The impact of temperature on the bionomics of Aedes (Stegomyia) aegypti, with special reference to the cool geographic range margins

Temporal dynamics of the egg bank of Aedes aegypti (Diptera: Culicidae) in the winter-spring transition in a temperate region

In temperate regions, the populations of Aedes aegypti (L.) (Diptera: Culicidae) remain in the egg stage during the winter. In Buenos Aires, Argentina, a temperate region in the southern limit of Ae. aegypti distribution, the start of the next reproductive season and the rate of increase of the adult population depend on the egg bank that remains after the winter. This study aimed to analyze the mortality, field-hatching, and survival of eggs exposed to field conditions representative of those that occur in nature. In addition, the post-exposure hatching response of the eggs was assessed. Four egg batches were exposed to natural conditions starting in mid-winter and were recovered progressively after 3, 6, 9, and 12 weeks. One egg batch (initial control) was not exposed in the field and remained under laboratory conditions. After the exposure period, the recovered intact, collapsed, and hatched eggs were counted. Intact eggs were immersed three times in the laboratory to study their hatching response. Progressive increases in the proportion of lost (presumably by predation), dead, and hatched eggs in successive egg batches were recorded. Field-hatching was recorded from late winter onwards. The first hatchings occurred in conditions probably not favorable to complete development into reproductive adults. A progressive decrease in live eggs was observed, with 51% of the recovered eggs alive after 12 weeks of exposure. In the laboratory, the hatching response in the first immersion was low for the initial control and for the eggs exposed for 3 weeks, and increased for successive cohorts. The results confirm that the survival of Ae. aegypti eggs in the winter-spring transition ensures persistence throughout the next favorable season in Buenos Aires City. The observed inhibition to hatch of the first batches might relate to a photoperiod-induced diapause, as observed in previous studies.

Assessing dengue risk globally using non-Markovian models

Dengue is a vector-borne disease transmitted by Aedes mosquitoes. The worldwide spread of these mosquitoes and the increasing disease burden have emphasized the need for a spatio-temporal risk map capable of assessing dengue outbreak conditions and quantifying the outbreak risk. Given that the life cycle of Aedes mosquitoes is strongly influenced by habitat temperature, numerous studies have utilized temperature-dependent development rates of these mosquitoes to construct virus transmission and outbreak risk models. In this study, we contribute to existing research by developing a mechanistic model for the mosquito life cycle that accurately captures its non-Markovian nature. Beginning with integral equations to track the mosquito population across different life cycle stages, we demonstrate how to derive the corresponding differential equations using phase-type distributions. This approach can be further applied to similar non-Markovian processes that are currently described with less accurate Markovian models. By fitting the model to data on human dengue cases, we estimate several model parameters, allowing the development of a global spatiotemporal dengue risk map. This risk model employs temperature and precipitation data to assess the environmental suitability for dengue outbreaks in a given area.

Dengue and chikungunya: future threats for Northern Europe?

Arthropod-borne viral diseases are likely to be affected by the consequences of climate change with an increase in their distribution and intensity. Among these infectious diseases, chikungunya and dengue viruses are two (re)emergent arboviruses transmitted by Aedes species mosquitoes and which have recently demonstrated their capacity for rapid expansion. They most often cause mild diseases, but they can both be associated with complications and severe forms. In Europe, following the establishment of invasive Aedes spp, the first outbreaks of autochtonous dengue and chikungunya have already occurred. Northern Europe is currently relatively spared, but climatic projections show that the conditions are permissive for the establishment of Aedes albopictus (also known as the tiger mosquito) in the coming decades. It is therefore essential to question and improve the means of surveillance in northern Europe, at the dawn of inevitable future epidemics.

Modeling and updating the occurrence of Aedes aegypti in its southern limit of distribution in South America

Aedes aegypti is the main vector of arboviruses in the world. This mosquito species is distributed from tropical to temperate regions. In Argentina, it has been reported in 20 out of 23 provinces and reaches its southernmost distribution in the world. Its distribution and persistence are affected by meteorological, demographic and environmental factors, such as temperature, precipitation, and population. The aim of this study was to update and model the occurrence of Aedes aegypti in its southern limit of distribution in Argentina. To this end, a total of 37 sites were inspected in La Pampa and Río Negro provinces. Generalized Linear Models were used to explain the occurrence of Aedes aegypti based on meteorological, environmental and demographic variables. Aedes aegypti was found in 11 cities of La Pampa province where it had not been previously reported, but was not found in any of the cities evaluated in Río Negro province. The averaged model explaining the occurrence of Aedes aegypti included the minimum temperature, precipitation and interactions between maximum temperature and precipitation as explanatory variables. Although precipitation was statistically significant, other factors such as minimum temperature are also important in modeling the occurrence of Aedes aegypti in its southernmost distribution limit.

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.

Ecological Niche and Positive Clusters of Two West Nile Virus Vectors in Ontario, Canada

West Nile virus (WNV) is a mosquito-borne pathogen associated with uncommon but severe neurological complications in humans, especially among the elderly and immune-compromised. In Northeastern North America, the Culex pipiens/restuans complex and Aedes vexans are the two principal vector mosquito species/species groups of WNV. Using a 10-year surveillance dataset of WNV vector captures at 118 sites across an area of 40,000 km2 in Eastern Ontario, Canada, the ecological niches of Cx. pipiens/restuans and Aedes vexans were modeled by random forest analysis. Spatiotemporal clusters of WNV-positive mosquito pools were identified using Kulldorf's spatial scan statistic. The study region encompasses land cover types and climate representative of highly populated Southeastern Canada. We found highest vector habitat suitability in the eastern half of the study area, where temperatures are generally warmer (variable importance > 0.40) and residential and agricultural cropland cover is more prominent (variable importance > 0.25). We found spatiotemporal clusters of high WNV infection rates around the city of Ottawa in both mosquito vector species. These results support the previous literature in the same region and elsewhere suggesting areas surrounding highly populated areas are also high-risk areas for vector-borne zoonoses such as the WNV.

PICTUREE-Aedes: A Web Application for Dengue Data Visualization and Case Prediction

Dengue fever remains a significant public health concern in many tropical and subtropical countries, and there is still a need for a system that can effectively combine global risk assessment with timely incidence forecasting. This research describes an integrated application called PICTUREE-Aedes, which can collect and analyze dengue-related data, display simulation results, and forecast outbreak incidence. PICTUREE-Aedes automatically updates global temperature and precipitation data and contains historical records of dengue incidence (1960-2012) and Aedes mosquito occurrences (1960-2014) in its database. The application utilizes a mosquito population model to estimate mosquito abundance, dengue reproduction number, and dengue risk. To predict future dengue outbreak incidence, PICTUREE-Aedes applies various forecasting techniques, including the ensemble Kalman filter, recurrent neural network, particle filter, and super ensemble forecast, which are all based on user-entered case data. The PICTUREE-Aedes' risk estimation identifies favorable conditions for potential dengue outbreaks, and its forecasting accuracy is validated by available outbreak data from Cambodia.

The influence of weather on the population dynamics of common mosquito vector species in the Canadian Prairies

BACKGROUND

Mosquito seasonal activity is largely driven by weather conditions, most notably temperature, precipitation, and relative humidity. The extent by which these weather variables influence activity is intertwined with the animal's biology and may differ by species. For mosquito vectors, changes in weather can also alter host-pathogen interactions thereby increasing or decreasing the burden of disease.

METHODS

In this study, we performed weekly mosquito surveillance throughout the active season over a 2-year period in Manitoba, Canada. We then used Generalized Linear Mixed Models (GLMMs) to explore the relationships between weather variables over the preceding 2 weeks and mosquito trap counts for four of the most prevalent vector species in this region: Oc. dorsalis, Ae. vexans, Cx. tarsalis, and Cq. perturbans.

RESULTS

More than 265,000 mosquitoes were collected from 17 sampling sites throughout Manitoba in 2020 and 2021, with Ae. vexans the most commonly collected species followed by Cx. tarsalis. Aedes vexans favored high humidity, intermediate degree days, and low precipitation. Coquillettidia perturbans and Oc. dorsalis activity increased with high humidity and high rainfall, respectively. Culex tarsalis favored high degree days, with the relationship between number of mosquitoes captured and precipitation showing contrasting patterns between years. Minimum trapping temperature only impacted Ae. vexans and Cq. perturbans trap counts.

CONCLUSIONS

The activity of all four mosquito vectors was affected by weather conditions recorded in the 2 weeks prior to trapping, with each species favoring different conditions. Although some research has been done to explore the relationships between temperature/precipitation and Cx. tarsalis in the Canadian Prairies, to our knowledge this is the first study to investigate other commonly found vector species in this region. Overall, this study highlights how varying weather conditions can impact mosquito activity and in turn species-specific vector potential.

