Density of Aedes aegypti and Aedes albopictus and its association with number of residents and meteorological variables in the home environment of dengue endemic area, São Paulo, Brazil

Spatiotemporal Characterization of Dengue Incidence and Its Correlation to Climate Parameters in Indonesia

Dengue has become a public health concern in Indonesia since it was first found in 1968. This study aims to determine dengue hotspot areas and analyze the spatiotemporal distribution of dengue and its association with dominant climate parameters nationally. Monthly data for dengue and climate observations (i.e., rainfall, relative humidity, average, maximum, and minimum temperature) at the regency/city level were utilized. Dengue hotspot areas were determined through K-means clustering, while Singular Value Decomposition (SVD) determined dominant climate parameters and their spatiotemporal distribution. Results revealed four clusters: Cluster 1 comprised cities with medium to high Incidence Rates (IR) and high Case Densities (CD) in a narrow area. Cluster 2 has a high IR and low CD, and clusters 3 and 4 featured medium and low IR and CD, respectively. SVD analysis indicated that relative humidity and rainfall were the most influential parameters on IR across all clusters. Temporal fluctuations in the first mode of IR and climate parameters were clearly delineated. The spatial distribution of heterogeneous correlation between the first mode of rainfall and relative humidity to IR exhibited higher values, which were predominantly observed in Java, Bali, Nusa Tenggara, the eastern part of Sumatra, the southern part of Kalimantan, and several locations in Sulawesi.

The spread of Aedes albopictus (Diptera: Culicidae) in the islands of São Tomé and Príncipe

The mosquito Aedes albopictus (Diptera: Culicidae) is a vector species of the causal agents of Dengue, yellow fever, and Zika among other diseases pathogens. The species originated in Southeast Asia and has spread widely and rapidly in the last century. The species has been reported in localities from the Gulf of Guinea since the early 2000s, but systematic sampling has been scant. We sampled Ae. albopictus twice, in 2013 and 2023 across the altitudinal gradient in São Tomé and found that the species was present in all sampled years at altitudes up to 680 m. We also found some evidence of increases in proportional representation compared to Ae. aegypti over time. We report the presence of the species in Príncipe for the first time, suggesting that the range of Ae. albopictus is larger than previously thought. Finally, we use bioclimatic niche modeling to infer the potential range of Ae. albopictus and infer that the species has the potential to spread across a large portion of São Tomé and Príncipe. Our results suggest that Ae. albopictus has established itself as a resident species of the islands of the Gulf of Guinea and should be incorporated into the list of potential vectors that need to be surveyed and controlled.

Density of Aedes aegypti and dengue virus transmission risk in two municipalities of Northwestern Antioquia, Colombia

The high infestation of Aedes aegypti populations in Urabá, Antioquia, Colombia represents a risk factor for increased dengue morbidity and mortality. This study aimed to determine the risk of dengue transmission by estimating the population of Ae. aegypti using entomological indices, density of females per dwelling and inhabitant, and virological surveillance in two municipalities in Colombia. A cross-sectional study was conducted with quarterly entomological surveys in three neighborhoods of Apartadó and Turbo between 2021 and 2022. Aedes indices and vector density per dwelling and per inhabitant were calculated. The Kernel method was used for spatial analysis, and correlations between climatic variables and mosquito density were examined. Virus detection and serotyping in mosquitoes was performed using single-step reverse transcription polymerase chain reaction. The housing, reservoir, and Breteau indices were 48.9%, 29.5%, and 70.2%, respectively. The mean density of Ae. aegypti was 1.47 females / dwelling and 0.51 females / inhabitant. The overall visual analysis showed several critical points in the neighborhoods studied. There was significant correlation of vector density and relative humidity and precipitation in the neighborhoods 29 de noviembre and 24 de diciembre. Additionally, serotypes DENV-1 and DENV-2 were found. The overall indices for dwellings, reservoirs, and Breteau were lower than those recorded in 2014 in Urabá. The vector density results in this study were similar to those reported in other studies conducted in Latin America, and vector infection was detected. The Aedes and density indices are complementary, emphasizing the importance of continuous surveillance of Ae. aegypti to inform appropriate control strategies and prevent future dengue outbreaks in these municipalities.

Aedes aegypti abundance in urban neighborhoods of Maricopa County, Arizona, is linked to increasing socioeconomic status and tree cover

BACKGROUND

Understanding coupled human-environment factors which promote Aedes aegypti abundance is critical to preventing the spread of Zika, chikungunya, yellow fever and dengue viruses. High temperatures and aridity theoretically make arid lands inhospitable for Ae. aegypti mosquitoes, yet their populations are well established in many desert cities.

METHODS

We investigated associations between socioeconomic and built environment factors and Ae. aegypti abundance in Maricopa County, Arizona, home to Phoenix metropolitan area. Maricopa County Environmental Services conducts weekly mosquito surveillance with CO2-baited Encephalitis Vector Survey or BG-Sentinel traps at > 850 locations throughout the county. Counts of adult female Ae. aegypti from 2014 to 2017 were joined with US Census data, precipitation and temperature data, and 2015 land cover from high-resolution (1 m) aerial images from the National Agricultural Imagery Program.

RESULTS

From 139,729 trap-nights, 107,116 Ae. aegypti females were captured. Counts were significantly positively associated with higher socioeconomic status. This association was partially explained by higher densities of non-native landscaping in wealthier neighborhoods; a 1% increase in the density of tree cover around the trap was associated with a ~ 7% higher count of Ae. aegypti (95% CI: 6-9%).

CONCLUSIONS

Many models predict that climate change will drive aridification in some heavily populated regions, including those where Ae. aegypti are widespread. City climate change adaptation plans often include green spaces and vegetation cover to increase resilience to extreme heat, but these may unintentionally create hospitable microclimates for Ae. aegypti. This possible outcome should be addressed to reduce the potential for outbreaks of Aedes-borne diseases in desert cities.

Impact of tetravalent dengue vaccination with screening, ADE, and altered infectivity on single-serotype dengue and Zika transmission

Acquired immunity to a dengue virus serotype (whether by infection or the only licensed dengue vaccine) can produce antibody-dependent enhancement (ADE) in later infections with another dengue serotype, resulting in higher viral loads and more severe symptoms such as dengue hemorrhagic fever, unless the person already has immunity to multiple dengue serotypes. Screening to confirm dengue seropositivity is therefore recommended before vaccination. Recent studies suggest that the closely-related Zika virus may also interact with dengue through ADE. This study uses a mathematical model to evaluate the likely impact of imperfect screening and dengue vaccination on the spread of both viruses in a population where only one dengue serotype circulates, although the vaccine may take against any or all of the four recognized serotypes. Analysis focuses on the reproductive numbers of the viruses. Results indicate that vaccination increases the spread of Zika through induced ADE, while its impact on the spread of dengue depends on screening specificity and serotype-specific vaccine efficacies, as well as the intensity of ADE. Numerical analysis identifies the roles played by age-in and catch-up vaccination as well as screening characteristics and prior dengue exposure.

Effects of high temperatures and heatwaves on dengue fever: a systematic review and meta-analysis

BACKGROUND

Studies have shown that dengue virus transmission increases in association with ambient temperature. We performed a systematic review and meta-analysis to assess the effect of both high temperatures and heatwave events on dengue transmission in different climate zones globally.

METHODS

A systematic literature search was conducted in PubMed, Scopus, Embase, and Web of Science from January 1990 to September 20, 2022. We included peer reviewed original observational studies using ecological time series, case crossover, or case series study designs reporting the association of high temperatures and heatwave with dengue and comparing risks over different exposures or time periods. Studies classified as case reports, clinical trials, non-human studies, conference abstracts, editorials, reviews, books, posters, commentaries; and studies that examined only seasonal effects were excluded. Effect estimates were extracted from published literature. A random effects meta-analysis was performed to pool the relative risks (RRs) of dengue infection per 1 °C increase in temperature, and further subgroup analyses were also conducted. The quality and strength of evidence were evaluated following the Navigation Guide systematic review methodology framework. The review protocol has been registered in the International Prospective Register of Systematic Reviews (PROSPERO).

