Mosquito infestation and dengue virus infection in Aedes aegypti females in schools in Merida, Mexico

Microclimate factors related to dengue virus burden clusters in two endemic towns of Mexico

In dengue-endemic areas, transmission control is limited by the difficulty of achieving sufficient coverage and sustainability of interventions. To maximize the effectiveness of interventions, areas with higher transmission could be identified and prioritized. The aim was to identify burden clusters of Dengue virus (DENV) infection and evaluate their association with microclimatic factors in two endemic towns from southern Mexico. Information from a prospective population cohort study (2·5 years of follow-up) was used, microclimatic variables were calculated from satellite information, and a cross-sectional design was conducted to evaluate the relationship between the outcome and microclimatic variables in the five surveys. Spatial clustering was observed in specific geographic areas at different periods. Both, land surface temperature (aPR 0·945; IC95% 0·895-0·996) and soil humidity (aPR 3·018; IC95% 1·013-8·994), were independently associated with DENV burden clusters. These findings can help health authorities design focused dengue surveillance and control activities in dengue endemic areas.

Indian Ocean temperature anomalies predict long-term global dengue trends

Despite identifying El Niño events as a factor in dengue dynamics, predicting the oscillation of global dengue epidemics remains challenging. Here, we investigate climate indicators and worldwide dengue incidence from 1990 to 2019 using climate-driven mechanistic models. We identify a distinct indicator, the Indian Ocean basin-wide (IOBW) index, as representing the regional average of sea surface temperature anomalies in the tropical Indian Ocean. IOBW is closely associated with dengue epidemics for both the Northern and Southern hemispheres. The ability of IOBW to predict dengue incidence likely arises as a result of its effect on local temperature anomalies through teleconnections. These findings indicate that the IOBW index can potentially enhance the lead time for dengue forecasts, leading to better-planned and more impactful outbreak responses.

Spatial analysis of dengue transmission in an endemic city in Brazil reveals high spatial structuring on local dengue transmission dynamics

In the last decades, dengue has become one of the most widespread mosquito-borne arboviruses in the world, with an increasing incidence in tropical and temperate regions. The mosquito Aedes aegypti is the dengue primary vector and is more abundant in highly urbanized areas. Traditional vector control methods have showing limited efficacy in sustaining mosquito population at low levels to prevent dengue virus outbreaks. Considering disease transmission is not evenly distributed in the territory, one perspective to enhance vector control efficacy relies on identifying the areas that concentrate arbovirus transmission within an endemic city, i.e., the hotspots. Herein, we used a 13-month timescale during the SARS-Cov-2 pandemic and its forced reduction in human mobility and social isolation to investigate the spatiotemporal association between dengue transmission in children and entomological indexes based on adult Ae. aegypti trapping. Dengue cases and the indexes Trap Positive Index (TPI) and Adult Density Index (ADI) varied seasonally, as expected: more than 51% of cases were notified on the first 2 months of the study, and higher infestation was observed in warmer months. The Moran's Eigenvector Maps (MEM) and Generalized Linear Models (GLM) revealed a strong large-scale spatial structuring in the positive dengue cases, with an unexpected negative correlation between dengue transmission and ADI. Overall, the global model and the purely spatial model presented a better fit to data. Our results show high spatial structure and low correlation between entomological and epidemiological data in Foz do Iguaçu dengue transmission dynamics, suggesting the role of human mobility might be overestimated and that other factors not evaluated herein could be playing a significant role in governing dengue transmission.