A systematic review and meta-analysis of the effects of temperature on the development and survival of the Aedes mosquito

Introduction

The Aedes mosquito species, which are the vectors for the transmission of the dengue virus (DENV) to humans, are becoming increasingly susceptible to the formidable effects of influential factors, especially temperature. However, there are still very few studies that have systematically reviewed the existing literature. Hence, in the present study, a systematic literature review and meta-analysis was conducted into the effects of temperature on dengue vectors.

Method

Several research methodologies were incorporated into the current study, and a review was carried out using PRISMA as a guide. The publications for this study were chosen from two prominent databases, Scopus and Web of Science. All of the studies were assessed, reviewed, and evaluated independently by two reviewers. The meta-analysis tool, Review Manager (RevMan Copenhagen Version 5.4.1), was used to record the extracted data for the meta-analysis. Moran's I ² and a funnel plot were utilized to measure heterogeneity, and publication bias was investigated. A 95% confidence interval (CI) and overall risk difference (RD) were estimated using a random-effects model.

Result and discussion

As a consequence of the search efforts, a total of 46 articles were selected for inclusion in the systematic review and meta-analysis. This review was divided into five major themes, based on a thematic analysis: (i) hatching rate, (ii) development time, (iii) longevity, (iv) survival rate, and (v) wing morphology. In addition, the development time, survival rate, and wing morphology revealed significantly higher risk differences between the maximum and minimum temperatures (RD: 0.26, 95% CI: 0.16, 0.36; p = < 0.00001; RD: 0.10, 95% CI: 0.05, 0.14; p < 0.0001; and RD: 0.07, 95% CI: 0.02, 0.12; p = 0.006, respectively). This study makes several substantial contributions to the body of knowledge and to practical applications. Finally, a number of recommendations are made at the conclusion of this research for the future reference of researchers.

Close-kin mark-recapture methods to estimate demographic parameters of mosquitoes

Close-kin mark-recapture (CKMR) methods have recently been used to infer demographic parameters such as census population size and survival for fish of interest to fisheries and conservation. These methods have advantages over traditional mark-recapture methods as the mark is genetic, removing the need for physical marking and recapturing that may interfere with parameter estimation. For mosquitoes, the spatial distribution of close-kin pairs has been used to estimate mean dispersal distance, of relevance to vector-borne disease transmission and novel biocontrol strategies. Here, we extend CKMR methods to the life history of mosquitoes and comparable insects. We derive kinship probabilities for mother-offspring, father-offspring, full-sibling and half-sibling pairs, where an individual in each pair may be a larva, pupa or adult. A pseudo-likelihood approach is used to combine the marginal probabilities of all kinship pairs. To test the effectiveness of this approach at estimating mosquito demographic parameters, we develop an individual-based model of mosquito life history incorporating egg, larva, pupa and adult life stages. The simulation labels each individual with a unique identification number, enabling close-kin relationships to be inferred for sampled individuals. Using the dengue vector Aedes aegypti as a case study, we find the CKMR approach provides unbiased estimates of adult census population size, adult and larval mortality rates, and larval life stage duration for logistically feasible sampling schemes. Considering a simulated population of 3,000 adult mosquitoes, estimation of adult parameters is accurate when ca. 40 adult females are sampled biweekly over a three month period. Estimation of larval parameters is accurate when adult sampling is supplemented with ca. 120 larvae sampled biweekly over the same period. The methods are also effective at detecting intervention-induced increases in adult mortality and decreases in population size. As the cost of genome sequencing declines, CKMR holds great promise for characterizing the demography of mosquitoes and comparable insects of epidemiological and agricultural significance.

dynamAedes: a unified modelling framework for invasive Aedes mosquitoes

Mosquito species belonging to the genus Aedes have attracted the interest of scientists and public health officers because of their capacity to transmit viruses that affect humans. Some of these species were brought outside their native range by means of trade and tourism and then colonised new regions thanks to a unique combination of eco-physiological traits. Considering mosquito physiological and behavioural traits to understand and predict their population dynamics is thus a crucial step in developing strategies to mitigate the local densities of invasive Aedes populations. Here, we synthesised the life cycle of four invasive Aedes species (Ae. aegypti, Ae. albopictus, Ae. japonicus and Ae. koreicus) in a single multi-scale stochastic modelling framework which we coded in the R package dynamAedes. We designed a stage-based and time-discrete stochastic model driven by temperature, photo-period and inter-specific larval competition that can be applied to three different spatial scales: punctual, local and regional. These spatial scales consider different degrees of spatial complexity and data availability by accounting for both active and passive dispersal of mosquito species as well as for the heterogeneity of the input temperature data. Our overarching aim was to provide a flexible, open-source and user-friendly tool rooted in the most updated knowledge on the species' biology which could be applied to the management of invasive Aedes populations as well as to more theoretical ecological inquiries.

How do i bite thee? let me count the ways: Exploring the implications of individual biting habits of Aedes aegypti for dengue transmission

In models of mosquito-borne transmission, the mosquito biting rate is an influential parameter, and understanding the heterogeneity of the process of biting is important, as biting is usually assumed to be relatively homogeneous across individuals, with time-between-bites described by an exponentially distributed process. However, these assumptions have not been addressed through laboratory experimentation. We experimentally investigated the daily biting habits of Ae. aegypti at three temperatures (24°C, 28°C, and 32°C) and determined that there was individual heterogeneity in biting habits (number of bites, timing of bites, etc.). We further explored the consequences of biting heterogeneity using an individual-based model designed to examine whether a particular biting profile determines whether a mosquito is more or less likely to 1) become exposed given a single index case of dengue (DENV) and 2) transmit to a susceptible human individual. Our experimental results indicate that there is heterogeneity among individuals and among temperature treatments. We further show that this results in altered probabilities of transmission of DENV to and from individual mosquitoes based on biting profiles. While current model representation of biting may work under some conditions, it might not uniformly be the best fit for this process. Our data also confirm that biting is a non-monotonic process with temperatures around 28°C being optimum.

Temporal and spatial patterns of dengue geographical distribution in Jeddah, Saudi Arabia

INTRODUCTION

Dengue fever disease is affected by many scoioeconomic and enviromental factors throughout endemic areas globally. These factors contribute to increase the incidence of endemic dengue endemic in Jeddah, Saudi Arabia.

OBJECTIVES

This study aimed to investigate the distribution and spatial patterns of dengue fever cases in Jeddah, and to determine if there is an association between dengue fever and the following environmental factors: temperature, humidity, land cover, climate, rainfall, epicenter of reproduction, and socioeconomic factors.

METHODS

A descriptive and analytical cross-sectional study was conducted in Jeddah in 2020. The study included all reported suspected and confirmed dengue cases. The sample size was 1458 cases. Data were obtained from the Dengue Active Surveillance System and the confirmed cases were geo-distributed in areas by QGIS. All significant variables were included in the logistic regression table.

RESULTS

The majority (61.9 %) were suspected cases and 38.1 % confirmed cases. The majority of the cases were male. The highest spatial distribution was in the middle of Jeddah and the lowest in the south. The highest temporal distribution for confirmed cases was in June, and for suspected cases in December. Age, gender, occupation, and area were all significantly associated with the dengue reported cases. Most all the enviromental factors were not statistically significant.

CONCLUSION

The study showed three clusters of dengue fever and infection concentrated in the middle and east of Jeddah. The lack of investigation in the environmental factors regarding the dengue distribution and its impact on the population area has to be taken seriously and dengue intervention programs should be implemented to reduce the endemic dengue in Jeddah.

Winter survival of Aedes aegypti (Diptera: Culicidae) eggs at its southern limit distribution

Aedes aegypti (L.) (Diptera: Culicidae) survives in the egg stage under unfavorable environmental conditions. In this study, we assessed the survival of Ae. aegypti eggs under natural winter conditions as an overwintering mechanism. To address this, field collected eggs (from Buenos Aires city) were exposed for three months during the winter season in three sites of Santa Rosa and General Acha (La Pampa province, Argentina). Eggs survival and hatching response were analyzed considering two factors (site of exposure and time of oviposition). Of the 1397 analyzed eggs, 936 (67%) were viable at the end of the study. Egg survival showed to be high in all sites (between 53% and 84%), except in one site of Santa Rosa. Also, eggs survival was higher in eggs laid in May (94%) (late-fall) as compared to those laid in March (61%) and April (56%) (early- and mid-fall respectively). Eggs hatching response was only affected by the time of oviposition, being lower for eggs laid in May (33%) as compared to March (38%) and April (50%). These results provide information regarding the winter resistance of Ae. aegypti at the limit of its distribution in temperate regions. Given the high percentages of survival found in this study, we consider that the low winter temperatures would not be a limitation for its establishment in southern areas.

