses) and paired knock-down and exit traps each month (ten houses) for each setting. Up to 50 mosquitoes per month from each household were tested for sporozoites with P. falciparum by ELISA. Human biting rate (HBR) data were estimated month by month. P. falciparum Sporozoite rate (PfSR) for yearly and monthly data and confidence intervals were estimated using the binomial exact test. Monthly and yearly estimates of the HBR, the PfSR, and the PfEIR were estimated and compared.

Results

The estimated aPfEIR values using human-landing catch data were 3.8 (95% Confidence Intervals, CI 0-11.4) for Jinja, 26.6 (95% CI 7.6-49.4) for Kanungu, and 125 (95% CI 72.2-183.0) for Tororo. In general, the monthly PfEIR values showed strong seasonal signals with two peaks from May-June and October-December, although the precise timing of the peaks differed between sites. Estimated HBRs using human-landing catches were strongly correlated with those made using CDC light traps (r² = 0.67, p < 0.001), and with either knock-down catches (r² = 0.56, p < 0.001) and exit traps (r² = 0.82, p < 0.001) or the combined catches (r² = 0.73, p < 0.001). Using CDC light trap catch data, the PfSR in Tororo was strongly negatively correlated with monthly HBR (r² = 0.44, p = 0.01). In other sites, no patterns in the PfSR were discernible because either the number P. falciparum of sporozoite positive mosquitoes or the total number of mosquitoes caught was too low.

Conclusions

In these settings, light traps provide an alternative method for sampling indoor-resting mosquitoes to human-landing catches and have the advantage that they protect individuals from being bitten during collection, are easy to use and are not subject to collector bias. Knock-down catches and exit traps could also be used to replace human-landing catches. Although these are cheaper, they are subject to collector bias.

Design and testing of a novel, protective human-baited tent trap for the collection of anthropophilic disease vectors

Currently, there exists a deficit of safe, active trapping methods for the collection of host-seeking Anopheles and other disease-causing arthropod vectors. The gold-standard approach for mosquito collection is that of human landing catch (HLC), in which an individual exposes bare skin to possibly infected vectors. Here, we present the development of a new method for mosquito collection, the Infoscitex tent, which uses modern tent materials coupled with a novel trap design. This provides an efficacious, a non-labor-intensive, and a safe method for vector collection. In these initial studies, we found it collected an average of 27.7 Anopheles gambiae s.l. per trap per night in rural villages in southeastern Senegal, and 43.8 Culex group Vper trap per night in the semiurban town of Kedougou, Senegal. In direct comparisons with HLC, the tent was not statistically different for collection of Culex quinquefasciatus in crepuscular sampling, but was significantly less efficacious at trapping the highly motile dusk-biter Aedes aegypti. These studies suggest that the Infoscitex tent is a viable and safe alternative to HLC for Anopheles and Culex sampling in areas of high vector-borne disease infection risk.

Urban lymphatic filariasis in the metropolis of Dar es Salaam, Tanzania

Background

The last decades have seen a considerable increase in urbanization in Sub-Saharan Africa, and it is estimated that over 50% of the population will live in urban areas by 2040. Rapid growth of cities combined with limited economic resources often result in informal settlements and slums with favorable conditions for proliferation of vectors of lymphatic filariasis (LF). In Dar es Salaam, which has grown more than 30 times in population during the past 55 years (4.4 million inhabitants in 2012), previous surveys have indicated high prevalences of LF. This study investigated epidemiological aspects of LF in Dar es Salaam, as a background for planning and implementation of control.

Methods

Six sites with varying distance from the city center (3–30 km) and covering different population densities, socioeconomic characteristics, and water, sewerage and sanitary facilities were selected for the study. Pupils from one public primary school at each site were screened for circulating filarial antigen (CFA; marker of adult worm infection) and antibodies to Bm14 (marker of exposure to transmission). Community members were examined for CFA, microfilariae and chronic manifestations. Structured questionnaires were administered to pupils and heads of community households, and vector surveys were carried out in selected households.

Results

The study indicated that a tremendous decrease in the burden of LF infection had occurred, despite haphazard urbanisation. Contributing factors may be urban malaria control targeting Anopheles vectors, short survival time of the numerous Culex quinquefasciatus vectors in the urban environment, widespread use of bed nets and other mosquito proofing measures, and mass drug administration (MDA) in 2006 and 2007. Although the level of ongoing transmission was low, the burden of chronic LF disease was still high.

Conclusions

The development has so far been promising, but continued efforts are necessary to ensure elimination of LF as a public health problem. These will include improving the awareness of people about the role of mosquitoes in transmission of LF, more thorough implementation of environmental sanitation to reduce Cx. quinquefasciatus breeding, continued MDA to high-risk areas, and set-up of programmes for management of chronic LF disease.