West Nile virus in Mexico: Why vectors matter for explaining the current absence of epidemics

Since 2002, West Nile Virus (WNV) has been reported in 18 states in Mexico, either by PCR or serological testing. However, it is believed that the virus is present in more states. Only four states (out of 32) have reported confirmed human cases, and one state has serological evidence. In the country, WNV is present in mainly horses and birds, but its presence extends to crocodiles, felines, canines, swines, donkeys, caprines, antilopes, cattle, bats, and camelids. Positive mosquito species include Aedes and Culex spp. Different hypotheses have been proposed to explain the absence of WNV epidemics in Latin America. Since some regions of Mexico and the United States share ecological and climatic conditions, these hypotheses may not be sufficient to account for the absence of WNV outbreaks or epidemics. This paper discusses the proposed ideas and attempts to contextualize them for Mexico, particularly for the U.S.-Mexico border, where WNV infections have been reported in humans, horses, and mosquitoes. We propose that integration of urban ecology and entomology knowledge is needed to better understand the absence of WN cases in Mexico.

School and community driven dengue vector control and monitoring in Myanmar: Study protocol for a cluster randomized controlled trial

Background

Dengue is the most common and widespread mosquito-borne arboviral disease globally estimated to cause >390 million infections and >20,000 deaths annually. There are no effective preventive drugs and the newly introduced vaccines are not yet available. Control of dengue transmission still relies primarily on mosquito vector control. Although most vector control methods currently used by national dengue control programs may temporarily reduce mosquito populations, there is little evidence that they affect transmission. There is an urgent need for innovative, participatory, effective, and locally adapted approaches for sustainable vector control and monitoring in which students can be particularly relevant contributors and to demonstrate a clear link between vector reduction and dengue transmission reduction, using tools that are inexpensive and easy to use by local communities in a sustainable manner.

Methods

Here we describe a cluster randomized controlled trial to be conducted in 46 school catchment areas in two townships in Yangon, Myanmar. The outcome measures are dengue cases confirmed by rapid diagnostic test in the townships, dengue incidence in schools, entomological indices, knowledge, attitudes and practice, behavior, and engagement.

Conclusions

The trial involves middle school students that positions them to become actors in dengue knowledge transfer to their communities and take a leadership role in the delivery of vector control interventions and monitoring methods. Following this rationale, we believe that students can become change agents of decentralized vector surveillance and sustainable disease control in line with recent new paradigms in integrated and participatory vector surveillance and control. This provides an opportunity to operationalize transdisciplinary research towards sustainable health development. Due to the COVID-19 pandemic and political instability in Myanmar the project has been terminated by the donor, but the protocol will be helpful for potential future implementation of the project in Myanmar and/or elsewhere.Registration: This trial was registered in the ISRCTN Registry on 31 May 2022 ( https://doi.org/10.1186/ISRCTN78254298).

Is the presence of mosquitoes an indicator of poor environmental sanitation?

The World Health Organization has designated mosquitoes as the most lethal animal since they are known to spread pathogen-transmitting organisms. Understanding the many environmental elements that contribute to the spread of these vectors is one of the many strategies used to stop them. If there are mosquitoes around people, it may indicate that there is not an appropriate environmental sanitation program in place in the community or region. Environmental sanitation involves improving any elements of the physical environment that could have a negative impact on a person's survival, health, or physical environment. Keywords containing 'Aedes,' 'Culex,' 'Anopheles,' 'dengue,' 'malaria,' 'yellow fever,' 'Zika,' 'West Nile,' 'chikungunya,' 'resident,' 'environment,' 'sanitation,' 'mosquito control,' and 'breeding sites' of published articles on PubMed, Google Scholar, and ResearchGate were reviewed. It was discovered that the general population should be involved in mosquito and mosquito-borne disease control. Collaboration between health professionals and the general population is essential. The purpose of this paper is to increase public awareness of environmental health issues related to diseases carried by mosquitoes.

