Surveillance and detection of Haemaphysalis longicornis (Acari: Ixodidae) in protected areas from Georgia, USA

The invasion of the Asian longhorned tick, Haemaphysalis longicornis Neumann, into the United States poses a significant ecological, veterinarian, and public health threat. We conducted a comprehensive tick survey using standard tick flagging protocol for collection over 3 field seasons, March-August, and 56 surveyed sites to identify the presence of H. longicornis in the native ecosystem and prove its establishment according to USDA criteria. Of the total 56 state parks and wildlife management areas (WMA) surveyed, only one was found to be invaded by H. longicornis; detection of H. longicornis occurred at Buck Shoals Wildlife Management area in White County, GA. This site is maintained by the state of Georgia, has no agricultural animals present, and hosts a large white-tailed deer population. After the initial detection of H. longicornis in 2022, an additional field season occurred in 2023, where H. longicornis was confirmed as established based on USDA criteria. The increase in H. longicornis populations from 2021 to 2023 at Buck Shoals WMA points to the rapid spread of this tick within the environment. Our findings provide evidence of the rapid establishment of H. longicornis in the southern edge of suitability for this tick and within the native ecosystem beyond farmlands and private land.

Evidence of Ongoing Transmission of Zika Virus in Mérida, Mexico

Since the Zika virus (ZIKV) pandemic in 2015-2017, there has been a near absence of reported cases in the Americas outside of Brazil. However, the conditions for Aedes-borne transmission persist in Latin America, and the threat of ZIKV transmission is increasing as population immunity wanes. Mexico has reported only 70 cases of laboratory-confirmed ZIKV infection since 2020, with no cases recorded in the Yucatán peninsula. Here, we provide evidence of active ZIKV transmission, despite the absence of official case reports, in the city of Mérida, Mexico, the capital of the state of Yucatán. Capitalizing on an existing cohort, we detected cases in participants with symptoms consistent with flavivirus infection from 2021 to 2022. Serum samples from suspected cases were tested for ZIKV RNA by polymerase chain reaction or ZIKV-reactive IgM by ELISA. To provide more specific evidence of exposure, focus reduction neutralization tests were performed on ELISA-positive samples. Overall, we observed 25 suspected ZIKV infections for an estimated incidence of 2.8 symptomatic cases per 1,000 persons per year. Our findings emphasize the continuing threat of ZIKV transmission in the setting of decreased surveillance and reporting.

Building the vector in: construction practices and the invasion and persistence of Anopheles stephensi in Jigjiga, Ethiopia

Anopheles stephensi is a major vector of malaria in Asia and the Arabian Peninsula, and its recent invasion into Africa poses a major threat to malaria control and elimination efforts on the continent. The mosquito is well adapted to urban environments, and its presence in Africa could potentially lead to an increase in malaria transmission in cities. Most of the knowledge about An stephensi ecology in Africa has been generated from studies conducted during the rainy season, when vectors are most abundant. Here, we provide evidence from the peak of the dry season in the city of Jigjiga in Ethiopia, and report An stephensi immature stages infesting predominantly in water reservoirs made to support construction operations (ie, in construction sites or associated with brick-manufacturing businesses). Political and economic changes in Ethiopia (particularly the Somali Region) have fuelled an unprecedented construction boom since 2018 that, in our opinion, has been instrumental in the establishment, persistence, and propagation of An stephensi via the year-round availability of perennial larval habitats associated with construction. We argue that larval source management during the dry season might provide a unique opportunity for focused control of An stephensi in Jigjiga and similar areas.