Climate variability and Aedes vector indices in the southern Philippines: An empirical analysis

Background

Vector surveillance is an essential public health tool to aid in the prediction and prevention of mosquito borne diseases. This study compared spatial and temporal trends of vector surveillance indices for Aedes vectors in the southern Philippines, and assessed potential links between vector indices and climate factors.

Methods

We analysed routinely collected larval and pupal surveillance data from residential areas of 14 cities and 51 municipalities during 2013–2018 (House, Container, Breteau and Pupal Indices), and used linear regression to explore potential relationships between vector indices and climate variables (minimum temperature, maximum temperature and precipitation).

Results

We found substantial spatial and temporal variation in monthly Aedes vector indices between cities during the study period, and no seasonal trend apparent. The House (HI), Container (CI) and Breteau (BI) Indices remained at comparable levels across most surveys (mean HI = 15, mean CI = 16, mean BI = 24), while the Pupal Productivity Index (PPI) was relatively lower in most months (usually below 5) except for two main peak periods (mean = 49 overall). A small proportion of locations recorded high values across all entomological indices in multiple surveys. Each of the vector indices were significantly correlated with one or more climate variables when matched to data from the same month or the previous 1 or 2 months, although the effect sizes were small. Significant associations were identified between minimum temperature and HI, CI and BI in the same month (R2 = 0.038, p = 0.007; R2 = 0.029, p = 0.018; and R2 = 0.034, p = 0.011, respectively), maximum temperature and PPI with a 2-month lag (R2 = 0.031, p = 0.032), and precipitation and HI in the same month (R2 = 0.023, p = 0.04).

Conclusions

Our findings indicated that larval and pupal surveillance indices were highly variable, were regularly above the threshold for triggering vector control responses, and that vector indices based on household surveys were weakly yet significantly correlated with city-level climate variables. We suggest that more detailed spatial and temporal analyses of entomological, climate, socio-environmental and Aedes-borne disease incidence data are necessary to ascertain the most effective use of entomological indices in guiding vector control responses, and reduction of human disease risk.

Deep learning models for forecasting dengue fever based on climate data in Vietnam

Background

Dengue fever (DF) represents a significant health burden in Vietnam, which is forecast to worsen under climate change. The development of an early-warning system for DF has been selected as a prioritised health adaptation measure to climate change in Vietnam.

Objective

This study aimed to develop an accurate DF prediction model in Vietnam using a wide range of meteorological factors as inputs to inform public health responses for outbreak prevention in the context of future climate change.

Methods

Convolutional neural network (CNN), Transformer, long short-term memory (LSTM), and attention-enhanced LSTM (LSTM-ATT) models were compared with traditional machine learning models on weather-based DF forecasting. Models were developed using lagged DF incidence and meteorological variables (measures of temperature, humidity, rainfall, evaporation, and sunshine hours) as inputs for 20 provinces throughout Vietnam. Data from 1997–2013 were used to train models, which were then evaluated using data from 2014–2016 by Root Mean Square Error (RMSE) and Mean Absolute Error (MAE).

Results and discussion

LSTM-ATT displayed the highest performance, scoring average places of 1.60 for RMSE-based ranking and 1.95 for MAE-based ranking. Notably, it was able to forecast DF incidence better than LSTM in 13 or 14 out of 20 provinces for MAE or RMSE, respectively. Moreover, LSTM-ATT was able to accurately predict DF incidence and outbreak months up to 3 months ahead, though performance dropped slightly compared to short-term forecasts. To the best of our knowledge, this is the first time deep learning methods have been employed for the prediction of both long- and short-term DF incidence and outbreaks in Vietnam using unique, rich meteorological features.

Conclusion

This study demonstrates the usefulness of deep learning models for meteorological factor-based DF forecasting. LSTM-ATT should be further explored for mitigation strategies against DF and other climate-sensitive diseases in the coming years.

Dengue fever (DF) represents a significant health burden worldwide and in Vietnam, which is forecast to worsen under climate change. The development of an early-warning system for DF has been selected as a prioritised health adaptation measure to climate change in Vietnam. This study aimed to use deep learning models to develop a prediction model of DF rates in Vietnam using a wide range of climate factors as input variables to inform public health responses for outbreak prevention in the context of future climate change. The study found that LSTM-ATT outperformed competing models, scoring average places of 1.60 for RMSE-based ranking and 1.90 for MAE-based ranking. Notably, it was able to forecast DF incidence better than LSTM in 12 or 14 out of 20 provinces for MAE or RMSE, respectively. Moreover, LSTM-ATT was able to accurately predict DF incidence and outbreaks up to 3 months ahead, though performance dropped slightly compared to short-term forecasts. This is the first time deep learning methods have been employed for the prediction of both long- and short-term DF incidence and outbreaks in Vietnam using unique, rich climate features, and it demonstrates the usefulness of deep learning models for climate-based DF forecasting.

Association between densities of adult and immature stages of Aedes aegypti mosquitoes in space and time: implications for vector surveillance

BACKGROUND

Mosquito control is currently the main tool available to contain the spread of several arboviruses in Brazil. We have evaluated the association between entomological surveys of female adult Aedes aegypti and the Breteau index (BI) in space and time in a hyperendemic area, and compared the human resources costs required to measure each of these indicators.

METHODS

Entomological surveys were conducted between 2016 and 2019 in Vila Toninho, a neighborhood in the city of São José do Rio Preto, Brazil. Monthly records of collected mosquito specimens were made and then grouped by season.

RESULTS

Our findings showed that adult and immature mosquitoes are more related in time than in space, possibly due to differences in their habitats or in climate variables. Bayesian temporal modeling revealed that an increase in 1 standard deviation in the BI was associated with a 27% increase in the number of adult female mosquitoes when adjusted for climatic conditions. The cost of entomological surveys of adult mosquitoes was found to be 83% lower than the cost of determining the BI when covering the same geographic area.

CONCLUSIONS

For fine-scale assessments, a simple measure of adult Ae. aegypti abundance may be more realistic than aquatic indicators, but the adult indices are not necessarily the only reliable measure. Surveying adult female mosquitoes has significant potential for optimizing vector control strategies because, unlike the BI, this tool provides an effective indicator for micro-areas within an urban region. It should be noted that the results of the present study may be due to specific features of of the study area, and future studies should analyze whether the patterns found in the study neighborhood are also found in other regions.

Effects of land use and weather on the presence and abundance of mosquito-borne disease vectors in a urban and agricultural landscape in Eastern Ontario, Canada

Weather and land use can significantly impact mosquito abundance and presence, and by consequence, mosquito-borne disease (MBD) dynamics. Knowledge of vector ecology and mosquito species response to these drivers will help us better predict risk from MBD. In this study, we evaluated and compared the independent and combined effects of weather and land use on mosquito species occurrence and abundance in Eastern Ontario, Canada. Data on occurrence and abundance (245,591 individuals) of 30 mosquito species were obtained from mosquito capture at 85 field sites in 2017 and 2018. Environmental variables were extracted from weather and land use datasets in a 1-km buffer around trapping sites. The relative importance of weather and land use on mosquito abundance (for common species) or occurrence (for all species) was evaluated using multivariate hierarchical statistical models. Models incorporating both weather and land use performed better than models that include weather only for approximately half of species (59% for occurrence model and 50% for abundance model). Mosquito occurrence was mainly associated with temperature whereas abundance was associated with precipitation and temperature combined. Land use was more often associated with abundance than occurrence. For most species, occurrence and abundance were positively associated with forest cover but for some there was a negative association. Occurrence and abundance of some species (47% for occurrence model and 88% for abundance model) were positively associated with wetlands, but negatively associated with urban (Culiseta melanura and Anopheles walkeri) and agriculture (An. quadrimaculatus, Cs. minnesotae and An. walkeri) environments. This study provides predictive relationships between weather, land use and mosquito occurrence and abundance for a wide range of species including those that are currently uncommon, yet known as arboviruses vectors. Elucidation of these relationships has the potential to contribute to better prediction of MBD risk, and thus more efficiently targeted prevention and control measures.