School and community driven dengue vector control and monitoring in Myanmar: Study protocol for a cluster randomized controlled trial

Background. Dengue is the most common and widespread mosquito-borne arboviral disease globally estimated to cause >390 million infections and >20,000 deaths annually. There are no effective vaccines or preventive drugs. Control of dengue transmission relies primarily on mosquito vector control. Although most vector control methods currently used by national dengue control programs may temporarily reduce mosquito populations, there is little evidence that they affect transmission. There is an urgent need for innovative, participatory, effective, and locally adapted approaches for sustainable vector control and monitoring in which students can be particularly relevant contributors and to demonstrate a clear link between vector reduction and dengue transmission reduction, using tools that are inexpensive and easy to use by local communities in a sustainable manner. Methods. Here we describe a cluster randomized controlled trial to be conducted in 46 school catchment areas in two townships in Yangon, Myanmar. The outcome measures are dengue cases confirmed by rapid diagnostic test in the townships, dengue incidence in schools, entomological indices, knowledge, attitudes and practice, behavior, and engagement. Conclusions. The trial involves middle school students that positions them to become actors in dengue knowledge transfer to their communities and take a leadership role in the delivery of vector control interventions and monitoring methods. Following this rationale, we believe that students can become change agents of decentralized vector surveillance and sustainable disease control in line with recent new paradigms in integrated and participatory vector surveillance and control. This provides an opportunity to operationalize transdisciplinary research towards sustainable health development. Due to the COVID-19 pandemic and political instability in Myanmar the project has been terminated by the donor, but the protocol will be helpful for potential future implementation of the project in Myanmar and/or elsewhere. Registration: This trial was registered in the ISRCTN Registry on 31 May 2022 (https://doi.org/10.1186/ISRCTN78254298).

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.

Surveillance of dengue virus in individual Aedes aegypti mosquitoes collected concurrently with suspected human cases in Tarlac City, Philippines

BACKGROUND

Vector control measures are critical for the prevention and reduction of dengue virus (DENV) transmission. Effective vector control is reliant not only on knowledge of mosquito abundance, but also on the timely and accurate detection of mosquito-borne infection. Mosquito-based virus surveillance programs typically rely on pool-based mosquito testing, although whether individual-based mosquito testing is a feasible alternative to this has not been widely studied. Applying an individual-based mosquito testing approach, we conducted a 1-month surveillance study of DENV in adult Aedes aegypti mosquitoes in homes of suspected dengue patients during the 2015 peak dengue season in Tarlac City, Philippines to more accurately assess the mosquito infection rate and identify the DENV serotypes and genotypes concurrently co-circulating in mosquitoes and patients there.

METHODS

We performed a one-step multiplex real-time reverse transcription-polymerase chain reaction (RT-PCR) assay for the simultaneous detection and serotyping of DENV in patients and individual female Ae. aegypti mosquitoes. Additionally, we performed sequencing and phylogenetic analyses to further characterize the detected DENV serotypes in mosquitoes and patients at the genotype level.

RESULTS

We collected a total of 583 adult Ae. aegypti mosquitoes, of which we individually tested 359 female mosquitoes for the presence of DENV. Ten (2.8%) of the 359 female mosquitoes were positive for the presence of DENV. We detected DENV-1, DENV-2, and DENV-4 in the field-collected mosquitoes, which was consistent with the serotypes concurrently found in infected patients. Sequencing and phylogenetic analyses of the detected DENV serotypes based on the partial sequence of the evelope (E) gene revealed three genotypes concurrently present in the sampled mosquitoes and patients during the study period, namely DENV-1 genotype IV, DENV-2 Cosmopolitan genotype, and DENV-4 genotype II.

CONCLUSIONS

We demonstrated the utility of a one-step multiplex real-time RT-PCR assay for the individual-based DENV surveillance of mosquitoes. Our findings reinforce the importance of detecting and monitoring virus activity in local mosquito populations, which are critical for dengue prevention and control.

Entomological and virological surveillance for dengue virus in churches in Merida, Mexico

This study was designed to assess whether churches in endemic dengue districts in Merida, Mexico provide suitable breeding habitats for mosquitoes and are potential sites for dengue virus (DENV) transmission. Churches were inspected for immature and adult mosquitoes once every week from November 2015 to October 2016. A total of 10,997 immatures of five species were collected. The most abundant species were Aedes aegypti (6,051) and Culex quinquefasciatus (3,018). The most common source of immature Ae. aegypti were buckets followed by disposable containers. Adult collections yielded 21,226 mosquitoes of nine species. The most common species were Cx. quinquefasciatus (15,215) and Ae. aegypti (3,902). Aedes aegypti were found all year long. Female Ae. aegypti (1,380) were sorted into pools (166) and assayed for flavivirus RNA by RT-PCR and Sanger sequencing. Two pools were positive for DENV (DENV-1 and 2). In conclusion, we demonstrated that some churches in Merida are infested with mosquitoes all year long and they potentially serve as sites for DENV transmission and should therefore be considered for inclusion in mosquito and arboviruses control and surveillance efforts.