FINDINGS

The study selection process yielded 6367 studies. A total of 106 studies covering more than four million dengue cases fulfilled the inclusion criteria; of these, 54 studies were eligible for meta-analysis. The overall pooled estimate showed a 13% increase in risk of dengue infection (RR = 1.13; 95% confidence interval (CI): 1.11-1.16, I² = 98.0%) for each 1 °C increase in high temperatures. Subgroup analyses by climate zones suggested greater effects of temperature in tropical monsoon climate zone (RR = 1.29, 95% CI: 1.11-1.51) and humid subtropical climate zone (RR = 1.20, 95% CI: 1.15-1.25). Heatwave events showed association with an increased risk of dengue infection (RR = 1.08; 95% CI: 0.95-1.23, I² = 88.9%), despite a wide confidence interval. The overall strength of evidence was found to be "sufficient" for high temperatures but "limited" for heatwaves. Our results showed that high temperatures increased the risk of dengue infection, albeit with varying risks across climate zones and different levels of national income.

INTERPRETATION

High temperatures increased the relative risk of dengue infection. Future studies on the association between temperature and dengue infection should consider local and regional climate, socio-demographic and environmental characteristics to explore vulnerability at local and regional levels for tailored prevention.

FUNDING

Australian Research Council Discovery Program.

Surveillance of Aedes aegypti and Aedes albopictus (Diptera: Culicidae) as a Method for Prevention of Arbovirus Transmission in Urban and Seaport Areas of the Southern Coast of Brazil

Entomological surveillance is a traditional method to measure presence, distribution, and seasonal variation of vectors in urban areas, and is essential to targeted control activities to prevent arbovirus transmission. Ovitraps as one of the main components of surveillance programs, enable determination of female oviposition behavior, as well as identification of seasonal variations of the vector. The goals of this study were 1) to detect the mosquitos (Aedes aegypti Linnaeus) and (Aedes albopictus Skuse) (Diptera:Culicidae), in Paranaguá city, 2) to assess ovitrap positive index (OPI), egg density index (EDI), and their relationship with meteorological variables, and 3) to evaluate the vertical transmission of dengue, Zika, and chikungunya in Ae. aegypti and Ae. albopictus. The study was carried out in urban areas of Paranaguá city, an important port region of Brazil, from June 2017 to November 2018. The city was divided into 16 area-clusters. Three-hundred and thirty-one ovitraps were installed monthly, remaining for four days in selected places. Kernel density maps were done to compare the spatiotemporal distribution of collected eggs. Areas which maintained constant oviposition associated with vector activity were identified and were found to overlap the area-clusters with the highest EDI. As viral RNA was not detected, vertical transmission was likely not a maintenance mechanism of arbovirus circulation in Ae. aegypti and Ae. albopictus vectors. This study reiterates the importance, efficiency, and feasibility of ovitraps to monitor the presence and dynamics of Aedes spp. populations.

Using machine learning to understand microgeographic determinants of the Zika vector, Aedes aegypti

There are limited data on why the 2016 Zika outbreak in Miami-Dade County, Florida was confined to certain neighborhoods. In this research, Aedes aegypti, the primary vector of Zika virus, are studied to examine neighborhood-level differences in their population dynamics and underlying processes. Weekly mosquito data were acquired from the Miami-Dade County Mosquito Control Division from 2016 to 2020 from 172 traps deployed around Miami-Dade County. Using random forest, a machine learning method, predictive models of spatiotemporal dynamics of Ae. aegypti in response to meteorological conditions and neighborhood-specific socio-demographic and physical characteristics, such as land-use and land-cover type and income level, were created. The study area was divided into two groups: areas affected by local transmission of Zika during the 2016 outbreak and unaffected areas. Ae. aegypti populations in areas affected by Zika were more strongly influenced by 14- and 21-day lagged weather conditions. In the unaffected areas, mosquito populations were more strongly influenced by land-use and day-of-collection weather conditions. There are neighborhood-scale differences in Ae. aegypti population dynamics. These differences in turn influence vector-borne disease diffusion in a region. These results have implications for vector control experts to lead neighborhood-specific vector control strategies and for epidemiologists to guide vector-borne disease risk preparations, especially for containing the spread of vector-borne disease in response to ongoing climate change.

The MosHouse® Trap: Evaluation of the Efficiency in Trapping Sterile Aedes aegypti Males in Semi-Field Conditions

Arbovirus diseases, such as dengue, chikungunya, and Zika, are important public health problems. Controlling the major vector, Aedes aegypti, is the only approach to suppressing these diseases. The surveillance of this mosquito species needs effective collecting methods. In this study, a simple MosHouse sticky trap was evaluated in a semi-field condition. Our results demonstrated the efficiency of this trap in collecting Ae. aegypti males, and no significant difference (p > 0.05) in the numbers of males was detected when compared with the widely used BG- Sentinel trap. However, there were significantly lower numbers of females (p < 0.05) collected using the MosHouse trap when compared to the BG-Sentinel trap. We also found a significant difference (p < 0.05) in the collected numbers between irradiated and non-irradiated males. More irradiated males were collected in the MosHouse traps. The improvement of male collection was achieved with the addition of a sugar stick and sticky flags. Significantly higher numbers of males were collected in the MosHouse trap with sticky flags compared to the original one when they were released independently of females, but both were collected in higher numbers when they were released together (p < 0.05). In conclusion, our experiments demonstrated that the MosHouse trap could sample Ae. aegypti, especially males, as efficiently as the established BG-Sentinel trap, while the cost was more than 50 times lower, showing the potential of the MosHouse trap for improved Ae. aegypti male and female surveillance with very large numbers of traps at affordable costs. In addition, significantly (p < 0.001) increased male sampling was achieved by adding an external sticky flag on the MosHouse trap, providing an avenue for further development of the novel male-trapping strategy.

Effect of the Rural and Urban Microclimate on Mosquito Richness and Abundance in Yucatan State, Mexico

The objective of this study was to analyze the effect of the rural and urban microclimate on the presence of mosquitoes. Temperature (T) and relative humidity (RH; indoors and outdoors), as well as mosquito richness and abundance were measured in two sites (urban and rural) of the Yucatan State, Mexico. Species richness was higher in the urban site, whereas mosquito abundance was higher in the rural site. The microclimates of urban and rural housing differently affect mosquito richness and abundance. Mosquito richness and abundance were higher outdoors than indoors in the urban site, but they were higher indoors than outdoors in the rural site. For the urban site, analysis of the relation of T and RH with the registered parameters revealed that species richness increased with increasing indoor RH, and that mosquito abundance increased with increasing indoor T and RH. In the rural site, species richness was not affected, but abundance increased with increasing T and RH (indoors as well as outdoors). Results are discussed in the context of the management of mosquito transmitted diseases. No IRB approval was necessary since no ethical implications were identified to be reviewed by the ethical committee for the research of the ECOSUR Institution.

Bionomic aspects of dengue vectors Aedes aegypti and Aedes albopictus at domestic settings in urban, suburban and rural areas in Gampaha District, Western Province of Sri Lanka

Background

The lack of information on behavioural patterns of Aedes aegypti and Aedes albopictus has become a significant limitation in vector control and disease management programmes. Therefore, the current study was focused on determining some bionomics aspects: breeding, resting, host-seeking and feeding preferences of Ae. aegypti and Ae. albopictus in Sri Lanka.

Methods

Larval and adult surveys were conducted from April 2017 to April 2019 monthly in six selected Medical Officer of Health (MOH) areas in Gampaha Distinct, Western province, Sri Lanka, representing urban, suburban and rural settings. Resting preferences of adult mosquitoes were observed from indoor and outdoor places using a Prockopack aspirator. The information on resting height, surface, material and locality was recorded. Human-baited double-net traps were used to determine the host-seeking time of Aedes mosquitoes. Statistical differences in the spatial distribution of mosquitoes in selected MOH areas and prevalence of vectors were analysed using general linear model (GLM). A chi-square test was used to analyse the resting behaviour.