Imported Dengue Case Numbers and Local Climatic Patterns Are Associated with Dengue Virus Transmission in Florida, USA

Aedes aegypti mosquitoes are the main vector of dengue viruses globally and are present throughout much of the state of Florida (FL) in the United States of America. However, local transmission of dengue viruses in FL has mainly occurred in the southernmost counties; specifically Monroe and Miami-Dade counties. To get a better understanding of the ecologic risk factors for dengue fever incidence throughout FL, we collected and analyzed numerous environmental factors that have previously been connected to local dengue cases in disease-endemic regions. We analyzed these factors for each county-year in FL, between 2009–2019, using negative binomial regression. Monthly minimum temperature of 17.5–20.8 °C, an average temperature of 26.1–26.7 °C, a maximum temperature of 33.6–34.7 °C, rainfall between 11.4–12.7 cm, and increasing numbers of imported dengue cases were associated with the highest risk of dengue incidence per county-year. To our knowledge, we have developed the first predictive model for dengue fever incidence in FL counties and our findings provide critical information about weather conditions that could increase the risk for dengue outbreaks as well as the important contribution of imported dengue cases to local establishment of the virus in Ae. aegypti populations.

Trade-off between climatic and human population impacts on Aedes aegypti life history shapes its geographic distribution

The annual death statistics due to vector-borne diseases transmitted by Aedes mosquitoes cause a still growing concern for the public health in the affected regions. An improved understanding of how climatic and population changes impact the spread of Aedes aegypti will help estimate the future populations exposure and vulnerability, and is essential to the improvement of public health preparedness. We apply an empirically well-investigated process-based mathematical model based on the life cycle of the mosquito to assess how climate scenarios (Representative Concentration Pathways (RCP)) and population scenarios (Shared Socioeconomic Pathways (SSP)) will affect the growth and potential distribution of this mosquito in China. Our results show that the risk area is predicted to expand considerably, increasing up to 21.46% and 24.75% of China's land area in 2050 and 2070, respectively, and the new added area lies mainly in the east and center of China. The population in the risk area grows substantially up to 2050 and then drops down steadily. However, these predicted changes vary noticeably among different combinations between RCPs and SSPs with the RCP2.6*SSP4 yielding the most favorable scenario in 2070, representing approximately 14.11% of China's land area and 113 cities at risk, which is slightly lower compared to 2019. Our results further reveal that there is a significant trade-off between climatic and human population impacts on the spreading of Aedes aegypti, possibly leading to an overestimation (underestimation) in sparsely (densely) populated areas if the populations impact on the mosquito's life history is unaccounted for. These results suggest that both climate and population changes are crucial factors in the formation of the populations exposure to Aedes-borne virus transmission in China, however, a reduced population growth rate may slow down the spread of this mosquito by effectively counteracting the climate warming impacts.

Aedes albopictus life table: environment, food, and age dependence survivorship and reproduction in a tropical area

Background

Environmental conditions affect the biology of mosquito vectors. Aedes albopictus is a major vector of many important diseases including dengue, Zika, and chikungunya in China. Understanding the development, fecundity, and survivorship of Ae. albopictus mosquitoes in different environmental conditions is beneficial for the implementation of effective vector control measures.

Methods

Aedes albopictus larval and adult life-table experiments were conducted under natural conditions in indoor, half-shaded, and fully shaded settings, simulating the three major habitat types in Hainan Province, a tropical island in the South China Sea. Temperature, humidity, and light intensity were recorded daily. Larval rearing used habitat water and tap water, with and without additional artificial food. Development time, survivorship, pupation rate, and adult emergence rates were monitored. Adult mosquito survivorship and fecundity were monitored daily and reproductive rates were determined, and age-dependent survivorship and reproduction were analyzed.

Results

The pupation time and male and female emergence times were significantly shorter in indoor conditions than in shaded and half-shaded conditions for both tap water with added food and habitat water with added food groups. For habitat water with added food, the shaded environment had the lowest pupation rate among the settings. For tap water with added food group, the shaded environment had the lowest pupation rate. The mean survival time of females was 27.3 ± 0.8 days in the indoor condition, which was significantly longer than that in the half-shaded (18.4 ± 0.6 days) and shaded (13.8 ± 1.2 days) conditions. Adult mortality was age-dependent, and the rate of change in mortality with age was not significantly different among different environmental conditions. The mean net replacement rate (R₀) of female mosquitoes showed no significant difference among the three conditions, whereas the per capita intrinsic growth rate (r) in the shaded condition was 42.0% and 20.4% higher than that in the indoor and half-shaded conditions, respectively. Female daily egg mass was also age-dependent in all the settings, decaying exponentially with age.

Conclusions

Our results imply that half-shaded conditions are likely the best natural condition for adult emergence and female reproduction, and food supply is crucial for larval development and pupation. The results provide new avenues for integrated mosquito management in indoor and outdoor areas, especially in half-shaded areas.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-05081-x.

Predictive model for microclimatic temperature and its use in mosquito population modeling

Mosquitoes transmit several infectious diseases that pose significant threat to human health. Temperature along with other environmental factors at breeding and resting locations play a role in the organismal development and abundance of mosquitoes. Accurate analysis of mosquito population dynamics requires information on microclimatic conditions at breeding and resting locations. In this study, we develop a regression model to characterize microclimatic temperature based on ambient environmental conditions. Data were collected by placing sensor loggers at resting and breeding locations such as storm drains across Houston, TX. Corresponding weather data was obtained from National Oceanic and Atmospheric Administration website. Features extracted from these data sources along with contextual information on location were used to develop a Generalized Linear Model for predicting microclimate temperatures. We also analyzed mosquito population dynamics for Aedes albopictus under ambient and microclimatic conditions using system dynamic (SD) modelling to demonstrate the need for accurate microclimatic temperatures in population models. The microclimate prediction model had an R² value of ~ 95% and average prediction error of ~ 1.5 °C indicating that microclimate temperatures can be reliably estimated from the ambient environmental conditions. SD model analysis indicates that some microclimates in Texas could result in larger populations of juvenile and adult Aedes albopictus mosquitoes surviving the winter without requiring dormancy.

Household-level risk factors for Aedes aegypti pupal density in Guayaquil, Ecuador

Background

Vector-borne diseases are a major cause of disease burden in Guayaquil, Ecuador, especially arboviruses spread by Aedes aegypti mosquitoes. Understanding which household characteristics and risk factors lead to higher Ae. aegypti densities and consequent disease risk can help inform and optimize vector control programs.

Methods

Cross-sectional entomological surveys were conducted in Guayaquil between 2013 and 2016, covering household demographics, municipal services, potential breeding containers, presence of Ae. aegypti larvae and pupae, and history of using mosquito control methods. A zero-truncated negative binomial regression model was fitted to data for estimating the household pupal index. An additional model assessed the factors of the most productive breeding sites across all of the households.

Results

Of surveyed households, 610 satisfied inclusion criteria. The final household-level model found that collection of large solid items (e.g., furniture and tires) and rainfall the week of and 2 weeks before collection were negatively correlated with average pupae per container, while bed canopy use, unemployment, container water volume, and the interaction between large solid collection and rainfall 2 weeks before the sampling event were positively correlated. Selection of these variables across other top candidate models with ∆AICc < 1 was robust, with the strongest effects from large solid collection and bed canopy use. The final container-level model explaining the characteristics of breeding sites found that contaminated water is positively correlated with Ae. aegypti pupae counts while breeding sites composed of car parts, furniture, sewerage parts, vases, were all negatively correlated.

Conclusions

Having access to municipal services like bulky item pickup was effective at reducing mosquito proliferation in households. Association of bed canopy use with higher mosquito densities is unexpected, and may be a consequence of large local mosquito populations or due to limited use or effectiveness of other vector control methods. The impact of rainfall on mosquito density is multifaceted, as it may both create new habitat and “wash out” existing habitat. Providing services and social/technical interventions focused on monitoring and eliminating productive breeding sites is important for reducing aquatic-stage mosquito densities in households at risk for Ae. aegypti-transmitted diseases.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04913-0.

Comparative Study on the Thermal Performance of Three Aedes aegypti (Diptera: Culicidae) Populations From Argentina

The distribution of Aedes aegypti (L.) (Diptera: Culicidae) is expanding towards colder regions, which could be aided by an adaptation of the immature stages to the local thermal conditions. This study aimed to assess the developmental success at different temperatures in three populations of Ae. aegypti located across a climate gradient in Argentina. Survival to the adult stage, development time, and wing length at 14, 18.5 and 24°C were compared among three populations of Argentina: Resistencia in the subtropical region, and Buenos Aires and San Bernardo in the temperate region. Survival was similar between populations and equal to or higher than 69%, and increased at higher temperatures within the studied range. Development times were similar between populations. A negative effect of temperature was observed and the reduction of development time at increasing temperatures was stronger for males than for females. Wing lengths were negatively affected by increasing temperatures, and the reduction of wing length was stronger for females than for males. Also, the reduction of wing lengths with temperature was stronger for San Bernardo and Resistencia than for Buenos Aires, and differences between sexes were larger for Resistencia than for Buenos Aires or San Bernardo. Although the results do not evidence differences in survival and development time between temperate and tropical populations, the three populations have a higher tolerance to low temperatures than the populations from other regions.