Epidemiological characteristics and determinants of dengue transmission during epidemic and non-epidemic years in Fortaleza, Brazil: 2011-2015

BACKGROUND

After being eliminated during the 1950s, dengue reemerged in Brazil in the 1980s. Since then, incidence of the disease has increased, as serotypes move within and between cities. The co-circulation of multiple serotypes contributes to cycles of epidemic and interepidemic years, and a seasonal pattern of transmission is observed annually. Little is known regarding possible differences in the epidemiology of dengue under epidemic and interepidemic scenarios. This study addresses this gap and aims to assess the epidemiological characteristics and determinants of epidemic and interepidemic dengue transmission, utilizing data from the 5th largest city in Brazil (Fortaleza), at fine spatial and temporal scales.

METHODS/PRINCIPAL FINDINGS

Longitudinal models of monthly rates of confirmed dengue cases were used to estimate the differential contribution of contextual factors to dengue transmission in Fortaleza between 2011 and 2015. Models were stratified by annual climatological schedules and periods of interepidemic and epidemic transmission, controlling for social, economic, structural, entomological, and environmental factors. Results revealed distinct seasonal patterns between interepidemic and epidemic years, with persistent transmission after June in interepidemic years. Dengue was strongly associated with violence across strata, and with poverty and irregular garbage collection during periods of low transmission, but not with other indicators of public service provision or structural deprivation. Scrapyards and sites associated with tire storage were linked to incidence differentially between seasons, with the strongest associations during transitional precipitation periods. Hierarchical clustering analysis suggests that the dengue burden concentrates in the southern periphery of the city, particularly during periods of minimal transmission.

CONCLUSIONS/SIGNIFICANCE

Our findings have direct programmatic implications. Vector control operations must be sustained after June even in non-epidemic years. More specifically, scrapyards and sites associated with tires (strongly associated with incidence during periods of minimal transmission), require sustained entomological surveillance, particularly during interepidemic intervals and in the urban periphery. Intersectoral collaborations that address urban violence are critical for facilitating the regular activities of vector control agents.

Study of Aedes aegypti population with emphasis on the gonotrophic cycle length and identification of arboviruses: implications for vector management in cemeteries

Aedes aegypti is the vector of the arboviruses causing dengue, chikungunya and zika infections in Mexico. However, its presence in public places has not been fully evaluated. In a cemetery from Merida, Yucatan, Mexico, the productivity of Ae. aegypti, the gonotrophic cycle, and the presence of Ae. aegypti females infected with arboviruses were evaluated. Immature and adult mosquitoes were inspected every two months between April 2016 to June 2017. For the gonotrophic cycle length, the daily pattern of total and parous female ratio was registered and was analyzed using time series analysis. Ae. aegypti females were sorted into pools and assayed for flavivirus RNA by RT-PCR and Sanger sequencing. Aedes aegypti immatures represented 82.86% (8,627/10,411) of the collection. In total, 1,648 Ae. aegypti females were sorted into 166 pools. Two pools were positive; one for dengue virus (DENV-1) and the other for zika virus (ZIKV). The phylogenetic analysis revealed that the DENV-1 is more closely related to isolates from Brazil. While ZIKV is more closely related to the Asian lineage, which were isolates from Guatemala and Mexico. We report some evidence of vertical transmission of DENV-1 in nulliparous females of Ae. aegypti. The gonotrophic cycle was four and three days in the rainy and dry season, respectively. The cemetery of Merida is an important focus of Ae. aegypti proliferation, and these environments may play a role in arboviruses transmission; probably limiting the efficacy of attempts to suppress the presence of mosquitoes in domestic environments.