Results

Total of 19,835 potential breeding sites were examined at 13,563 premises, and 18.5% (n = 1856) were positive for Aedes larvae. Distribution of Ae. aegypti and Ae. albopictus was statistically significant at species level (df = 1; F = 137.134; P < 0.05 GLM) and study setting (df = 2; F = 8.125; P < 0.05). Aedes aegypti breeding was found mainly in temporary removals (18.8%; n = 34), discarded non-degradables (12.15%; n = 22) and tyres (9.95%; n = 18). Natural (14.7%; n = 246) and temporary removals (13.6%; n = 227) and discarded non-reusable items were the key ovipositing sites for Ae. albopictus. In the adult mosquito survey, the majority was comprised of Ae. albopictus (54.5%; n = 999), which denoted exophilic nature (90.8%; n = 758), and 45.5% (n = 835) represented by Ae. aegypti mosquitoes who were mainly endophilic (84.3%; n = 842). Aedes aegypti rested on cloth hangings and curtains, followed by the furniture, while Aedes albopictus was predominant in outdoor vegetation. In both vectors, biting patterns denoted a typical diurnal pattern with two peaks of host-seeking and biting activity in the morning and afternoon.

Conclusions

The majority (80%) of the larval habitats were artificial containers. The use of larvicides for vector control as the prominent measure is questionable since applying these chemicals may target only 20% of the total breeding grounds, which are permanent. The resting places of adult mosquitoes are mainly indoors. Therefore, using thermal space spraying of insecticide may not be appropriate, and indoor residual spraying is recommended as a suitable intervention to target adult mosquitoes. This study warrants a holistic vector control approach for all medically important mosquitoes and insects, ensuring the rational use of finance and resources.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05261-3.

Culex quinquefasciatus predominance during integrated mosquito surveillance in an urban area of the Brazilian Amazon

Abstract The presence and establishment of Culicidae in urban areas increase the transmissibility of tropical diseases, since some species can participate as vectors of pathogens. Thus, this study aimed to evaluate the indoor and outdoor abundance of immature and adult populations of Culicidae at the urban area of Porto Velho, Rondônia. Mosquitoes were captured using electric aspirators and ovitraps in September and December 2018 in 27 households spread over nine neighborhoods. A total of 2,342 specimens were collected, distributed among five species, of which Culex quinquefasciatus (Say, 1823), Aedes aegypti (Linnaeus, 1762) and Aedes albopictus (Skuse, 1894) were the most abundant. Considering the sum total obtained by both techniques, more mosquitoes were captured indoors than outdoors. However, the GLM estimates for the ovitrap technique showed that immature Ae. aegypti, Ae. albopictus and Cx. quinquefasciatus were significantly more abundant in the outdoors, on average. The opposite result was observed for electrical aspiration, in which Ae. aegypti and Cx. quinquefasciatus adults were more abundant indoors. The average number of winged Ae. albopictus showed no significant difference between indoors and outdoors. Our findings corroborate the data on the abundance and incidence of these three species in other regions of Brazil, highlighting the need for continuous surveillance due to their importance in disease transmission to humans. We also demonstrated that the ovitrap is a sensitive device to monitor Cx. quinquefasciatus larvae and wild species that occasionally frequent urban areas, and thus can be used for surveillance, especially when there are budgetary constraints. Therefore, we emphasize that the combination of techniques, in addition to identifying which species and which stage of development are more frequent inside and outside households, also allows for the implementation of specific and integrated control measures.

Mapping the spatial distribution of the dengue vector Aedes aegypti and predicting its abundance in northeastern Thailand using machine-learning approach

BACKGROUND

Mapping the spatial distribution of the dengue vector Aedes (Ae.) aegypti and accurately predicting its abundance are crucial for designing effective vector control strategies and early warning tools for dengue epidemic prevention. Socio-ecological and landscape factors influence Ae. aegypti abundance. Therefore, we aimed to map the spatial distribution of female adult Ae. aegypti and predict its abundance in northeastern Thailand based on socioeconomic, climate change, and dengue knowledge, attitude and practices (KAP) and/or landscape factors using machine learning (ML)-based system.

METHOD

A total of 1066 females adult Ae. aegypti were collected from four villages in northeastern Thailand during January-December 2019. Information on household socioeconomics, KAP regarding climate change and dengue, and satellite-based landscape data were also acquired. Geographic information systems (GIS) were used to map the household-based spatial distribution of female adult Ae. aegypti abundance (high/low). Five popular supervised learning models, logistic regression (LR), support vector machine (SVM), k-nearest neighbor (kNN), artificial neural network (ANN), and random forest (RF), were used to predict females adult Ae. aegypti abundance (high/low). The predictive accuracy of each modeling technique was calculated and evaluated. Important variables for predicting female adult Ae. aegypti abundance were also identified using the best-fitted model.

RESULTS

Urban areas had higher abundance of female adult Ae. aegypti compared to rural areas. Overall, study respondents in both urban and rural areas had inadequate KAP regarding climate change and dengue. The average landscape factors per household in urban areas were rice crop (47.4%), natural tree cover (17.8%), built-up area (13.2%), permanent wetlands (21.2%), and rubber plantation (0%), and the corresponding figures for rural areas were 12.1, 2.0, 38.7, 40.1 and 0.1% respectively. Among all assessed models, RF showed the best prediction performance (socioeconomics: area under curve, AUC = 0.93, classification accuracy, CA = 0.86, F1 score = 0.85; KAP: AUC = 0.95, CA = 0.92, F1 = 0.90; landscape: AUC = 0.96, CA = 0.89, F1 = 0.87) for female adult Ae. aegypti abundance. The combined influences of all factors further improved the predictive accuracy in RF model (socioeconomics + KAP + landscape: AUC = 0.99, CA = 0.96 and F1 = 0.95). Dengue prevention practices were shown to be the most important predictor in the RF model for female adult Ae. aegypti abundance in northeastern Thailand.

CONCLUSION

The RF model is more suitable for the prediction of Ae. aegypti abundance in northeastern Thailand. Our study exemplifies that the application of GIS and machine learning systems has significant potential for understanding the spatial distribution of dengue vectors and predicting its abundance. The study findings might help optimize vector control strategies, future mosquito suppression, prediction and control strategies of epidemic arboviral diseases (dengue, chikungunya, and Zika). Such strategies can be incorporated into One Health approaches applying transdisciplinary approaches considering human-vector and agro-environmental interrelationships.

Dengue disease dynamics are modulated by the combined influences of precipitation and landscape: A machine learning approach

BACKGROUND

Dengue is an endemic vector-borne disease influenced by environmental factors such as landscape and climate. Previous studies separately assessed the effects of landscape and climate factors on mosquito occurrence and dengue incidence. However, both factors concurrently coexist in time and space and can interact, affecting mosquito development and dengue disease transmission. For example, eggs laid in a suitable environment can hatch after being submerged in rain water. It has been difficult for conventional statistical modeling approaches to demonstrate these combined influences due to mathematical constraints.

OBJECTIVES

To investigate the combined influences of landscape and climate factors on mosquito occurrence and dengue incidence.

METHODS

Entomological, epidemiological, and landscape data from the rainy season (July-December) were obtained from respective government agencies in Metropolitan Manila, Philippines, from 2012 to 2014. Temperature, precipitation and vegetation data were obtained through remote sensing. A random forest algorithm was used to select the landscape and climate variables. Afterward, using the identified key variables, a model-based (MOB) recursive partitioning was implemented to test the combined influences of landscape and climate factors on ovitrap index (vector mosquito occurrence) and dengue incidence.

RESULTS

The MOB recursive partitioning for ovitrap index indicated a high sensitivity of vector mosquito occurrence on environmental conditions generated by a combination of high residential density areas with low precipitation. Moreover, the MOB recursive partitioning indicated high sensitivity of dengue incidence to the effects of precipitation in areas with high proportions of residential density and commercial areas.