Effect of Parental Photoperiod on Body Size and Developmental Time of Aedes aegypti (Diptera: Culicidae) in Buenos Aires City

Many insects use photoperiod as a signal to anticipate upcoming unfavorable conditions. Photoperiod sensitivity may be a relevant factor in Aedes (Stegomyia) aegypti (L.) populations at the cool margins of the species' range, where winter conditions have a strong effect on population dynamics. In this study, we evaluated the effect of parental photoperiod on preimaginal survival and developmental time, and on wing length for the first generation of Ae. aegypti from a temperate region (Buenos Aires City, Argentina). Our experiment started with eggs from parents exposed to short-day (SD; 10:14 [L:D]) or long-day (LD; 14:10 [L:D]) photoperiods during their entire life span. Eggs were stored under the same photoperiod (SD or LD) as their parents for 91 d, until immersion. After hatching, larvae were reared until adult emergence in thermal baths at one of two constant temperatures (17 or 23°C), at a photoperiod of 12:12 (L:D) h and fed ad libitum. Survival from larva I to adult emergence was not affected either by parental photoperiod or rearing temperature. At a rearing temperature of 23°C, female offspring from the SD parental photoperiod developed faster and had shorter wings compared with those from the LD parental photoperiod. No effect of parental photoperiod was observed on female offspring reared at 17°C. In male offspring, parental photoperiod had no effect on developmental time and wing length, independently of the rearing temperature. Results indicate that the parental photoperiod may affect some offspring traits. This effect may be a characteristic of Ae. aegypti populations in temperate regions to deal with the winter conditions.

The ecophysiological plasticity of Aedes aegypti and Aedes albopictus concerning overwintering in cooler ecoregions is driven by local climate and acclimation capacity

Aedes aegypti and Aedes albopictus transmit diseases such as dengue, and are of major public health concern. Driven by climate change and global trade/travel both species have recently spread to new tropic/subtropic regions and Ae. albopictus also to temperate ecoregions. The capacity of both species to adapt to new environments depends on their ecophysiological plasticity, which is the width of functional niches where a species can survive. Mechanistic distribution models often neglect to incorporate ecophysiological plasticity especially in regards to overwintering capacity in cooler habitats. To portray the ecophysiological plasticity concerning overwintering capability, we conducted temperature experiments with multiple populations of both species originating from an altitudinal gradient in South Asia and tested as follows: the cold tolerance of eggs (-2 °C- 8 days and - 6 °C- 2 days) without and with an experimental winter onset (acclimation: 10 °C- 60 days), differences between a South Asian and a European Ae. albopictus population and the temperature response in life cycles (13 °C, 18 °C, 23 °C, 28 °C). Ecophysiological plasticity in overwintering capacity in Ae. aegypti is high in populations originating from low altitude and in Ae. albopictus populations from high altitude. Overall, ecophysiological plasticity is higher in Ae. albopictus compared to Ae. aegypti. In both species acclimation and in Ae. albopictus temperate continental origin had a huge positive effect on survival. Our results indicate that future mechanistic prediction models can include data on winter survivorship of both, tropic and subtropic Ae. aegypti, whereas for Ae. albopictus this depends on the respective temperate, tropical region the model is focusing on. Future research should address cold tolerance in multiple populations worldwide to evaluate the full potential of the ecophysiological plasticity in the two species. Furthermore, we found that Ae. aegypti can survive winter cold especially when acclimated and will probably further spread to colder ecoregions driven by climate change.

Human-Mosquito Contact: A Missing Link in Our Understanding of Mosquito-Borne Disease Transmission Dynamics

Despite the critical role that contact between hosts and vectors, through vector bites, plays in driving vector-borne disease (VBD) transmission, transmission risk is primarily studied through the lens of vector density and overlooks host-vector contact dynamics. This review article synthesizes current knowledge of host-vector contact with an emphasis on mosquito bites. It provides a framework including biological and mathematical definitions of host-mosquito contact rate, blood-feeding rate, and per capita biting rates. We describe how contact rates vary and how this variation is influenced by mosquito and vertebrate factors. Our framework challenges a classic assumption that mosquitoes bite at a fixed rate determined by the duration of their gonotrophic cycle. We explore alternative ecological assumptions based on the functional response, blood index, forage ratio, and ideal free distribution within a mechanistic host-vector contact model. We highlight that host-vector contact is a critical parameter that integrates many factors driving disease transmission. A renewed focus on contact dynamics between hosts and vectors will contribute new insights into the mechanisms behind VBD spread and emergence that are sorely lacking. Given the framework for including contact rates as an explicit component of mathematical models of VBD, as well as different methods to study contact rates empirically to move the field forward, researchers should explicitly test contact rate models with empirical studies. Such integrative studies promise to enhance understanding of extrinsic and intrinsic factors affecting host-vector contact rates and thus are critical to understand both the mechanisms driving VBD emergence and guiding their prevention and control.

Temperature, traveling, slums, and housing drive dengue transmission in a non-endemic metropolis

Dengue is steadily increasing worldwide and expanding into higher latitudes. Current non-endemic areas are prone to become endemic soon. To improve understanding of dengue transmission in these settings, we assessed the spatiotemporal dynamics of the hitherto largest outbreak in the non-endemic metropolis of Buenos Aires, Argentina, based on detailed information on the 5,104 georeferenced cases registered during summer-autumn of 2016. The highly seasonal dengue transmission in Buenos Aires was modulated by temperature and triggered by imported cases coming from regions with ongoing outbreaks. However, local transmission was made possible and consolidated heterogeneously in the city due to housing and socioeconomic characteristics of the population, with 32.8% of autochthonous cases occurring in slums, which held only 6.4% of the city population. A hierarchical spatiotemporal model accounting for imperfect detection of cases showed that, outside slums, less-affluent neighborhoods of houses (vs. apartments) favored transmission. Global and local spatiotemporal point-pattern analyses demonstrated that most transmission occurred at or close to home. Additionally, based on these results, a point-pattern analysis was assessed for early identification of transmission foci during the outbreak while accounting for population spatial distribution. Altogether, our results reveal how social, physical, and biological processes shape dengue transmission in Buenos Aires and, likely, other non-endemic cities, and suggest multiple opportunities for control interventions.

Dengue fever is mainly transmitted by a mosquito species that is highly urbanized, and lays eggs and develops mostly in artificial water containers. Dengue transmission is sustained year-round in most tropical regions of the world, but in many subtropical/temperate regions it occurs only in the warmest months. To improve understanding of dengue transmission in these regions, we analyzed one of the largest outbreaks in Buenos Aires city, a subtropical metropolis. Based on information on 5,104 georeferenced cases during summer-autumn 2016, we found that most transmission occurred in or near home, that slums had the highest risk of transmission, and that, outside slums, less-affluent neighborhoods of houses (vs. apartments) favored transmission. We showed that the cumulative effects of temperature over the previous few weeks set the temporal limits for transmission to occur, and that the outbreak was sparked by infected people arriving from regions with ongoing outbreaks. Additionally, we implemented a statistical method to identify transmission foci in real-time that improves targeting control interventions. Our results deepen the understanding of dengue transmission as a result of social, physical, and biological processes, and pose multiple opportunities for improving control of dengue and other mosquito-borne viruses such as Zika, chikungunya, and yellow fever.

Differential inhibition of egg hatching in Aedes aegypti populations from localities with different winter conditions

In Argentina, the mosquito Aedes aegypti (L.) (Diptera: Culicidae) is distributed from subtropical to temperate climates. Here, we hypothesized that the expansion of Ae. aegypti into colder regions is favoured by high-phenotypic plasticity and an adaptive inhibition of egg hatching at low temperatures. Thus, we investigated the hatching response of eggs of three populations: one from a subtropical region (Resistencia) and two from temperate regions (Buenos Aires City and San Bernardo) of Argentina. Eggs collected in the field were raised in three experimental colonies. F1 eggs were acclimated for 7 days prior to immersion at 7.6 or 22°C (control eggs). Five immersion temperatures were tested: 7.6, 10.3, 11.8, 14.1 and 16°C (range of mean winter temperatures of the three localities). A second immersion at 22°C was performed 2 weeks later to assess the inhibition to hatch under favourable conditions. After the first immersion, we compared the proportions of hatched eggs and dead larvae among treatment levels, whereas after the second immersion we compared the hatching response among the three populations. The factors that most influenced the egg hatching response were the geographical origin of the populations and the immersion temperature, but not the acclimation temperature. The proportions of hatching and larval mortality at low temperatures were higher for Resistencia than for Buenos Aires and San Bernardo, whereas the hatching response at ambient temperature was lower for San Bernardo than for Buenos Aires and Resistencia. The results support the hypothesis that populations from colder regions show an adaptive inhibition of egg hatching.