The Use of Insecticide-Treated Curtains for Control of Aedes aegypti and Dengue Virus Transmission in "Fraccionamiento" Style Houses in México

Dengue, chikungunya, yellow fever, and Zika viruses transmitted by Aedes aegypti mosquitoes are major public health threats in the tropical and subtropical world. In México, construction of large tracts of “fraccionamientos” high density housing to accommodate population growth and urbanization has provided fertile ground for Ae. aegypti-transmitted viruses. We investigated the utility of pyrethroid-treated window curtains to reduce both the abundance of Ae. aegypti and to prevent dengue virus (DENV) transmission in fraccionamiento housing. Windows and doors of fraccionamiento homes in urban/suburban areas, where Ae. aegypti pyrethroid resistance associated with the Ile1016 knock down resistance (kdr) mutation in the voltage gated sodium channel gene was high, and in rural areas, where kdr resistance was low, were fitted with either insecticide-treated curtains (ITCs) or non-treated curtains (NTCs). The homes were monitored for mosquito abundance and DENV infection. ITCs reduced the indoor abundance of Ae. aegypti and the number of DENV-infected mosquitoes in homes in rural but not in urban/suburban study sites. The presence of non-treated screens also was associated with reduced numbers of mosquitoes in homes. “Super-infested” homes, yielding more than 50 mosquitoes, including DENV-infected mosquitoes, provide a significant public health risk to occupants, visitors, and people in neighboring homes.

Effectiveness of a novel long-lasting pyriproxyfen larvicide (SumiLarv®2MR) against Aedes mosquitoes in schools in Yangon, Myanmar

Background

Mosquito-borne diseases are prevalent in Myanmar, with the number of dengue cases showing a significant increase in recent years. Dengue vectors have developed resistance to insecticides and currently used larvicides show only short-term effectiveness. As a result, an alternative larvicide is urgently needed. The present study evaluated the larvicidal effectiveness of long-lasting pyriproxyfen resin discs (SumiLarv®2MR) against dengue virus vectors in schools in Hlaing Thar Yar Township, Yangon.

Results

The proportion of Aedes mosquito-infested containers was significantly reduced in the schools applied with the larvicide (OR: 0.24, 95% CI: 0.12–0.48) while there was little reduction noted in the control schools (OR: 0.97, 95% CI: 0.55–1.72). The density of infested containers was also significantly reduced in the intervention schools (Beta: -1.50, 95% CI: -1.98– -1.04), but there was no significant reduction in density in the control schools (Beta: -0.19, 95% CI: -0.53–0.14). The proportion of adult emergence was less than 20% in the treated water collected from the intervention schools for six months, while the proportion was over 90% in the untreated water. In addition, eight-month-old SumiLarv®2MR resin discs were still 100% effective when tested in the laboratory. More than 50% of the discs disappeared from treated containers within two months of intervention.

Conclusions

SumiLarv®2MR was effective in reducing Aedes-infested containers at least six months after its application in schools. This new pyriproxyfen formulation has great potential for improving the current dengue vector control program in Myanmar.

Application of Artificial Neural Networks for Dengue Fever Outbreak Predictions in the Northwest Coast of Yucatan, Mexico and San Juan, Puerto Rico