CONCLUSIONS

Dengue dynamics are not solely influenced by individual effects of either climate or landscape, but rather by their synergistic or combined effects. The presented findings have the potential to target vector surveillance in areas identified as suitable for mosquito occurrence under specific climatic conditions and may be relevant as part of urban planning strategies to control dengue.

Entomovirological Surveillance in Schools: Are They a Source for Arboviral Diseases Transmission?

Surveillance and control activities for virus-transmitting mosquitoes have primarily focused on dwellings. There is little information about viral circulation in heavily trafficked places such as schools. We collected and analyzed data to assess the presence and prevalence of dengue, chikungunya, and Zika viruses in mosquitoes, and measured Aedes indices in schools in Medellín (Colombia) between 2016-2018. In 43.27% of 2632 visits we collected Aedes adults, creating 883 pools analyzed by RT-PCR. 14.27% of pools yielded positive for dengue or Zika (infection rates of 1.75-296.29 for Aedes aegypti). Ae. aegypti was more abundant and had a higher infection rate for all studied diseases. Aedes indices varied over time. There was no association between Aedes abundance and mosquito infection rates, but the latter did correlate with cases of arboviral disease and climate. Results suggest schools are important sources of arbovirus and health agencies should include these sites in surveillance programs; it is essential to know the source for arboviral diseases transmission and the identification of the most population groups exposed to these diseases to research and developing new strategies.

Population mobility, demographic, and environmental characteristics of dengue fever epidemics in a major city in Southeastern Brazil, 2007-2015

Around 14% of world dengue virus (DENV) cases occur in the Americas, most of them in Brazil. While socioeconomic, environmental, and behavioral correlates have been analyzed thoroughly, the role played by population mobility on DENV epidemics, especially at the local level, remains scarce. This study assesses whether the daily pattern of population mobility is associated with DENV incidence in Campinas, a Brazilian major city with over 1.2 million inhabitants in São Paulo State. DENV notifications from 2007 to 2015 were geocoded at street level (n = 114,884) and combined with sociodemographic and environmental data from the 2010 population census. Population mobility was extracted from the Origin-Destination Survey (ODS), carried out in 2011, and daily precipitation was obtained from satellite imagery. Multivariate zero-inflated negative binomial regression models were applied. High population mobility presented a relevant positive effect on higher risk for DENV incidence. High income and residence in apartments were found to be protective characteristics against the disease, while unpaved streets, number of strategic points (such as scrapyards and tire repair shops), and precipitation were consistently risk factors.

Modelling distributions of Aedes aegypti and Aedes albopictus using climate, host density and interspecies competition

Florida faces the challenge of repeated introduction and autochthonous transmission of arboviruses transmitted by Aedes aegypti and Aedes albopictus. Empirically-based predictive models of the spatial distribution of these species would aid surveillance and vector control efforts. To predict the occurrence and abundance of these species, we fit a mixed-effects zero-inflated negative binomial regression to a mosquito surveillance dataset with records from more than 200,000 trap days, representative of 53% of the land area and ranging from 2004 to 2018 in Florida. We found an asymmetrical competitive interaction between adult populations of Aedes aegypti and Aedes albopictus for the sampled sites. Wind speed was negatively associated with the occurrence and abundance of both vectors. Our model predictions show high accuracy (72.9% to 94.5%) in validation tests leaving out a random 10% subset of sites and data since 2017, suggesting a potential for predicting the distribution of the two Aedes vectors.

Implications of the COVID-19 Lockdown on Dengue Transmission in Malaysia

We aim to investigate the effect of large-scale human movement restrictions during the COVID-19 lockdown on both the dengue transmission and vector occurrences. This study compared the weekly dengue incidences during the period of lockdown to the previous years (2015 to 2019) and a Seasonal Autoregressive Integrated Moving Average (SARIMA) model that expected no movement restrictions. We found that the trend of dengue incidence during the first two weeks (stage 1) of lockdown decreased significantly with the incidences lower than the lower confidence level (LCL) of SARIMA. By comparing the magnitude of the gradient of decrease, the trend is 319% steeper than the trend observed in previous years and 650% steeper than the simulated model, indicating that the control of population movement did reduce dengue transmission. However, starting from stage 2 of lockdown, the dengue incidences demonstrated an elevation and earlier rebound by four weeks and grew with an exponential pattern. We revealed that Aedes albopictus is the predominant species and demonstrated a strong correlation with the locally reported dengue incidences, and therefore we proposed the possible diffusive effect of the vector that led to a higher acceleration of incidence rate.

A serological framework to investigate acute primary and post-primary dengue cases reporting across the Philippines

BACKGROUND

In dengue-endemic countries, targeting limited control interventions to populations at risk of severe disease could enable increased efficiency. Individuals who have had their first (primary) dengue infection are at risk of developing more severe secondary disease, thus could be targeted for disease prevention. Currently, there is no reliable algorithm for determining primary and post-primary (infection with more than one flavivirus) status from a single serum sample. In this study, we developed and validated an immune status algorithm using single acute serum samples from reporting patients and investigated dengue immuno-epidemiological patterns across the Philippines.

METHODS

During 2015/2016, a cross-sectional sample of 10,137 dengue case reports provided serum for molecular (anti-DENV PCR) and serological (anti-DENV IgM/G capture ELISA) assay. Using mixture modelling, we re-assessed IgM/G seroprevalence and estimated functional, disease day-specific, IgG:IgM ratios that categorised the reporting population as negative, historical, primary and post-primary for dengue. We validated our algorithm against WHO gold standard criteria and investigated cross-reactivity with Zika by assaying a random subset for anti-ZIKV IgM and IgG. Lastly, using our algorithm, we explored immuno-epidemiological patterns of dengue across the Philippines.

RESULTS

Our modelled IgM and IgG seroprevalence thresholds were lower than kit-provided thresholds. Individuals anti-DENV PCR+ or IgM+ were classified as active dengue infections (83.1%, 6998/8425). IgG- and IgG+ active dengue infections on disease days 1 and 2 were categorised as primary and post-primary, respectively, while those on disease days 3 to 5 with IgG:IgM ratios below and above 0.45 were classified as primary and post-primary, respectively. A significant proportion of post-primary dengue infections had elevated anti-ZIKV IgG inferring previous Zika exposure. Our algorithm achieved 90.5% serological agreement with WHO standard practice. Post-primary dengue infections were more likely to be older and present with severe symptoms. Finally, we identified a spatio-temporal cluster of primary dengue case reporting in northern Luzon during 2016.

CONCLUSIONS

Our dengue immune status algorithm can equip surveillance operations with the means to target dengue control efforts. The algorithm accurately identified primary dengue infections who are at risk of future severe disease.

Gravitrap deployment for adult Aedes aegypti surveillance and its impact on dengue cases

House Index, Container Index, and Breteau Index are the most commonly used indices for dengue vector surveillance. However, these larval indices are a poor proxy for measuring the adult population—which is responsible for disease transmission. Information on the adult distribution and density are important for assessing transmission risk as well as for developing effective control strategies. This study introduces a new entomological index, Gravitrap aegypti index (GAI), which estimates the adult female Aedes aegypti population in the community and presents its association with dengue cases. Gravitraps were deployed across 34 treatment sites in Singapore from September 2013 to September 2016. The GAI, derived from the Gravitrap surveillance data, was analysed to investigate the spatio-temporal patterns of the Ae. aegypti population in Singapore. The index was further categorised into low, moderate, and high-risk groups and its association with dengue cases were examined. A Before-After Control Impact analysis was performed to evaluate the epidemiology impact of Gravitrap system on dengue transmission. The Ae. aegypti population exhibits a seasonal pattern, and spatial heterogeneity in Ae. aegypti abundance was observed among treatment sites. The Ae. aegypti population was also found to be unevenly distributed among floors of an apartment block, with low floors (floors 1–4) having a higher abundance of mosquitoes trapped than mid (floors 5–8) and high (floors ≥9) floors. Areas with high GAI were shown to have higher dengue case count. Gravitrap has also demonstrated to be a good dengue control tool. The contribution of cases by treatment sites to the national numbers was lower after Gravitraps deployment. The GAI, which is of better relevance to dengue transmission risk, could be recommended as an indicator for decision making in vector control efforts, and to monitor the spatio-temporal variability of the adult Aedes population in the country. In addition, findings from this study indicate that Gravitraps can be used as a dengue control tool to reduce dengue transmission.