Monitoring malaria vector control interventions: effectiveness of five different adult mosquito sampling methods

Long-term success of ongoing malaria control efforts based on mosquito bed nets (long-lasting insecticidal net) and indoor residual spraying is dependent on continuous monitoring of mosquito vectors, and thus on effective mosquito sampling tools. The objective of our study was to identify the most efficient mosquito sampling tool(s) for routine vector surveillance for malaria and lymphatic filariasis transmission in coastal Kenya. We evaluated relative efficacy of five collection methods--light traps associated with a person sleeping under a net, pyrethrum spray catches, Prokopack aspirator, clay pots, and urine-baited traps--in four villages representing three ecological settings along the south coast of Kenya. Of the five methods, light traps were the most efficient for collecting female Anopheles gambiae s.l. (Giles) (Diptera: Culicidae) and Anopheles funestus (Giles) (Diptera: Culicidae) mosquitoes, whereas the Prokopack aspirator was most efficient in collecting Culex quinquefasciatus (Say) (Diptera: Culicidae) and other culicines. With the low vector densities here, and across much of sub-Saharan Africa, wherever malaria interventions, long-lasting insecticidal nets, and/or indoor residual spraying are in place, the use of a single mosquito collection method will not be sufficient to achieve a representative sample of mosquito population structure. Light traps will remain a relevant tool for host-seeking mosquitoes, especially in the absence of human landing catches. For a fair representation of the indoor mosquito population, light traps will have to be supplemented with aspirator use, which has potential for routine monitoring of indoor resting mosquitoes, and can substitute the more labor-intensive and intrusive pyrethrum spray catches. There are still no sufficiently efficient mosquito collection methods for sampling outdoor mosquitoes, particularly those that are bloodfed.

Wuchereria bancrofti transmission pattern in southern Mali prior to and following the institution of mass drug administration

Background

The Global Programme to Eliminate Lymphatic Filariasis (GPELF) was launched in 2000 with the goal of stopping transmission of lymphatic filariasis (LF) through yearly mass drug administration (MDA). Although preliminary surveys of the human population in Mali suggested that Wuchereria bancrofti infection was highly endemic in the Sikasso district, baseline entomological data were required to confirm high levels of transmission prior to the selection of villages in this region for a study of the impact of MDA on transmission of LF by anopheline vectors.

Methods

W. bancrofti transmission was assessed in 2001 (pre-MDA) and 2002 (post-MDA) in the Central District of Sikasso in southern Mali by dissection of Anopheles mosquitoes caught using the human landing catch (HLC) method. The relative frequencies and molecular forms of An. gambiae complex were determined.

Results

The majority (86%) of the anopheline vectors captured were identified as An. gambiae complex, and these accounted for >90% of the entomological inoculation rate (EIR) during both years of the study. There was a dramatic decrease in the number of An. gambiae complex mosquitoes captured and in the An. gambiae complex infectivity rates following MDA, accounting for the observed decrease in EIR in 2002 (from 12.55 to 3.79 infective bites per person during the transmission season). An. funestus complex mosquitoes were responsible for a low level of transmission, which was similar during both years of the study (1.2 infective bites per person during the transmission season in 2001 and 1.03 in 2002).

Conclusions

Based on the entomological data from this study, the district of Sikasso was confirmed as an area of high W. bancrofti transmission. This led to the selection of this area for a multi-national study on the effects of MDA on LF transmission by anopheline vectors. Comparison of vector transmission parameters prior to and immediately following the first round of MDA demonstrated a significant decrease in overall transmission. Importantly, the dramatic variability in EIR over the transmission season suggests that the efficacy of MDA can be maximized by delivering drug at the beginning of the rainy season (just prior to the peak of transmission).

Standardizing operational vector sampling techniques for measuring malaria transmission intensity: evaluation of six mosquito collection methods in western Kenya

Background

Operational vector sampling methods lack standardization, making quantitative comparisons of malaria transmission across different settings difficult. Human landing catch (HLC) is considered the research gold standard for measuring human-mosquito contact, but is unsuitable for large-scale sampling. This study assessed mosquito catch rates of CDC light trap (CDC-LT), Ifakara tent trap (ITT), window exit trap (WET), pot resting trap (PRT), and box resting trap (BRT) relative to HLC in western Kenya to 1) identify appropriate methods for operational sampling in this region, and 2) contribute to a larger, overarching project comparing standardized evaluations of vector trapping methods across multiple countries.

Methods

Mosquitoes were collected from June to July 2009 in four districts: Rarieda, Kisumu West, Nyando, and Rachuonyo. In each district, all trapping methods were rotated 10 times through three houses in a 3 × 3 Latin Square design. Anophelines were identified by morphology and females classified as fed or non-fed. Anopheles gambiae s.l. were further identified as Anopheles gambiae s.s. or Anopheles arabiensis by PCR. Relative catch rates were estimated by negative binomial regression.

Results

When data were pooled across all four districts, catch rates (relative to HLC indoor) for An. gambiae s.l (95.6% An. arabiensis, 4.4% An. gambiae s.s) were high for HLC outdoor (RR = 1.01), CDC-LT (RR = 1.18), and ITT (RR = 1.39); moderate for WET (RR = 0.52) and PRT outdoor (RR = 0.32); and low for all remaining types of resting traps (PRT indoor, BRT indoor, and BRT outdoor; RR < 0.08 for all). For Anopheles funestus, relative catch rates were high for ITT (RR = 1.21); moderate for HLC outdoor (RR = 0.47), CDC-LT (RR = 0.69), and WET (RR = 0.49); and low for all resting traps (RR < 0.02 for all). At finer geographic scales, however, efficacy of each trap type varied from district to district.

Conclusions

ITT, CDC-LT, and WET appear to be effective methods for large-scale vector sampling in western Kenya. Ultimately, choice of collection method for operational surveillance should be driven by trap efficacy and scalability, rather than fine-scale precision with respect to HLC. When compared with recent, similar trap evaluations in Tanzania and Zambia, these data suggest that traps which actively lure host-seeking females will be most useful for surveillance in the face of declining vector densities.