Modelling dengue fever in endemic areas is important to mitigate and improve vector-borne disease control to reduce outbreaks. This study applied artificial neural networks (ANNs) to predict dengue fever outbreak occurrences in San Juan, Puerto Rico (USA), and in several coastal municipalities of the state of Yucatan, Mexico, based on specific thresholds. The models were trained with 19 years of dengue fever data for Puerto Rico and six years for Mexico. Environmental and demographic data included in the predictive models were sea surface temperature (SST), precipitation, air temperature (i.e., minimum, maximum, and average), humidity, previous dengue cases, and population size. Two models were applied for each study area. One predicted dengue incidence rates based on population at risk (i.e., numbers of people younger than 24 years), and the other on the size of the vulnerable population (i.e., number of people younger than five years and older than 65 years). The predictive power was above 70% for all four model runs. The ANNs were able to successfully model dengue fever outbreak occurrences in both study areas. The variables with the most influence on predicting dengue fever outbreak occurrences for San Juan, Puerto Rico, included population size, previous dengue cases, maximum air temperature, and date. In Yucatan, Mexico, the most important variables were population size, previous dengue cases, minimum air temperature, and date. These models have predictive skills and should help dengue fever mitigation and management to aid specific population segments in the Caribbean region and around the Gulf of Mexico.

Patterns of Urban Housing Shape Dengue Distribution in Singapore at Neighborhood and Country Scales

Dengue is the most important human arboviral disease in Singapore. We classified residential areas into low-rise and high-rise housing and investigated the influence of urban drainage on the distribution of dengue incidence and outdoor breeding at neighborhood and country scales. In Geylang area (August 2014 to August 2015), dengue incidence was higher in a subarea of low-rise housing compared to high-rise one, averaging 26.7 (standard error, SE = 4.83) versus 2.43 (SE = 0.67) per 1,000 people. Outdoor breeding drains of Aedes aegypti have clustered in the low-rise housing subarea. The pupal density per population was higher in the low-rise blocks versus high-rise ones, 246 (SE = 69.08) and 35.4 (SE = 25.49) per 1,000 people, respectively. The density of urban drainage network in the low-rise blocks is double that in the high-rise ones, averaging 0.05 (SE = 0.0032) versus 0.025 (SE = 0.00245) per meter. Further, a holistic analysis at a country-scale has confirmed the role of urban hydrology in shaping dengue distribution in Singapore. Dengue incidence (2013-2015) is proportional to the fractions of the area (or population) of low-rise housing. The drainage density in low-rise housing is 4 times that corresponding estimate in high-rise areas, 2.59 and 0.68 per meter, respectively. Public housing in agglomerations of high-rise buildings could have a positive impact on dengue if this urban planning comes at the expense of low-rise housing. City planners in endemic regions should consider the density of drainage networks for both the prevention of flooding and the breeding of mosquitoes.

Blood Feeding Status, Gonotrophic Cycle and Survivorship of Aedes (Stegomyia) aegypti (L.) (Diptera: Culicidae) Caught in Churches from Merida, Yucatan, Mexico

Blood-feeding status, gonotrophic cycle, and survival rates of Aedes (Stegmyia) aegypti (L.) was investigated in catholic churches from Merida, Yucatan. Female Ae. aegypti were caught using backpack aspirator during 25 consecutive days in rainy (2015) and dry season (2016). Blood-feeding status was determined by external examination of the abdomen and classified as unfed, fed, and gravid. Daily changes in the parous-nulliparous ratio were recorded, and the gonotrophic cycle length was estimated by a time series analysis. Also, was observed the vitellogenesis to monitoring egg maturity. In total, 408 females Ae. aegypti were caught, and there was a significant difference in the number of females collected per season (Z = -6.729, P ≤ 0.05). A great number was caught in the rainy season (n = 329). In the dry season, 79 females were caught, which the fed females were twice greatest than the unfed. The length of gonotrophic cycle was estimated on the base of a high correlation coefficient value appearing every 4 days in rainy at 26.7 ± 1.22°C, and 3 days in dry season at 29.8 ± 1.47°C. The daily survival rate of the Ae. aegypti population was higher in both seasons, 0.94 and 0.93 for the rainy and dry season, respectively. The minimum time estimated for developing mature eggs after blood feeding was similar in both seasons (3.5 days in rainy versus 3.25 days in dry). The measurement of the vectorial capacity of Ae. aegypti in catholic churches could help to understand the dynamics of transmission of arboviruses in sites with high human aggregation.