In the absence of an effective vaccine: vector surveillance and control remain the key strategy for dengue prevention and control. The collection of the adult female Aedes mosquito is thus important to understand disease transmission dynamics. Information on its distribution and density are also essential for assessing transmission risk as well as for devising an effective control strategy. Here, we described a new approach to dengue vector surveillance based on adult female Aedes trapping using Gravitraps. Using the Gravitrap surveillance data, we derived a new entomological index, Gravitrap aegypti index (GAI), which estimates the adult female Ae. aegypti population in the community and presents its association with dengue cases. When analysed, the index can provide useful information on the spatio-temporal distribution of the Ae. aegypti population in the country and hence, assist planning of vector control. The GAI, which is of better relevance to dengue transmission risk, could be used as an indicator for decision making in vector control efforts, and to monitor the spatio-temporal variability of the adult Aedes population. In addition, findings from this study indicate that Gravitraps can be used as a dengue control tool to reduce dengue transmission.

Land Use Changes and Cluster Identification of Dengue Hemorrhagic Fever Cases in Bandung, Indonesia

Dengue Hemorrhagic Fever (DHF) in Indonesia has increased steadily with Bandung as a hyper-endemic area holding a high number of cases for years. This study aimed to identify cluster areas and their correlation with land use changes which was indicated by changes of Normalized Difference Vegetation Index (NDVI). Hospital surveillance of 28,327 cases during 2008–2013 was geo-coded into sub-district levels and analyzed to find cluster areas over time and space using SaTScan and ArcGIS. Spearman correlation was used to analyze NDVI with Incidence Rate (IR) in each area. IR of DHF cases tended to increase over 6 years during high precipitation period. Cases were concentrated in several cluster areas in 2009 then moved to eastern part of the city in 2013. NDVI had negative correlation with IR in 2008 (r = −0.258; p = 0.001) and positive correlation in 2012 (r = 0.193; p = 0.017). Clear geographical pattern by cluster identification overtime is beneficial for targeting appropriate vector-control program.

A Mapping Review on Urban Landscape Factors of Dengue Retrieved from Earth Observation Data, GIS Techniques, and Survey Questionnaires

To date, there is no effective treatment to cure dengue fever, a mosquito-borne disease which has a major impact on human populations in tropical and sub-tropical regions. Although the characteristics of dengue infection are well known, factors associated with landscape are highly scale dependent in time and space, and therefore difficult to monitor. We propose here a mapping review based on 78 articles that study the relationships between landscape factors and urban dengue cases considering household, neighborhood and administrative levels. Landscape factors were retrieved from survey questionnaires, Geographic Information Systems (GIS), and remote sensing (RS) techniques. We structured these into groups composed of land cover, land use, and housing type and characteristics, as well as subgroups referring to construction material, urban typology, and infrastructure level. We mapped the co-occurrence networks associated with these factors, and analyzed their relevance according to a three-valued interpretation (positive, negative, non significant). From a methodological perspective, coupling RS and GIS techniques with field surveys including entomological observations should be systematically considered, as none digital land use or land cover variables appears to be an univocal determinant of dengue occurrences. Remote sensing urban mapping is however of interest to provide a geographical frame to distribute human population and movement in relation to their activities in the city, and as spatialized input variables for epidemiological and entomological models.

What Is the Value of Different Zika Vaccination Strategies to Prevent and Mitigate Zika Outbreaks?

BACKGROUND

While the 2015-2016 Zika epidemics prompted accelerated vaccine development, decision makers need to know the potential economic value of vaccination strategies.

METHODS

We developed models of Honduras, Brazil, and Puerto Rico, simulated targeting different populations for Zika vaccination (women of childbearing age, school-aged children, young adults, and everyone) and then introduced various Zika outbreaks. Sensitivity analyses varied vaccine characteristics.

RESULTS

With a 2% attack rate ($5 vaccination), compared to no vaccination, vaccinating women of childbearing age cost $314-$1664 per case averted ($790-$4221/disability-adjusted life-year [DALY] averted) in Honduras, and saved $847-$1644/case averted in Brazil, and $3648-$4177/case averted in Puerto Rico, varying with vaccination coverage and efficacy (societal perspective). Vaccinating school-aged children cost $718-$1849/case averted (≤$5002/DALY averted) in Honduras, saved $819-$1609/case averted in Brazil, and saved $3823-$4360/case averted in Puerto Rico. Vaccinating young adults cost $310-$1666/case averted ($731-$4017/DALY averted) in Honduras, saved $953-$1703/case averted in Brazil, and saved $3857-$4372/case averted in Puerto Rico. Vaccinating everyone averted more cases but cost more, decreasing cost savings per case averted. Vaccination resulted in more cost savings and better outcomes at higher attack rates.

CONCLUSIONS

When considering transmission, while vaccinating everyone naturally averted the most cases, specifically targeting women of childbearing age or young adults was the most cost-effective.

Estimating absolute indoor density of Aedes aegypti using removal sampling

BACKGROUND

Quantification of adult Aedes aegypti abundance indoors has relied on estimates of relative density (e.g. number of adults per unit of sampling or time), most commonly using traps or timed collections using aspirators. The lack of estimates of the sensitivity of collections and lack of a numerical association between relative and the absolute density of adult Ae. aegypti represent a significant gap in vector surveillance. Here, we describe the use of sequential removal sampling to estimate absolute numbers of indoor resting Ae. aegypti and to calculate calibration coefficients for timed Prokopack aspirator collections in the city of Merida, Yucatan State, Mexico. The study was performed in 200 houses that were selected based on recent occurrence of Aedes-borne viral illness in residents. Removal sampling occurred in 10-minute sampling rounds performed sequentially until no Ae. aegypti adult was collected for 3 hours or over 2 consecutive 10-minute periods.

RESULTS

A total of 3439 Ae. aegypti were collected. The sensitivity of detection of positive houses in the first sampling round was 82.5% for any adult Ae. aegypti, 78.5% for females, 75.5% for males and 73.3% for blood-fed females. The total number of Ae. aegypti per house was on average ~5 times higher than numbers collected for the first sampling round. There was a positive linear relationship between the relative density of Ae. aegypti collected during the first 10-min round and the absolute density for all adult metrics. Coefficients from the linear regression were used to calibrate numbers from 10-min collections into estimates of absolute indoor Ae. aegypti density for all adults, females and males.

CONCLUSIONS

Exhaustive removal sampling represents a promising method for quantification of absolute indoor Ae. aegypti density, leading to improved entomological estimates of mosquito distribution, a key measure in the assessments of the risk pathogen transmission, disease modeling and the evaluation of vector control interventions.

Abiotic factors and population dynamic of Aedes aegypti and Aedes albopictus in an endemic area of dengue in Brazil

Aedes aegypti and Aedes albopictus are exotic species in the Americas with high epidemiological relevance as they are vectors of many pathogens. This study aimed at understanding the population dynamics of A. aegypti and A. albopictus and the influence of abiotic factors in an endemic area of dengue. The study was conducted in the urban area of Campo Grande, Mato Grosso do Sul, Brazil, over one year. In seven regions of the city, 50 ovitraps were installed in each neighborhood. The development of the larvae was monitored under controlled laboratory conditions until they reached the adult phase. A total of 50,900 eggs of Aedes sp. were collected, 26,073 of which reached adulthood: 25,496 (97.8 %) A. aegypti and 540 (2.1%) A. albopictus. A. aegypti was observed in all months during the study. The highest number of A. albopictus eggs were collected in June, while in August and September, an absence of this species was noted. Abiotic factors such as temperature, humidity and rainfall were responsible for the observed fluctuations in the mosquito population. The presence of A. albopictus in the urban area of the city is concerning because it could become a potential vector for other arboviruses that afflict human populations. The occurrence of these species in Campo Grande reinforces the need for constant entomological and epidemiological surveillance so that informed actions could be taken to decrease potential breeding sites.