Natural Aedes-Borne Virus Infection Detected in Male Adult Aedes aegypti (Diptera: Culicidae) Collected From Urban Settings in Mérida, Yucatán, México

Aedes-borne viruses (ABVs) such as dengue (DENV), chikungunya (CHIKV), and Zika (ZIKV) contribute significantly to the global burden of infectious diseases, disproportionately affecting disadvantaged populations from tropical and subtropical urban areas. ABVs can be transmitted from female mosquitoes to their progeny by vertical transmission via transovarial and/or trans-egg vertical transmission and contribute to the maintenance of infected-mosquito populations year-round in endemic regions. This study describes the natural infection rate of DENV, CHIKV, and ZIKV in field-caught male Aedes (Sergentomyia) aegypti (Linnaeus) mosquitoes from Mérida, Yucatán, México, as a proxy for the occurrence of vertical virus transmission. We used indoor sequential sampling with Prokopack aspirators to collect all mosquitoes inside houses from ABV hotspots areas. Collections were performed in a DENV and CHIKV post-epidemic phase and during a period of active ZIKV transmission. We individually RT-qPCR tested all indoor collected Ae. aegypti males (1,278) followed by Sanger sequencing analysis for final confirmation. A total of 6.7% male mosquitoes were positive for ABV (CHIKV = 5.7%; DENV = 0.9%; ZIKV = 0.1%) and came from 21.0% (30/143) houses infested with males. Most ABV-positive male mosquitoes were positive for CHIKV (84.8%). The distribution of ABV-positive Ae. aegypti males was aggregated in a few households, with two houses having 11 ABV-positive males each. We found a positive association between ABV-positive males and females per house. These findings suggested the occurrence of vertical arbovirus transmission within the mosquito populations in an ABV-endemic area and, a mechanism contributing to viral maintenance and virus re-emergence among humans in post-epidemic periods.

SARS-CoV-2 antibody prevalence in a pediatric cohort of unvaccinated children in Mérida, Yucatán, México

The prevalence of SARS-CoV-2 exposure in children during the global COVID-19 pandemic has been underestimated due to lack of testing and the relatively mild symptoms in adolescents. Understanding the exposure rates in the pediatric population is essential as children are the last to receive vaccines and can act as a source for SARS-CoV-2 mutants that may threaten vaccine escape. This cross-sectional study aims to quantify the prevalence of anti-SARS-CoV-2 serum antibodies in children in a major city in México in the Spring of 2021 and determine if there are any demographic or socioeconomic correlating factors. We obtained socioeconomic information and blood samples from 1,005 children from 50 neighborhood clusters in Mérida, Yucatán, México. We then tested the sera of these participants for anti-SARS-CoV-2 IgG and IgM antibodies using lateral flow immunochromatography. We found that 25.5% of children in our cohort were positive for anti-SARS-CoV-2 antibodies and there was no correlation between age and antibody prevalence. Children that lived with large families were statistically more likely to have antibodies against SARS-CoV-2. Spatial analyses identified two hotspots of high SARS-CoV-2 seroprevalence in the west of the city. These results indicate that a large urban population of unvaccinated children has been exposed to SARS-CoV-2 and that a major correlating factor was the number of people within the child's household with a minor correlation with particular geographical hotspots. There is also a larger population of children that may be susceptible to future infection upon easing of social distancing measures. These findings suggest that in future pandemic scenarios, limited public health resources can be best utilized on children living in large households in urban areas.

Efficacy of targeted indoor residual spraying with the pyrrole insecticide chlorfenapyr against pyrethroid-resistant Aedes aegypti

Background

There is an increased need to mitigate the emergence of insecticide resistance and incorporate new formulations and modes of application to control the urban vector Aedes aegypti. Most research and development of insecticide formulations for the control of Ae. aegypti has focused on their peridomestic use as truck-mounted ULV-sprays or thermal fogs despite the widespread knowledge that most resting Ae. aegypti are found indoors. A recent modification of indoor residual spraying (IRS), termed targeted IRS (TIRS) works by restricting applications to 1.5 m down to the floor and on key Ae. aegypti resting sites (under furniture). TIRS also opens the possibility of evaluating novel residual insecticide formulations currently being developed for malaria IRS.

Methods

We evaluated the residual efficacy of chlorfenapyr, formulated as Sylando 240SC, for 12 months on free-flying field-derived pyrethroid-resistant Ae. aegypti using a novel experimental house design in Merida, Mexico. On a monthly basis, 600 female Ae. aegypti were released into the houses and left indoors with access to sugar solution for 24 hours. After the exposure period, dead and alive mosquitoes were counted in houses treated with chlorfenapyr as well as untreated control houses to calculate 24-h mortality. An evaluation for these exposed cohorts of surviving mosquitoes was extended up to seven days under laboratory conditions to quantify “delayed mortality”.