Dynamic mapping of the probability of infestation by urban arbovirus vectors in the municipalities of Rio Grande do Sul state, Brazil, 2016-2017

OBJECTIVE

To compare official mapping with probabilistic mapping of infestation by Aedes spp. in the municipalities of Rio Grande do Sul state, Brazil.

METHODS

This was an ecological study using data from samples of mosquito breeding sites collected in 2016-2017; official classification was obtained from epidemiological reports, and infestation per municipality and week was estimated by fitting a dynamic site-occupancy model to data from municipal epidemiological surveillance.

RESULTS

187,245 samples collected in 473 municipalities returned 10,648 detections of Aedes aegypti, and 8,414 detections of Aedes albopictus; official mapping agrees with probabilistic mapping in municipalities in the northwestern and western regions of the state. The mappings are not in agreement in the eastern, central, northeastern and southern regions, revealing municipalities officially not infested but with high probability of infestation and notification of arbovirus infection.

CONCLUSION

While official classification identified critically infested municipalities in the state's northwestern and western regions, it did not identify infestation in municipalities with possible false zero errors and where infestation varies over time.

Increased size and energy reserves in diapausing eggs of temperate Aedes aegypti populations

Many insects overwinter in diapause, a pre-programmed anticipated response to unfavorable environmental conditions, often induced by a short-day photoperiod. Diapause involves morphological changes and increased energy stores required for metabolic demands during winter. In diapausing mosquito eggs, the accumulation of lipids plays an important role, because these molecules are the primary fuel consumed during embryogenesis and pharate larvae metabolism, and have a key role in egg desiccation resistance. The supposed inability of the mosquito Aedes aegypti to lay diapausing eggs has been recently challenged by a study on a temperate population, which showed that the inhibition of egg hatching in response to short days is possible in this species. Thus, the aim of the present study was to assess the effects of parental photoperiod on embryonic diapause-related traits, such as the triglyceride content and size of eggs laid, of two populations whose localities of origin differ in their winter length. Two colonies were maintained for each population: one under a Short-Day Photoperiod (SD: 10 h:14 h - Light:Dark) and the other under a Long-Day Photoperiod (LD: 14 h:10 h - Light:Dark). The eggs obtained from each combination of population and light treatment were used for size measurement (length, width and volume) and for the quantification of triglyceride content. Egg size showed differences between photoperiod treatments, with larger width and volume in eggs from the SD treatment. Remarkably, eggs from the SD treatment accumulated twice as many triglycerides as those from the LD treatment. Also, the eggs derived from the population having the longer winter accumulated larger amounts of triglycerides. The higher lipid content is probably contributing to a better survival during the cold season in both populations. The photoperiod-induced response in egg size and amount of triglycerides observed in this study support the hypothesis that the Ae. aegypti populations studied are able to lay diapausing eggs, a fact that provides physiological bases for the further expansion of this species to colder regions.

The Burden of Dengue in Children by Calculating Spatial Temperature: A Methodological Approach Using Remote Sensing Techniques

BACKGROUND

Dengue fever is one of the most important arboviral diseases. Surface temperature versus dengue burden in tropical environments can provide valuable information that can be adapted in future measurements to improve health policies.

METHODS

A methodological approach using Daymet-V3 provided estimates of daily weather parameters. A Python code developed by us extracted the median temperature from the urban regions of Colima State (207.3 km2) in Mexico. JointPoint regression models computed the mean temperature-adjusted average annual percentage of change (AAPC) in disability-adjusted life years (DALY) rates (per 100,000) due to dengue in Colima State among school-aged (5-14 years old) children.

RESULTS

Primary outcomes were average temperature in urban areas and cumulative dengue burden in DALYs in the school-aged population. A model from 1990 to 2017 medium surface temperature with DALY rates was performed. The increase in DALYs rate was 64% (95% CI, 44-87%), and it seemed to depend on the 2000-2009 estimates (AAPC = 185%, 95% CI 18-588).

CONCLUSION

From our knowledge, this is the first study to evaluate surface temperature and to model it through an extensive period with health economics calculations in a specific subset of the Latin-American endemic population for dengue epidemics.

Understanding the role of temporal variation of environmental variables in predicting Aedes aegypti oviposition activity in a temperate region of Argentina

Environmental variables related to vegetation and weather are some of the most influential factors that impacting Aedes (Stegomya) aegypti, a mosquito vector of dengue, chikungunya and Zika viruses. In this paper, we aim to develop temporal predictive models for Ae. aegypti oviposition activity utilizing vegetation and meteorological variables as predictors in Córdoba city (Argentina). Eggs were collected using ovitraps placed throughout the city from 2009 to 2012 that were replaced weekly. Temporal generalized linear mixed models were developed with negative binomial distributions of errors that model average number of eggs collected weekly as a function of vegetation and meteorological variables with time lags. The best model included a vegetation index, vapor pressure of water, precipitation and photoperiod. With each unit of increment in vegetation index per week the average number of eggs increased by 1.71 in the third week. Furthermore, each millimeter increase of accumulated rain during 4 weeks was associated with a decrease of 0.668 in the average number of eggs found in the following week. This negative effect of precipitation could occur during abundant rainfalls that fill containers completely, thereby depriving females of oviposition sites and leading them to search for other suitable breeding sites. Furthermore, the average number of eggs increased with the photoperiod at low values of mean vapor pressure; however the average number of eggs decreased at high values of mean vapor pressure, and the positive relationship between the response variable and mean vapor pressure was stronger at low values of photoperiod. Additionally, minimum temperature was associated positively with oviposition activity and that low minimum temperatures could be a limiting factor in Ae. aegypti oviposition activity. Our results emphasize the important role that climatic variables such as temperature, precipitation, and vapor pressure play in Ae. aegypti oviposition activity and how these variables along with vegetation indices can be used to inform predictive temporal models of Ae. aegypti population dynamics that can be used for informing mosquito population control and arbovirus mitigation strategies.

Exploring for Municipality-Level Socioeconomic Variables Related to Zika Virus Incidence in Colombia

Colombia experienced an outbreak of Zika virus infection during September 2015 until July 2016. This study aimed to identify the socioeconomic factors that at the municipality level correlate with this outbreak and therefore could have influenced its incidence. An analysis of publicly available, municipality-aggregated data related to eight potential explanatory socioeconomic variables was conducted. These variables are school dropout, low energy strata, social security system, savings capacity, tax, resources, investment, and debt. The response variable of interest in this study is the number of reported cases of Zika virus infection per people (projected) per square kilometer. Binomial regression models were performed. Results show that the best predictor variables of Zika virus occurrence, assuming an expected inverse relationship with socioeconomic status, are "school", "energy", and "savings". Contrary to expectations, proxies of socioeconomic status such as "investment", "tax", and "resources" were associated with an increase in the occurrence of Zika virus infection, while no association was detected for "social security" and "debt". Energy stratification, school dropout rate, and the percentage of the municipality's income that is saved conformed to the hypothesized inverse relationship between socioeconomic standing and Zika occurrence. As such, this study suggests these factors should be considered in Zika risk modeling.

Detection of Cell-Fusing Agent virus across ecologically diverse populations of Aedes aegypti on the Caribbean island of Saint Lucia

Background. Outbreaks of mosquito-borne arboviral diseases including dengue virus (DENV), Zika virus (ZIKV), yellow fever virus (YFV) and chikungunya virus (CHIKV) have recently occurred in the Caribbean. The geographical range of the principal vectors responsible for transmission, Aedes (Ae.) aegypti and Ae. albopictus are increasing and greater mosquito surveillance is needed in the Caribbean given international tourism is so prominent. The island of Saint Lucia has seen outbreaks of DENV and CHIKV in the past five years but vector surveillance has been limited with the last studies dating back to the late 1970s. Natural disasters have changed the landscape of Saint Lucia and the island has gone through significant urbanisation. Methods. In this study, we conducted an entomological survey of Ae. aegypti and Ae. albopictus distribution across the island and analysed environmental parameters associated with the presence of these species in addition to screening for medically important arboviruses and other flaviviruses. Results. Although we collected Ae. aegypti across a range of sites across the island, no Ae. albopictus were collected despite traps being placed in diverse ecological settings. The number of Ae. aegypti collected was significantly associated with higher elevation, and semi-urban settings yielded female mosquito counts per trap-day that were five-fold lower than urban settings. Screening for arboviruses revealed a high prevalence of cell-fusing agent virus (CFAV). Conclusions. Outbreaks of arboviruses transmitted by Ae. aegypti and Ae. albopictus have a history of occurring in small tropical islands and Saint Lucia is particularly vulnerable given the limited resources available to undertake vector control and manage outbreaks. Surveillance strategies can identify risk areas for predicting future outbreaks. Further research is needed to determine the diversity of current mosquito species, investigate insect-specific viruses, as well as pathogenic arboviruses, and this should also be extended to the neighbouring smaller Caribbean islands.