Wing Geometry Analysis of Aedes aegypti (Diptera, Culicidae), a Dengue Virus Vector, from Multiple Geographical Locations of Samut Songkhram, Thailand

BACKGROUND

Dengue Haemorrhagic Fever (DHF) is a mosquito-borne disease and remains a major public health problem, especially in tropical and temperate countries. Studying wing morphometric of Aedes aegypti as a mosquito vector of DHF can help to better understand biological process of the mosquito adaptation to the environment. We aimed to study the geometric morphometric of Ae. aegypti from multiple geographical areas.

METHODS

Samples were collected from Samut Songkhram Province in Thailand, including coastal, residential and cultivated areas, by Ovitrap once per month during Oct to Nov 2016.

RESULTS

According to size variation analysis of Ae. aegypti, the female mosquito in a cultivated area was significantly different from those in the coastal and residential areas (P< 0.05). Whereas male Ae. aegypti in a cultivated area were significantly different from those in a residential area (P< 0.05). The shape variation of both female and male Ae. aegypti from all areas was statistically different (P< 0.05).

CONCLUSION

Normally, living organisms, including mosquitoes, are adapted to their environment. The studied geographical locations affect Ae. aegypti morphology.

Wing morphometric variability in Aedes aegypti (Diptera: Culicidae) from different urban built environments

BACKGROUND

Aedes aegypti is the main vector of the dengue, Zika and several other arboviruses. It is highly adapted to urbanized environments and can be found worldwide. Mosquito population control is considered the best strategy for fighting mosquito-borne diseases, making an understanding of their population dynamics vital for the development of more effective vector control programs. This study therefore sought to investigate how different levels of urbanization affect Aedes aegypti populations and modulate population structure in this species with the aid of wing geometric morphometrics.

METHODS

Specimens were collected from eleven locations in three areas with distinct levels of urbanization in the city of São Paulo, Brazil: conserved, intermediate and urbanized. The right wings of female mosquitoes collected were removed, and photographed and digitized. Canonical variate analysis and Mahalanobis distance were used to investigate the degree of wing-shape dissimilarity among populations. Thin-plate splines were calculated by regression analysis of Canonical Variation Analysis scores against wing-shape variation, and a cross-validated reclassification was performed for each individual; a neighbor-joining tree was then constructed.

RESULTS

Metapopulation and individual population analysis showed a clear segregation pattern in the Canonical Variation Analysis. Pairwise cross-validated reclassification yielded relatively high scores considering the microgeographical scale of the study and the fact that the study populations belong to the same species. The neighbor-joining tree showed that mosquitoes in the intermediate urban area segregated in the metapopulation and individual population analyses. Our findings show significant population structuring in Aedes aegypti mosquitoes in the areas studied. This is related to the different degrees of urbanization in the areas where the specimens were collected along with their geographical location.

CONCLUSIONS

Urbanization processes in the study areas appear to play an important role in microevolutionary processes triggered by man-made modifications in the environment, resulting in a previously unknown population structuring pattern of major epidemiological importance.

Avaliação comparativa da eficiência de armadilhas para a captura e coleta de Aedes aegypti em condições de campo

Resumo Introdução Estudos que aperfeiçoam e/ou aferem a capacidade de armadilhas na detecção de vetores auxiliam sobremaneira o processo de controle das doenças causadas por eles. Objetivo Objetivou-se comparar quatro tipos de armadilhas para captura/coleta de A. aegypti em condições de campo e avaliar a influência da temperatura e precipitação na eficiência destas armadilhas. Método Armadilhas ovitrampas (papel-filtro e paleta), mosquitéricas e MosquiTRAP ® foram instaladas em 10 quarteirões, que recebiam, em cada uma de suas faces, um tipo destas armadilhas. Foram calculados índices entomológicos qualitativos e quantitativos para todas as armadilhas. Resultados A armadilha mosquitérica apresentou o menor índice de positividade (3%). Apenas os índices IPAaegypti e IDAaegypti demonstraram relação positiva com a temperatura e a precipitação, respectivamente. As armadilhas ovitrampas tiveram até 6,6 vezes maiores chances de positividade para A. aegypti quando comparadas com as MosquiTRAP ®, sem diferença significante entre os substratos papel-filtro e paleta. Conclusão As armadilhas ovitrampas apresentaram os melhores índices para serem utilizadas na vigilância do A. aegypti. É recomendado de forma imperativa o uso do papel-filtro como substrato para oviposição, pelo seu menor custo, maior facilidade de confecção, transporte e armazenamento, além da melhor visibilidade dos ovos depositados.

Analysis of the spatial distribution of scientific publications regarding vector-borne diseases related to climate variability in South America

Most vector-borne diseases exhibit a distinct seasonal pattern, which clearly suggests that they are weather sensitive. Rainfall, temperature, and other climate variables affect in many ways both the vectors and the pathogens they transmit. Likewise, climate can be determinant in outbreaks incidence. A growing number of studies have provided evidence indicating the effects of climate variability on vector-borne diseases. However, oftentimes, the different diseases and regions are not uniformly represented, scarcity or lack of publications in some countries is common. The objectives of this work were to analyze the distribution and abundance of publications on vector-borne diseases associated with climate variability in South America, identify those works that conducted a geographic analysis and detect the countries where outbreaks occurred and the climate variables with which they were associated. A systematic review of the literature published on vector-borne diseases linked to climate variability in South America was conducted, identifying, evaluating and summarizing scientific papers. The distribution of the study areas and disease type in the publications were represented on maps. Dengue and leishmaniasis were the most studied and widely represented diseases in South America. The country with the largest number of published papers and presence of all disease types was Brazil. Outbreaks of disease were related to different climate variables. Most diseases from the publications under study occurred in equatorial and tropical climates. The disease represented by the largest number of different types of climates was dengue. The technique used in this work allowed us to determine the status of knowledge of the main diseases associated with climate variability in South America. This methodology could be improved in the future by incorporating other bibliographic sources as well as other diseases related to climate variability.

The Social and Spatial Ecology of Dengue Presence and Burden during an Outbreak in Guayaquil, Ecuador, 2012

Dengue fever, a mosquito-borne arbovirus, is a major public health concern in Ecuador. In this study, we aimed to describe the spatial distribution of dengue risk and identify local social-ecological factors associated with an outbreak of dengue fever in the city of Guayaquil, Ecuador. We examined georeferenced dengue cases (n = 4248) and block-level census data variables to identify social-ecological risk factors associated with the presence/absence and burden of dengue in Guayaquil in 2012. Local Indicators of Spatial Association (LISA), specifically Anselin’s Local Moran’s I, and Moran’s I tests were used to locate hotspots of dengue transmission, and multimodel selection was used to identify covariates associated with dengue presence and burden at the census block level. We identified significant dengue transmission hotspots near the North Central and Southern portions of Guayaquil. Significant risk factors for presence of dengue included poor housing conditions, access to paved roads, and receipt of remittances. Counterintuitive positive correlations with dengue presence were observed with several municipal services such as garbage collection and access to piped water. Risk factors for increased burden of dengue included poor housing conditions, garbage collection, receipt of remittances, and sharing a property with more than one household. Social factors such as education and household demographics were negatively correlated with increased dengue burden. These findings elucidate underlying differences with dengue presence versus burden, and suggest that vulnerability and risk maps could be developed to inform dengue prevention and control; this is information that is also relevant for emerging epidemics of chikungunya and Zika viruses.

DETERMINATION OF ENVIRONMENTAL FACTORS AFFECTING DENGUE INCIDENCE IN SLEMAN DISTRICT, YOGYAKARTA, INDONESIA

Background:

Dengue is a disease related to the environment that spreads rapidly. Prevention movement is considered ineffective; therefore, a more efficient early warning system is required. It is required strongly correlated variables to as predictor in early warning system. This study aims to identify the environmental conditions associated with dengue.