Results

Mean acute (24-h) mortality of pyrethroid-resistant Ae. aegypti ranged 80–97% over 5 months, dropping below 30% after 7 months post-TIRS. If delayed mortality was considered (quantifying mosquito mortality up to 7 days after exposure), residual efficacy was above 90% for up to 7 months post-TIRS application. Generalized Additive Mixed Models quantified a residual efficacy of chlorfenapyr of 225 days (ca. 7.5 months).

Conclusions

Chlorfenapyr represents a new option for TIRS control of Ae. aegypti in urban areas, providing a highly-effective time of protection against indoor Ae. aegypti females of up to 7 months.

Vector control (VC) for managing Aedes aegypti and reducing transmission of Aedes-borne diseases is largely focused on peridomestic insecticide applications. However, the indoor resting behavior of Ae. aegypti and the acceleration of insecticide resistance owed to reduced modes of action have diminished the effectiveness of many VC tools. A targeted Indoor residual spraying (TIRS) modality in experimental housing units was employed to investigate the potential of chlorfenapyr, a pyrrole-class insecticide with known effectiveness to resistant mosquito species. This was the first investigation for chlorfenapyr use against locally resistant Ae. aegypti (Merida, Mexico) with this approach. Two treatment arms were investigated in the present study: TIRS and a control house where only water was sprayed. A comparison of entomological efficacy for TIRS applied to interior perimeter walls below 1.5 m with chlorfenapyr (formulated as Sylando 240SC) at 250 mg/m² over 12 months was assessed. TIRS chlorfenapyr treatments were highly efficacious and led to acute mortalities (after 24 exposure) above 80% up to 5 months; delayed mortalities (to Ae. aegypti) were monitored over seven days post exposures vs untreated controls. When delayed mortality was considered, residual efficacy of chlorfenapyr extended to 7 months. These data provide evidence that TIRS chlorfenapyr is an effective Aedes management tool that surpassed efficacy profiles for other TIRS insecticides that have been previously reported with this method. Further, Chlorfenapyr emerges as a novel addition to Ae. aegypti VC, and future studies should focus on its effectiveness and residual power as part of Phase II-III TIRS trials.

Protective effect of house screening against indoor Aedes aegypti in Mérida, Mexico: A cluster randomised controlled trial

OBJECTIVE

To evaluate the protective effect of house screening (HS) on indoor Aedes aegypti infestation, abundance and arboviral infection in Merida, Mexico.

METHODS

In 2019, we performed a cluster randomised controlled trial (6 control and 6 intervention areas: 100 households/area). Intervention clusters received permanently fixed fiberglass HS on all windows and doors. The study included two cross-sectional entomologic surveys, one baseline (dry season in May 2019) and one post-intervention (PI, rainy season between September and October 2019). The presence and number of indoor Aedes females and blood-fed females (indoor mosquito infestation) as well as arboviral infections with dengue (DENV) and Zika (ZIKV) viruses were evaluated in a subsample of 30 houses within each cluster.

RESULTS

HS houses had significantly lower risk for having Aedes aegypti female mosquitoes (odds ratio [OR] = 0.56, 95% CI 0.33-0.97, p = 0.04) and blood-fed females (OR = 0.53, 95% CI 0.28-0.97, p = 0.04) than unscreened households from the control arm. Compared to control houses, HS houses had significantly lower indoor Ae. aegypti abundance (rate ratio [RR] = 0.50, 95% CI 0.30-0.83, p = 0.01), blood-fed Ae. aegypti females (RR = 0.48, 95% CI 0.27-0.85, p = 0.01) and female Ae. aegypti positive for arboviruses (OR = 0.29, 95% CI 0.10-0.86, p = 0.02). The estimated intervention efficacy in reducing Ae. aegypti arbovirus infection was 71%.

CONCLUSIONS

These results provide evidence supporting the use of HS as an effective pesticide-free method to control house infestations with Aedes aegypti and reduce the transmission of Aedes-transmitted viruses such as DENV, chikungunya (CHIKV) and ZIKV.