Predicting Aedes aegypti infestation using landscape and thermal features

Identifying Aedes aegypti breeding hotspots in urban areas is crucial for the design of effective vector control strategies. Remote sensing techniques offer valuable tools for mapping habitat suitability. In this study, we evaluated the association between urban landscape, thermal features, and mosquito infestations. Entomological surveys were conducted between 2016 and 2019 in Vila Toninho, a neighborhood of São José do Rio Preto, São Paulo, Brazil, in which the numbers of adult female Ae. aegypti were recorded monthly and grouped by season for three years. We used data from 2016 to 2018 to build the model and data from summer of 2019 to validate it. WorldView-3 satellite images were used to extract land cover classes, and land surface temperature data were obtained using the Landsat-8 Thermal Infrared Sensor (TIRS). A multilevel negative binomial model was fitted to the data, which showed that the winter season has the greatest influence on decreases in mosquito abundance. Green areas and pavements were negatively associated, and a higher cover of asbestos roofs and exposed soil was positively associated with the presence of adult females. These features are related to socio-economic factors but also provide favorable breeding conditions for mosquitos. The application of remote sensing technologies has significant potential for optimizing vector control strategies, future mosquito suppression, and outbreak prediction.

Delayed mortality effects of cold fronts during the winter season on Aedes aegypti in a temperate region

The expansion of the invasive mosquito Aedes aegypti L. (Diptera: Culicidae) towards temperate regions in the Americas is causing concern because of its public health implications. As for other insects, the distribution limits of Ae. aegypti have been suggested to be related to minimum temperatures and to be controlled mainly by cold tolerance. The aim of this study was to assess the daily mortality of immature stages of Ae. aegypti under natural winter conditions in Buenos Aires, Argentina, in relation to preceding thermal conditions. The experiment was performed outdoors, and one cohort of larvae was started each week for 16 weeks, and reared up to the emergence of the adults. Three times a week, larvae, pupae and emerged adults were counted, and these data were used to calculate the daily mortality of larvae, pupae and adults and to analyze their relationship with thermal conditions. The results showed that mortality was generally low, with a few peaks of high mortality after cold front events. The mortality of pupae and larvae showed a higher correlation with the cooling degree hours of previous days than with the minimum, maximum or mean temperatures. Pupae and adults showed to be more vulnerable to low temperatures than larvae. A delay in mortality was observed in relation to the low temperature events, with a proportion of individuals dying in a later stage after the end of the cold front. These results suggest that thermal conditions during cold fronts in Buenos Aires are close to the tolerance limit of the local Ae. aegypti population. The wide range of responses of different individuals suggests that low winter temperatures may constitute a selective force, leading the population to a higher tolerance to low temperatures, which might favor the further expansion of this species towards colder regions.

Simulation models of dengue transmission in Funchal, Madeira Island: Influence of seasonality

The recent emergence and established presence of Aedes aegypti in the Autonomous Region of Madeira, Portugal, was responsible for the first autochthonous outbreak of dengue in Europe. The island has not reported any dengue cases since the outbreak in 2012. However, there is a high risk that an introduction of the virus would result in another autochthonous outbreak given the presence of the vector and permissive environmental conditions. Understanding the dynamics of a potential epidemic is critical for targeted local control strategies. Here, we adopt a deterministic model for the transmission of dengue in Aedes aegypti mosquitoes. The model integrates empirical and mechanistic parameters for virus transmission, under seasonally varying temperatures for Funchal, Madeira Island. We examine the epidemic dynamics as triggered by the arrival date of an infectious individual; the influence of seasonal temperature mean and variation on the epidemic dynamics; and performed a sensitivity analysis on the following quantities of interest: the epidemic peak size, time to peak, and the final epidemic size. Our results demonstrate the potential for summer and autumn season transmission of dengue, with the arrival date significantly affecting the distribution of the timing and peak size of the epidemic. Late-summer arrivals were more likely to produce large epidemics within a short peak time. Epidemics within this favorable period had an average of 11% of the susceptible population infected at the peak, at an average peak time of 95 days. We also demonstrated that seasonal temperature variation dramatically affects the epidemic dynamics, with warmer starting temperatures producing large epidemics with a short peak time and vice versa. Overall, our quantities of interest were most sensitive to variance in the date of arrival, seasonal temperature, transmission rates, mortality rate, and the mosquito population; the magnitude of sensitivity differs across quantities. Our model could serve as a useful guide in the development of effective local control and mitigation strategies for dengue fever in Madeira Island.

Impacts of Low Temperatures on Wolbachia (Rickettsiales: Rickettsiaceae)-Infected Aedes aegypti (Diptera: Culicidae)

In recent decades, the occurrence and distribution of arboviral diseases transmitted by Aedes aegypti mosquitoes has increased. In a new control strategy, populations of mosquitoes infected with Wolbachia are being released to replace existing populations and suppress arboviral disease transmission. The success of this strategy can be affected by high temperature exposure, but the impact of low temperatures on Wolbachia-infected Ae. aegypti is unclear, even though low temperatures restrict the abundance and distribution of this species. In this study, we considered low temperature cycles relevant to the spring season that are close to the distribution limits of Ae. aegypti, and tested the effects of these temperature cycles on Ae. aegypti, Wolbachia strains wMel and wAlbB, and Wolbachia phage WO. Low temperatures influenced Ae. aegypti life-history traits, including pupation, adult eclosion, and fertility. The Wolbachia-infected mosquitoes, especially wAlbB, performed better than uninfected mosquitoes. Temperature shift experiments revealed that low temperature effects on life history and Wolbachia density depended on the life stage of exposure. Wolbachia density was suppressed at low temperatures but densities recovered with adult age. In wMel Wolbachia there were no low temperature effects specific to Wolbachia phage WO. The findings suggest that Wolbachia-infected Ae. aegypti are not adversely affected by low temperatures, indicating that the Wolbachia replacement strategy is suitable for areas experiencing cool temperatures seasonally.

Bio-eco-social determinants of Aedes breeding in field practice area of a medical college in Pune, Maharashtra

Background

Major determinant of dengue incidence is interaction between ecology, vector bionomics, and social factors.

Objectives

The objective of the study is to find out bio-eco-social determinants of Aedes breeding.

Methods

Background, household, entomological, and knowledge, attitude, and practice (KAP) surveys were undertaken post- and premonsoon showers from May to June 2016 in urban and rural practice area of medical college.

Results

A total of 181 and 204 households, 131 and 137 individuals, and 1250 and 1268 water-holding containers were included in household survey, KAP survey, and larval survey in urban slum and rural area, respectively. In both locations, maximum water-holding containers were indoors (41.4% and 61.8%, respectively); however, maximum positivity was peridomestic (63.6% and 83.1%, respectively). Pupae per container were 0.9 and 1.9 in respective locations and pupae per person were 1.2 and 2.3, respectively. Container positivity was seen in containers with rain as water source (8.8%) as well as among those who were never used (10.7%). Irregular water supply was significantly more in rural area (P < 0.05). KAP survey revealed that majority (90.1% and 71.5%, respectively) had heard about dengue, with significantly higher knowledge in urban slum, and television was the main source of information. Majority (89% and 83%, respectively) were unaware that peak biting time of Aedes is daytime. Use of mosquito repellent coils was the predominant preventive practice (46.6% and 61.2%, respectively). Pupae were reared; all were found to be Aedes aegypti.

Conclusions

Despite enhanced awareness campaigns, an integrated vector management approach is required for prevention of dengue.

Detection of a novel insect-specific flavivirus across ecologically diverse populations of Aedes aegypti on the Caribbean island of Saint Lucia

Background. Outbreaks of mosquito-borne arboviral diseases including dengue virus (DENV), Zika virus (ZIKV), yellow fever virus (YFV) and chikungunya virus (CHIKV) have recently occurred in the Caribbean. The geographical range of the principle vectors responsible for transmission, Aedes (Ae.) aegypti and Ae. albopictus is increasing and greater mosquito surveillance is needed in the Caribbean given international tourism is so prominent. The island of Saint Lucia has seen outbreaks of DENV and CHIKV in the past five years but vector surveillance has been limited with the last studies dating back to the late 1970s. Natural disasters have changed the landscape of Saint Lucia and the island has gone through significant urbanisation. Methods. In this study, we conducted an entomological survey of Ae. aegypti and Ae. albopictus distribution across the island and analysed environmental parameters associated with the presence of these species in addition to screening for medically important arboviruses and other flaviviruses. Results. Although we collected Ae. aegypti across a range of sites across the island, no Ae. albopictus were collected despite traps being placed in diverse ecological settings. The number of Ae. aegypti collected was significantly associated with higher elevation, and semi-urban settings yielded female mosquito counts per trap-day that were five-fold lower than urban settings. Screening for arboviruses revealed a high prevalence of a novel insect-specific flavivirus closely related to cell fusing agent virus (CFAV). Conclusions. Outbreaks of arboviruses transmitted by Ae. aegypti and Ae. albopictus have a history of occurring in small tropical islands and Saint Lucia is particularly vulnerable given the limited resources available to undertake vector control and manage outbreaks. Surveillance strategies can identify risk areas for predicting future outbreaks and further research is needed to determine the diversity of current mosquito species and this should be extended to the neighbouring smaller Caribbean islands.