Materials and methods:

This ecological study was conducted on five sub-districts selected based on the trend of the incidence. Data land cover and elevation obtained using GIS. Climate data were obtained from Meteorology and Climatology and Geophysics Agency of Yogyakarta.

Results:

There were 1.150 dengue cases from 2008-2013 obtained from District Health Office. The spatial pattern is clustered in all sub-districts (Z-score < -2.58). There is a positive correlation between land cover and dengue (p 0.000; r 0.284) and a negative correlation between elevation areas and dengue (p 0.000; r - 0.127). Multiple Regression Test shows the effect of humidity (p 0.000) and rainfall (p 0.002) with a contribution of 13.5% - 27.4% (r² 0.135 – 0.274), while temperature has no effect in all sub-districts (p > 0.05). There is no effect of climate parameters in sporadic dengue areas (p > 0.05).

Conclusion:

It is concluded that dengue in Sleman is clustered and associated with the environment parameter, even though it does not have close correlation. High elevated and small building area is consistent with the lower dengue cases. Humidity and rainfall affect dengue, but temperature does not affect dengue.

Evaluation of sticky traps for adult Aedes mosquitoes in Malaysia: a potential monitoring and surveillance tool for the efficacy of control strategies

The present study compared the performance of sticky traps in order to identify the most effective and practical trap for capturing Aedes aegypti and Aedes albopictus mosquitoes. Three phases were conducted in the study, with Phase 1 evaluating the five prototypes (Models A, B, C, D, and E) of sticky trap release-and-recapture using two groups of mosquito release numbers (five and 50) that were released in each replicate. Similarly, Phase 2 compared the performance between Model E and the classical ovitrap that had been modified (sticky ovitrap), using five and 50 mosquito release numbers. Further assessment of both traps was carried out in Phase 3, in which both traps were installed in nine sampling grids. Results from Phase 1 showed that Model E was the trap that recaptured higher numbers of mosquitoes when compared to Models A, B, C, and D. Further assessment between Model E and the modified sticky ovitrap (known as Model F) found that Model F outperformed Model E in both Phases 2 and 3. Thus, Model F was selected as the most effective and practical sticky trap, which could serve as an alternative tool for monitoring and controlling dengue vectors in Malaysia.

Microgeographic population structuring of Aedes aegypti (Diptera: Culicidae)

Aedes aegypti is one of the species most favored by changes in the environment caused by urbanization. Its abundance increases rapidly in the face of such changes, increasing the risk of disease transmission. Previous studies have shown that mosquito species that have adapted to anthropogenic environmental changes benefit from urbanization and undergo population expansion. In light of this, we used microsatellite markers to explore how urbanization processes may be modulating Ae. aegypti populations collected from three areas with different levels of urbanization in the city of São Paulo, Brazil. Specimens were collected at eleven sites in three areas with different degrees of urbanization in the city of São Paulo: conserved, intermediate and urbanized. Ten microsatellite loci were used to characterize the populations from these areas genetically. Our findings suggest that as urbanized areas grow and the human population density in these areas increases, Ae. aegypti populations undergo a major population expansion, which can probably be attributed to the species’ adaptability to anthropogenic environmental changes. Our findings reveal a robust association between, on the one hand, urbanization processes and densification of the human population and, on the other, Ae. aegypti population structure patterns and population expansion. This indicates that this species benefits from anthropogenic effects, which are intensified by migration of the human population from rural to urban areas, increasing the risk of epidemics and disease transmission to an ever-increasing number of people.

Spatio-temporal and neighborhood characteristics of two dengue outbreaks in two arid cities of Mexico

Little is currently known about the spatial-temporal dynamics of dengue epidemics in arid areas. This study assesses dengue outbreaks that occurred in two arid cities of Mexico, Hermosillo and Navojoa, located in northern state of Sonora. Laboratory confirmed dengue cases from Hermosillo (N=2730) and Navojoa (N=493) were geocoded by residence and assigned neighborhood-level characteristics from the 2010 Mexican census. Kernel density and Space-time cluster analysis was performed to detect high density areas and space-time clusters of dengue. Ordinary Least Square regression was used to assess the changing socioeconomic characteristics of cases over the course of the outbreaks. Both cities exhibited contiguous patterns of space-time clustering. Initial areas of dissemination were characterized in both cities by high population density, high percentage of occupied houses, and lack of healthcare. Future research and control efforts in these regions should consider these space-time and socioeconomic patterns.

A Large Scale Biorational Approach Using Bacillus thuringiensis israeliensis (Strain AM65-52) for Managing Aedes aegypti Populations to Prevent Dengue, Chikungunya and Zika Transmission

Background

Aedes aegypti is a container-inhabiting mosquito and a vector of dengue, chikungunya, and Zika viruses. In 2009 several cases of autochthonous dengue transmission were reported in Key West, Florida, USA prompting a comprehensive response to control A. aegypti. In Key West, larvae of this mosquito develop in containers around human habitations which can be numerous and labor intensive to find and treat. Aerial applications of larvicide covering large areas in a short time can be an efficient and economical method to control A. aegypti. Bacillus thuringiensis israelensis (Bti) is a bacterial larvicide which is highly target specific and appropriate for wide area spraying over urban areas, but to date, there are no studies that evaluate aerial spraying of Bti to control container mosquitoes like A. aegypti.

Methodology

This paper examines the effectiveness of aerial larvicide applications using VectoBac^® WG, a commercially available Bti formulation, for A. aegypti control in an urban setting in the USA. Droplet characteristics and spray drop deposition were evaluated in Key West, Florida, USA. The mortality of A. aegypti in containers placed under canopy in an urban environment was also evaluated. Efficacy of multiple larvicide applications on adult female A. aegypti population reduction was compared between an untreated control and treatment site.

Conclusions

Droplet characteristics showed that small droplets can penetrate through dense canopy to reach small containers. VectoBac WG droplets reached small containers under heavy canopy in sufficient amounts to cause > 55% mortality on all application days and >90% mortality on 3 of 5 application days while controls had <5% mortality. Aerial applications of VectoBac WG caused significant decrease in adult female populations throughout the summer and during the 38^th week (last application) the difference in adult female numbers between untreated and treated sites was >50%. Aerial larvicide applications using VectoBac WG can cover wide areas in a short period of time and can be effective in controlling A. aegypti and reducing A. aegypti-borne transmission in urban areas similar to Key West, Florida, USA.

Mosquito populations dynamics associated with climate variations

Mosquitoes are responsible for the transmission of numerous serious pathogens. Members of the Aedes and Culex genera, which include many important vectors of mosquito-borne diseases, are highly invasive and adapted to man-made environments. They are spread around the world involuntarily by humans and are highly adapted to urbanized environments, where they are exposed to climate-related abundance drivers. We investigated Culicidae fauna in two urban parks in the city of São Paulo to analyze the correlations between climatic variables and the population dynamics of mosquitoes in these urban areas. Mosquitoes were collected monthly over one year, and sampling sufficiency was evaluated after morphological identification of the specimens. The average monthly temperature and accumulated rainfall for the collection month and previous month were used to explain climate-related abundance drivers for the six most abundant species (Aedes aegypti, Aedes albopictus, Aedes fluviatilis, Aedes scapularis, Culex nigripalpus and Culex quinquefasciatus) and then analyzed using generalized linear statistical models and the Akaike Information Criteria corrected for small samples (AICc). The strength of evidence in favor of each model was evaluated using Akaike weights, and the explanatory model power was measured by McFadden's Pseudo-R². Associations between climate and mosquito abundance were found in both parks, indicating that predictive models based on climate variables can provide important information on mosquito population dynamics. We also found that this association is species-dependent. Urbanization processes increase the abundance of a few mosquito species that are well adapted to man-made environments and some of which are important vectors of pathogens. Predictive models for abundance based on climate variables may help elucidate the population dynamics of urban mosquitoes and their impact on the risk of disease transmission, allowing better predictive scenarios to be developed and supporting the implementation of vector mosquito control strategies.