The entomological impact of passive metofluthrin emanators against indoor Aedes aegypti: A randomized field trial

Background

In the absence of vaccines or drugs, insecticides are the mainstay of Aedes-borne disease control. Their utility is challenged by the slow deployment of resources, poor community compliance and inadequate household coverage. Novel application methods are required.

Methodology and principal findings

A 10% w/w metofluthrin “emanator” that passively disseminates insecticide from an impregnated net was evaluated in a randomized trial of 200 houses in Mexico. The devices were introduced at a rate of 1 per room and replaced at 3-week intervals. During each of 7 consecutive deployment cycles, indoor resting mosquitoes were sampled using aspirator collections. Assessments of mosquito landing behaviours were made in a subset of houses. Pre-treatment, there were no differences in Aedes aegypti indices between houses recruited to the control and treatment arms. Immediately after metofluthrin deployment, the entomological indices between the trial arms diverged. Averaged across the trial, there were significant reductions in Abundance Rate Ratios for total Ae. aegypti, female abundance and females that contained blood meals (2.5, 2.4 and 2.3-times fewer mosquitoes respectively; P<0.001). Average efficacy was 60.2% for total adults, 58.3% for females, and 57.2% for blood-fed females. The emanators also reduced mosquito landings by 90% from 12.5 to 1.2 per 10-minute sampling period (P<0.05). Homozygous forms of the pyrethroid resistant kdr alleles V410L, V1016L and F1534C were common in the target mosquito population; found in 39%, 24% and 95% of mosquitoes collected during the trial.

Conclusions/Significance

This is the first randomized control trial to evaluate the entomological impact of any volatile pyrethroid on urban Ae. aegypti. It demonstrates that volatile pyrethroids can have a sustained impact on Ae. aegypti population densities and human-vector contact indoors. These effects occur despite the presence of pyrethroid-resistant alleles in the target population. Formulations like these may have considerable utility for public health vector control responses.

Insecticidal control tools are heavily relied on for the control of mosquito-borne viruses such as dengue, chikungunya and Zika, but the logistics associated with conventional insecticide use (e.g. space sprays and residual formulations) are challenging. Considerable time and resources are required to treat household interiors; an impediment exacerbated by the difficulty in gaining entrance to households, and sometimes by limited compliance in the community. Another constraint to effective insecticide use is that many mosquito populations are resistant to the chemicals used. Volatile pyrethroids, exhibiting both lethal and behavioural effects on mosquitoes are available in formulations that release insecticides passively to the air, at room temperature. These may be suitable for deployment in houses with the aim of creating “bite-free” spaces. By removing the need for conventional application methods, these devices might be rapidly deployed with minimum disruption to households. This is the first large-scale, randomized control trial to evaluate the entomological impacts of volatile pyrethroids in an urban environment. Using metofluthrin as an example, we confirm that some formulations have a significant impact on Aedes aegypti densities and landing behaviour indoors. These effects occur despite the presence of pyrethroid-resistance alleles associated with conventional insecticide resistance.

The TIRS trial: protocol for a cluster randomized controlled trial assessing the efficacy of preventive targeted indoor residual spraying to reduce Aedes-borne viral illnesses in Merida, Mexico

BACKGROUND

Current urban vector control strategies have failed to contain dengue epidemics and to prevent the global expansion of Aedes-borne viruses (ABVs: dengue, chikungunya, Zika). Part of the challenge in sustaining effective ABV control emerges from the paucity of evidence regarding the epidemiological impact of any Aedes control method. A strategy for which there is limited epidemiological evidence is targeted indoor residual spraying (TIRS). TIRS is a modification of classic malaria indoor residual spraying that accounts for Aedes aegypti resting behavior by applying residual insecticides on exposed lower sections of walls (< 1.5 m), under furniture, and on dark surfaces.