Site Occupancy by Aedes aegypti in a Subtropical City is Most Sensitive to Control during Autumn and Winter Months

The Aedes aegypti mosquito inhabits most tropical and subtropical regions of the globe, where it transmits arboviral diseases of substantial public health relevance, such as dengue fever. In subtropical regions, Ae. aegypti often presents an annual abundance cycle driven by weather conditions. Because different population states may show varying responses to control, we are interested in studying what time of the year is most appropriate for control. To do so, we developed two dynamic site-occupancy models based on more than 200 weeks of mosquito trapping data from nearly 900 sites in a subtropical Brazilian city. Our phenomenological, Markovian models, fitted to data in a Bayesian framework, accounted for failure to detect mosquitoes in two alternative ways and for temporal variation in dynamic rates of local extinction and colonization of new sites. Infestation varied from nearly full cover of the city area in late summer, to between 10% and 67% of sites occupied in winter depending on the model. Sensitivity analysis reveals that changes in dynamic rates should have the greatest impact on site occupancy during autumn and early winter months, when the mosquito population is declining. We discuss the implications of this finding to the timing of mosquito control.

Modeling confinement and reversibility of threshold-dependent gene drive systems in spatially-explicit Aedes aegypti populations

Background

The discovery of CRISPR-based gene editing and its application to homing-based gene drive systems has been greeted with excitement, for its potential to control mosquito-borne diseases on a wide scale, and concern, for the invasiveness and potential irreversibility of a release. Gene drive systems that display threshold-dependent behavior could potentially be used during the trial phase of this technology, or when localized control is otherwise desired, as simple models predict them to spread into partially isolated populations in a confineable manner, and to be reversible through releases of wild-type organisms. Here, we model hypothetical releases of two recently engineered threshold-dependent gene drive systems—reciprocal chromosomal translocations and a form of toxin-antidote-based underdominance known as UD^MEL—to explore their ability to be confined and remediated.

Results

We simulate releases of Aedes aegypti, the mosquito vector of dengue, Zika, and other arboviruses, in Yorkeys Knob, a suburb of Cairns, Australia, where previous biological control interventions have been undertaken on this species. We monitor spread to the neighboring suburb of Trinity Park to assess confinement. Results suggest that translocations could be introduced on a suburban scale, and remediated through releases of non-disease-transmitting male mosquitoes with release sizes on the scale of what has been previously implemented. UD^MEL requires fewer releases to introduce, but more releases to remediate, including of females capable of disease transmission. Both systems are expected to be confineable to the release site; however, spillover of translocations into neighboring populations is less likely.

Conclusions

Our analysis supports the use of translocations as a threshold-dependent drive system capable of spreading disease-refractory genes into Ae. aegypti populations in a confineable and reversible manner. It also highlights increased release requirements when incorporating life history and population structure into models. As the technology nears implementation, further ecological work will be essential to enhance model predictions in preparation for field trials.

Accelerating invasion potential of disease vector Aedes aegypti under climate change

Vector-borne diseases remain a major contributor to the global burden of disease, while climate change is expected to exacerbate their risk. Characterising vector development rate and its spatio-temporal variation under climate change is central to assessing the changing basis of human disease risk. We develop a mechanistic phenology model and apply it to Aedes aegypti, an invasive mosquito vector for arboviruses (e.g. dengue, zika and yellow fever). The model predicts the number of life-cycle completions (LCC) for a given location per unit time based on empirically derived biophysical responses to environmental conditions. Results suggest that the world became ~1.5% more suitable per decade for the development of Ae. aegypti during 1950–2000, while this trend is predicted to accelerate to 3.2–4.4% per decade by 2050. Invasion fronts in North America and China are projected to accelerate from ~2 to 6 km/yr by 2050. An increase in peak LCC combined with extended periods suitable for mosquito development is simulated to accelerate the vector’s global invasion potential.

Understanding how life cycles of vectors respond to climatic factors is important to predict potential shifts in vector-borne disease risk in the coming decades. Here the authors develop a mechanistic phenological model for the invasive mosquito Aedes aegypti and apply it to project shifts under climate change scenarios.

The Influence of Meteorological Conditions on the Yellow Fever Epidemic in Cádiz (Southern Spain) in 1800: A Historical Scientific Controversy

A yellow fever epidemic occurred in Cádiz and other areas of southern Spain during the last months of 1800. An anonymous author attributed this disease to the contrast between the cold and rainy winter and spring, and the subsequent very hot summer. However, the physician J.M. Aréjula published a report in 1806 where he refuted this conclusion after a detailed analysis of the meteorological conditions in the area. This controversy is a good example of the discussion about the relationships between meteorological conditions and public health. In this work, this “scientific” controversy is studied. Although the arguments of both authors were inspired by the neo-Hippocratic medical paradigm, the anonymous author put forth a simple cause–effect hypothesis, while Aréjula recognized the complexity of the problem, introducing the concept of “concause” to explain the confluence of environmental and contagious effects.

Semi-field life-table studies of Aedes albopictus (Diptera: Culicidae) in Guangzhou, China

Background

Aedes albopictus is a major vector for several tropical infectious diseases. Characterization of Ae. albopictus development under natural conditions is crucial for monitoring vector population expansion, dengue virus transmission, and disease outbreak preparedness.

Methods

This study employed mosquito traits as a proxy to understanding life-table traits in mosquitoes using a semi–field study. Ae. albopictus larval and adult life-table experiments were conducted using microcosms under semi-field conditions in Guangzhou. Stage-specific development times and survivorship rates were determined and compared under semi-field conditions in different seasons from early summer (June) to winter (January), to determine the lower temperature limit for larval development and adult survivorship and reproductivity.

Results

The average egg- hatching rate was 60.1%, with the highest recorded in October (77.1%; mid-autumn). The larval development time was on average 13.2 days (range, 8.5–24.1 days), with the shortest time observed in September(8.7 days; early autumn) and longest in November (22.8 days). The pupation rates of Ae. albopictus larvae were on average 88.9% (range, 81.6–93.4%); they were stable from June to September but decreased from October to November. The adult emergence rates were on average 82.5% (range, 76.8–87.9%) and decreased from July to November. The median survival time of Ae. albopictus adults was on average 7.4 (range, 4.5–9.8), with the shortest time recorded in September. The average lifetime egg mass under semi-field conditions was 37.84 eggs/female. The larvae could develop into adults at temperatures as low as 12.3°C, and the adults could survive for 30.0 days at 16.3°C and still produce eggs. Overall, correlation analysis found that mean temperature and relative humidity were variables significantly affecting larval development and adult survivorship.

Conclusion

Ae. albopictus larvae could develop and emerge and the adults could survive and produce eggs in early winter in Guangzhou. The major impact of changes in ambient temperature, relative humidity, and light intensity was on the egg hatching rates, adult survival time, and egg mass production, rather than on pupation or adult emergence rates.

A Simple Model to Predict the Potential Abundance of Aedes aegypti Mosquitoes One Month in Advance

The mosquito Aedes (Stegomyia) aegypti (L.) is the primary vector of dengue, chikungunya, and Zika viruses in the United States. Surveillance for adult Ae. aegypti is limited, hindering understanding of the mosquito's seasonal patterns and predictions of areas at elevated risk for autochthonous virus transmission. We developed a simple, intuitive empirical model that uses readily available temperature and humidity variables to predict environmental suitability for low, medium, or high potential abundance of adult Ae. aegypti in a given city 1 month in advance. Potential abundance was correctly predicted in 73% of months in arid Phoenix, AZ (over a 10-year period), and 63% of months in humid Miami, FL (over a 2-year period). The monthly model predictions can be updated daily, weekly, or monthly and thus may be applied to forecast suitable conditions for Ae. aegypti to inform vector-control activities and guide household-level actions to reduce mosquito habitat and human exposure.