Genetic Polymorphism of Aedes albopictus Population Inferred From ND5 Gene Variabilities In Subang Jaya, Malaysia

This study was performed to establish the genetic variability of Aedes albopictus within Subang Jaya, Selangor, Malaysia, by using the nicotinamide adenine dinucleotide dehydrogenase 5 subunit (ND5) mitochondrial DNA (mtDNA) marker. A total of 90 samples were collected from 9 localities within an area of the Subang Jaya Municipality. Genetic variability was determined through the amplification and sequencing of a fragment of the ND5 gene. Eight distinct mtDNA haplotypes were identified. The evolutionary relationship of the local haplotypes alongside 28 reference strains was used to construct a phylogram, the analysis of which revealed low genetic differentiation in terms of both nucleotide and haplotype diversity. Bayesian method was used to infer the phylogenetic tree, revealing a unique relationship between local isolates. The study corroborates the reliability of ND5 to identify distinct lineages for polymorphism-based studies and supplements the existing body of knowledge regarding its genetic diversity. This in turn could potentially aid existing vector control strategies to help mitigate the risk and spread of the dengue virus.

Role of Aedes aegypti (Linnaeus) and Aedes albopictus (Skuse) in local dengue epidemics in Taiwan

BACKGROUND

Aedes mosquitoes in Taiwan mainly comprise Aedes albopictus and Ae. aegypti. However, the species contributing to autochthonous dengue spread and the extent at which it occurs remain unclear. Thus, in this study, we spatially analyzed real data to determine spatial features related to local dengue incidence and mosquito density, particularly that of Ae. albopictus and Ae. aegypti.

METHODS

We used bivariate Moran's I statistic and geographically weighted regression (GWR) spatial methods to analyze the globally spatial dependence and locally regressed relationship between (1) imported dengue incidences and Breteau indices (BIs) of Ae. albopictus, (2) imported dengue incidences and BI of Ae. aegypti, (3) autochthonous dengue incidences and BI of Ae. albopictus, (4) autochthonous dengue incidences and BI of Ae. aegypti, (5) all dengue incidences and BI of Ae. albopictus, (6) all dengue incidences and BI of Ae. aegypti, (7) BI of Ae. albopictus and human population density, and (8) BI of Ae. aegypti and human population density in 348 townships in Taiwan.

RESULTS

In the GWR models, regression coefficients of spatially regressed relationships between the incidence of autochthonous dengue and vector density of Ae. aegypti were significant and positive in most townships in Taiwan. However, Ae. albopictus had significant but negative regression coefficients in clusters of dengue epidemics. In the global bivariate Moran's index, spatial dependence between the incidence of autochthonous dengue and vector density of Ae. aegypti was significant and exhibited positive correlation in Taiwan (bivariate Moran's index = 0.51). However, Ae. albopictus exhibited positively significant but low correlation (bivariate Moran's index = 0.06). Similar results were observed in the two spatial methods between all dengue incidences and Aedes mosquitoes (Ae. aegypti and Ae. albopictus). The regression coefficients of spatially regressed relationships between imported dengue cases and Aedes mosquitoes (Ae. aegypti and Ae. albopictus) were significant in 348 townships in Taiwan. The results indicated that local Aedes mosquitoes do not contribute to the dengue incidence of imported cases. The density of Ae. aegypti positively correlated with the density of human population. By contrast, the density of Ae. albopictus negatively correlated with the density of human population in the areas of southern Taiwan. The results indicated that Ae. aegypti has more opportunities for human-mosquito contact in dengue endemic areas in southern Taiwan.

CONCLUSIONS

Ae. aegypti, but not Ae. albopictus, and human population density in southern Taiwan are closely associated with an increased risk of autochthonous dengue incidence.

A comparative analysis of three different methods for the estimation of the basic reproduction number of dengue

The basic reproduction number, R₀, is defined as the expected number of secondary cases of a disease produced by a single infection in a completely susceptible population, and can be estimated in several ways. For example, from the stability analysis of a compartmental model; through the use of the matrix of next generation, or from the final size of an epidemic, etc. In this paper we applied the method for estimating R₀ of dengue fever from the initial growth phase of an outbreak, without assuming exponential growth of cases, a common assumption in many studies. We used three different methods of calculating R₀ to compare the techniques' details and to evaluate how these techniques estimate the value of R₀ of dengue using data from the city of Ribeirão Preto (SE of Brazil) in two outbreaks. The results of the three methods are numerically different but, when we compare them using a system of differential equations developed for modeling only the first generation time, we can observe that the methods differ little in the initial growth phase. We conclude that the methods predict that dengue will spread in the city studied and the analysis of the data shows that the estimated values of R₀ have an equal pattern overtime.

Natural vertical transmission of dengue viruses in Aedes aegypti in selected sites in Cebu City, Philippines

We attempted to determine the vertical transmission of dengue virus (DENV) in Aedes aegypti in selected sites in Cebu City, Philippines. Mosquito sub-adults were collected monthly from households and the field during the wet-dry-wet season from November, 2011 to July, 2012 and were laboratory-reared to adults. Viral RNA extracts in mosquitoes were assayed by hemi-nested RT-PCR. Results showed that 62 (36.26%; n=679) out of 171 mosquito pools (n=2,871) were DENV+. The minimum infection rate (MIR) of DENV ranged from 0 in wet months to 48.22/1,000 mosquitoes in April, 2012 (mid-dry). DENVs were detected in larvae, pupae, and male and female adults, with DENV-4, DENV-3, and DENV-1, in that rank of prevalence. DENV-1 co-infected with either DENV-3 or -4 or with both in April, 2012; DENV-3 and -4 were present in both seasons. More DENV+ mosquitoes were collected from households than in field premises (p<0.001) and in the dry than in the wet season (p<0.05), with significant interaction (p<0.05) between sites and premises but no interaction between sites and seasons (p>0.05). By Generalized Linear Mixed models, the type of premises nested in sites and monthly total rainfall were significant predictors of monthly dengue cases (p<0.05) and not MIR, season, temperature, and relative humidity. Surveillance of DENV prevalence in Ae. aegypti and detecting their natural foci in the dry season provide an early warning signal of dengue outbreak.

Historical inability to control Aedes aegypti as a main contributor of fast dispersal of chikungunya outbreaks in Latin America

The arrival of chikungunya fever (CHIKF) in Latin American countries has been expected to trigger epidemics and challenge health systems. Historically considered as dengue-endemic countries, abundant Aedes aegypti populations make this region highly vulnerable to chikungunya virus (CHIKV) circulation. This review describes the current dengue and CHIKF epidemiological situations, as well as the role of uncontrolled Ae. aegypti and Aedes albopictus vectors in spreading the emerging CHIKV. Comments are included relating to the vector competence of both species and failures of surveillance and vector control measures. Dengue endemicity is a reflection of these abundant and persistent Aedes populations that are now spreading CHIKV in the Americas. This article forms part of a symposium in Antiviral Research on "Chikungunya discovers the New World."

A role for vector control in dengue vaccine programs

Development and deployment of a successful dengue virus (DENV) vaccine has confounded research and pharmaceutical entities owing to the complex nature of DENV immunity and concerns over exacerbating the risk of DENV hemorrhagic fever (DHF) as a consequence of vaccination. Thus, consensus is growing that a combination of mitigation strategies will be needed for DENV to be successfully controlled, likely involving some form of vector control to enhance a vaccine program. We present here a deterministic compartmental model to illustrate that vector control may enhance vaccination campaigns with imperfect coverage and efficacy. Though we recognize the costs and challenges associated with continuous control programs, simultaneous application of vector control methods coincident with vaccine roll out can have a positive effect by further reducing the number of human cases. The success of such an integrative strategy is predicated on closing gaps in our understanding of the DENV transmission cycle in hyperedemic locations.