METHODS/DESIGN

We are pursuing a two-arm, parallel, unblinded, cluster randomized controlled trial to quantify the overall efficacy of TIRS in reducing the burden of laboratory-confirmed ABV clinical disease (primary endpoint). The trial will be conducted in the city of Merida, Yucatan State, Mexico (population ~ 1million), where we will prospectively follow 4600 children aged 2-15 years at enrollment, distributed in 50 clusters of 5 × 5 city blocks each. Clusters will be randomly allocated (n = 25 per arm) using covariate-constrained randomization. A "fried egg" design will be followed, in which all blocks of the 5 × 5 cluster receive the intervention, but all sampling to evaluate the epidemiological and entomological endpoints will occur in the "yolk," the center 3 × 3 city blocks of each cluster. TIRS will be implemented as a preventive application (~ 1-2 months prior to the beginning of the ABV season). Active monitoring for symptomatic ABV illness will occur through weekly household visits and enhanced surveillance. Annual sero-surveys will be performed after each transmission season and entomological evaluations of Ae. aegypti indoor abundance and ABV infection rates monthly during the period of active surveillance. Epidemiological and entomological evaluation will continue for up to three transmission seasons.

DISCUSSION

The findings from this study will provide robust epidemiological evidence of the efficacy of TIRS in reducing ABV illness and infection. If efficacious, TIRS could drive a paradigm shift in Aedes control by considering Ae. aegypti behavior to guide residual insecticide applications and changing deployment to preemptive control (rather than in response to symptomatic cases), two major enhancements to existing practice.

TRIAL REGISTRATION

ClinicalTrials.gov NCT04343521 . Registered on 13 April 2020. The protocol also complies with the WHO International Clinical Trials Registry Platform (ICTRP) (Additional file 1).

PRIMARY SPONSOR

National Institutes of Health, National Institute of Allergy and Infectious Diseases (NIH/NIAID).

Transcontinental dispersal of Anopheles gambiae occurred from West African origin via serial founder events

The mosquito Anopheles gambiae s.s. is distributed across most of sub-Saharan Africa and is of major scientific and public health interest for being an African malaria vector. Here we present population genomic analyses of 111 specimens sampled from west to east Africa, including the first whole genome sequences from oceanic islands, the Comoros. Genetic distances between populations of A. gambiae are discordant with geographic distances but are consistent with a stepwise migration scenario in which the species increases its range from west to east Africa through consecutive founder events over the last ~200,000 years. Geological barriers like the Congo River basin and the East African rift seem to play an important role in shaping this process. Moreover, we find a high degree of genetic isolation of populations on the Comoros, confirming the potential of these islands as candidate sites for potential field trials of genetically engineered mosquitoes for malaria control.

Ethanol as a potential mosquito sample storage medium for RNA preservation

Sample storage for downstream RNA analysis can be challenging in some field settings, especially where access to cryogenic materials or refrigeration/freezer facilities are limited. This has limited RNA-based studies on African malaria vectors collected in the field. We evaluated RNA quality after storing mosquito samples in three different sample preservation media over a 4-week period. Storing mosquito specimens in cold (4°C) media significantly improved yields of intact RNA. Our results indicate commercially available products perform well in keeping RNA integrity as advertised. Moreover, absolute ethanol may be an economical alternative for sample preservation that can be utilized in some resource-limited settings.

A molecular analysis of sand fly blood meals in a visceral leishmaniasis endemic region of northwestern Ethiopia reveals a complex host-vector system

Background

Visceral leishmaniasis (VL, or “kala-azar”) is a major cause of disability and death, especially in East Africa. Its vectors, sand flies (Diptera: Psychodidae: Phlebotominae), are poorly controlled and guarded against in these regions, owing in part to a lack of understanding about their feeding behavior.

Methods

A total of 746 freshly fed female sand flies were collected in five population centers in Kafta Humera (northwestern Ethiopia), where VL is endemic. Flies were collected from habitats that ranged from inside houses to open fields, using light traps and sticky traps. Sources of sand fly blood meals were identified using enzyme-linked immunosorbent assays (ELISA) and DNA amplification with reverse-line blot analysis (PCR-RLB); 632 specimens were screened using ELISA, 408 of which had identifiable blood meals, and 114 were screened using PCR-RLB, 53 of which yielded identifications. Fly species determinations were based on morphology, and those specimens subjected to PCR-RLB were also screened for Leishmania parasites using conventional PCR to amplify the nuclear marker ITS1 (internal transcribed spacer 1) with Leishmania-specific primers.

Results

More than three-fourths of all sand flies collected were Phlebotomus orientalis, and the remaining portion was comprised of nine other species. Nearly two-thirds of P. orientalis specimens were collected at village peripheries. The most common blood source for all flies was donkey (33.9% of all identifications), followed by cow (24.2%), human (17.6%), dog (11.8%), and goat or sheep (8.6%); mixtures of blood meals from different sources were found in 28.2% of all flies screened. Unidentified blood meals, presumably from wildlife, not domestic animals, were significantly higher in farm fields. Leishmania parasites were not detected in any of the 114 flies screened, not surprising given an expected infection rate of 1–5 out of 1,000. Meals that included a mixture of human and cow blood were significantly more frequent relative to all cow meals than human blood meals were to non-cow meals, suggesting a zoopotentiative interaction between cows and humans in this system.

Conclusions

Habitat and host preferences of sand fly vectors in Kafta Humera confirmed the finding of previous reports that the main vector in the region, Phlebotomus orientalis, is a highly opportunistic feeder that prefers large animals and is most commonly found at village peripheries. These results were similar to those of a previous study conducted in a nearby region (Tahtay Adiabo), except for the role of cattle on the prevalence of human blood meals. Preliminary examinations of blood meal data from different settings point to the need for additional surveys and field experiments to understand the role of livestock on biting risks.

Studies on the behaviour and control of phlebotomine sandflies using experimental houses

Programmes for the control of phlebotomine sandflies (Diptera: Psychodidae), the vectors of leishmaniases, mainly target adults because larval breeding sites are generally unknown or inaccessible. To determine how blood-questing sandfly females enter homes and to develop means for their control, an experimental house (EH) was constructed in a village endemic for cutaneous leishmaniasis. Initially, carbon dioxide (CO₂ )-baited suction traps were installed inside the EH to attract and capture sandflies. For other experiments, the windows of the EH were fitted with CO₂ -baited window entrance traps (WETs) that allow each window to be considered as a separate unit. The majority of captures inside the EH and in WETs consisted of Phlebotomus sergenti, a species that enters inhabited houses relatively infrequently. Analyses of collections in WETs and in sticky traps on external walls showed that sandflies entered windows having landed previously on the wall below or either side of the window. Shelves constructed below windows significantly reduced the numbers of sandflies that entered both the EH and inhabited houses. The lining of internal walls with insecticide-impregnated fabric significantly increased mortality rates of sandflies captured inside the EH. To reduce the biting burden imposed by phlebotomine sandflies, several control measures must be integrated and sustained.

Optimization of loop-mediated isothermal amplification (LAMP) assays for the detection of Leishmania DNA in human blood samples

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Three systems of loop-mediated isothermal amplification (LAMP) were developed for diagnosing leishmaniasis.

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The green nucleic acid stain, SYTO-16 was adapted for monitoring the reactions in real-time.

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The LAMP assays proved highly sensitive detecting >100Fg DNA/reaction.

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Leishmania DNA was detected in a significant number of asymptomatic individuals living in endemic areas.

Visceral leishmaniasis (VL), one of the most important neglected tropical diseases, is caused by Leishmania donovani eukaryotic protozoan parasite of the genus Leishmania, the disease is prevalent mainly in the Indian sub-continent, East Africa and Brazil. VL can be diagnosed by PCR amplifying ITS1 and/or kDNA genes. The current study involved the optimization of Loop-mediated isothermal amplification (LAMP) for the detection of Leishmania DNA in human blood or tissue samples. Three LAMP systems were developed; in two of those the primers were designed based on shared regions of the ITS1 gene among different Leishmania species, while the primers for the third LAMP system were derived from a newly identified repeated region in the Leishmania genome. The LAMP tests were shown to be sufficiently sensitive to detect 0.1 pg of DNA from most Leishmania species. The green nucleic acid stain SYTO16, was used here for the first time to allow real-time monitoring of LAMP amplification. The advantage of real time-LAMP using SYTO 16 over end-point LAMP product detection is discussed. The efficacy of the real time-LAMP tests for detecting Leishmania DNA in dried blood samples from volunteers living in endemic areas, was compared with that of qRT-kDNA PCR.

Risk factors of visceral leishmaniasis: a case control study in north-western Ethiopia

Background

Visceral leishmaniasis (VL, also called ‘’kala-azar”), is a life threatening neglected tropical infectious disease which mainly affects the poorest of the poor. VL is prevalent in Ethiopia particularly in the northwest of the country. Understanding the risk factors of VL infection helps in its prevention and control. The aim of the present study was to identify the factors associated with VL.

Methods

A case–control study was carried out during the period of January-July 2013 in northwest Ethiopia. Cases and controls were diagnosed using clinical presentation, the rk39 rapid diagnostic test and Direct Agglutination Test (DAT). A total of 283 (84.8% males versus 15.2% females) participants were interviewed. 90 cases and 193 controls were involved, matched by age, sex and geographical location with a ratio of 1:2 (case: controls). Univariate and backward multivariate conditional logistic regression were used to identify risk factors of VL.

Results

Elevated odds of VL was associated with goat ownership (OR = 6.4; 95%: confidence interval [Cl]: 1.5-28.4), living in houses with cracked wall (OR = 6.4; 95% Cl: 1.6-25.6), increased family size (OR = 1.3; 95% Cl: 1.0-1.8) and the number of days spent in the farm field (OR = 1.1; 95% Cl: 1.0-1.2). However, daily individual activities around the home and farm fields, mainly sleeping on a bed (OR = 0.2; 95%: Cl 0.03-0.9), sleeping outside the house under a bed net (OR = 0.1; 95% Cl: 0.02-0.36)] and smoking plant parts in the house during the night time (OR = 0.1; 95% Cl: 0.01-0.6) were associated with decreased odds of being VL case.

Conclusion

Our findings showed that use of bed net and smoke could be helpful for the prevention of VL in the area particularly among individuals who spend most of their time in the farm. VL control effort could be focused on improving housing conditions, such as sealing cracks and crevices inside and outside houses. Further research is warranted to elucidate the role of goats in the transmission of L. donovani, assess the impact of bed nets and the role of the traditional practice of smoking plants.

Attraction of Ethiopian phlebotomine sand flies (Diptera: Psychodidae) to light and sugar-yeast mixtures (CO(2))

BACKGROUND

Visceral leishmaniasis (VL) known as Kala-Azar is a serious systemic disease caused by Leishmania donovani parasites (Trypanosomatidae: Kinetoplastida). The disease is prevalent in the Indian Sub-continent, East Africa and Brazil. In Africa, the worst affected regions are in Sudan, with an estimated 15,000-20,000 cases annually and Ethiopia with 5,000-7,000 cases a year. The main vector of VL in Sudan and Northern Ethiopia is Phlebotomus orientalis, a sand fly frequently found in association with Acacia spp and Balanite spp woodlands.

METHODS

To optimize sampling of sand flies for epidemiological studies in remote areas we tested different means of attraction. Miniature suction traps employing 2AA batteries (3 V) were deployed in the up-draft orientation and baited with chemical light-sticks (Red, Yellow and Green), or bakers' yeast in sugar solution (emitting CO2 and perhaps other attractants). These traps were compared with standard CDC incandescent light traps employing 6 V batteries. Trials were conducted during two consecutive years at different localities around Sheraro, a town in West Tigray, Northern Ethiopia.

RESULTS

The sand fly species composition was similar but not identical in the different locations tested with different Sergentomyia spp. predominating. Phlebotomus spp. comprised less than 1% of the catches during the first year trials (November - December 2011) but increased markedly during the second year trials performed later in the dry season at the height of the sand fly season in February 2012. Although there did not appear to be a species bias towards different light wave-lengths, fermenting yeast in sugar solution attracted relatively more Phlebotomus spp. and Sergentomyia schwetzi.

CONCLUSIONS

Although the standard 6 V CDC incandescent light traps captured more sand flies, light-weight (~350 g) 3 V suction traps baited with chemical light-sticks were shown to be effective means of monitoring sand flies. Such traps operated without light and baited with yeast in sugar solution caught relatively more Phlebotomus spp.