The importance of human population characteristics in modeling Aedes aegypti distributions and assessing risk of mosquito-borne infectious diseases

Background

The mosquito Aedes aegypti has long been a vector for human illness in the Southeastern United States. In the past, it has been responsible for outbreaks of dengue, chikungunya, and yellow fever and, very recently, the Zika virus that has been introduced to the region. Multiple studies have modeled the geographic distribution of Ae. aegypti as a function of climate factors; however, this ignores the importance of humans to the anthropophilic biter. Furthermore, Ae. aegypti thrives in areas where humans have created standing water sites, such as water storage containers and trash. As models are developed to examine the potential impact of climate change, it becomes increasingly important to include the most comprehensive set of predictors possible.

Results

This study uses Maxent, a species distribution model, to evaluate the effects of adding poverty and population density to climate-only models. Performance was evaluated through model fit statistics, such as AUC, omission, and commission, as well as individual variable contributions and response curves. Models which included both population density and poverty exhibited better predictive power and produced more precise distribution maps. Furthermore, the two human population characteristics accounted for much of the model contribution-more so than climate variables.

Conclusions

Modeling mosquito distributions without accounting for their dependence on local human populations may miss factors that are very important to niche realization and subsequent risk of infection for humans. Further research is needed to determine if additional human characteristics should be evaluated for model inclusion.

Modelling dengue fever risk in the State of Yucatan, Mexico using regional-scale satellite-derived sea surface temperature

Accurately predicting vector-borne diseases, such as dengue fever, is essential for communities worldwide. Changes in environmental parameters such as precipitation, air temperature, and humidity are known to influence dengue fever dynamics. Furthermore, previous studies have shown how oceanographic variables, such as El Niño Southern Oscillation (ENSO)-related sea surface temperature from the Pacific Ocean, influences dengue fever in the Americas. However, literature is lacking on the use of regional-scale satellite-derived sea surface temperature (SST) to assess its relationship with dengue fever in coastal areas. Data on confirmed dengue cases, demographics, precipitation, and air temperature were collected. Incidence of weekly dengue cases was examined. Stepwise multiple regression analyses (AIC model selection) were used to assess which environmental variables best explained increased dengue incidence rates. SST, minimum air temperature, precipitation, and humidity substantially explained 42% of the observed variation (r²=0.42). Infectious diseases are characterized by the influence of past cases on current cases and results show that previous dengue cases alone explained 89% of the variation. Ordinary least-squares analyses showed a positive trend of 0.20±0.03°C in SST from 2006 to 2015. An important element of this study is to help develop strategic recommendations for public health officials in Mexico by providing a simple early warning capability for dengue incidence.

Mosquito-borne and sexual transmission of Zika virus: Recent developments and future directions

Zika virus (ZIKV; Genus Flavivirus, Family Flaviviridae) has recently emerged in Asia and the Americas to cause large outbreaks of human disease. The outbreak has been characterized by high attack rates, birth defects in infants and severe neurological complications in adults. ZIKV is transmitted to humans by Aedes mosquitoes, but recent evidence implicates sexual transmission as playing an important role as well. This review highlights the transmission of ZIKV in humans, with a focus on both mosquito and sexually-transmitted routes and their outcomes. We also discuss critical directions for future research.

Mosquitoes on a plane: Disinsection will not stop the spread of vector-borne pathogens, a simulation study

Mosquito-borne diseases are increasingly being recognized as global threats, with increased air travel accelerating their occurrence in travelers and their spread to new locations. Since the early days of aviation, concern over the possible transportation of infected mosquitoes has led to recommendations to disinsect aircraft. Despite rare reports of mosquitoes, most likely transported on aircraft, infecting people far from endemics areas, it is unclear how important the role of incidentally transported mosquitoes is compared to the role of traveling humans. We used data for Plasmodium falciparum and dengue viruses to estimate the probability of introduction of these pathogens by mosquitoes and by humans via aircraft under ideal conditions. The probability of introduction of either pathogen by mosquitoes is low due to few mosquitoes being found on aircraft, low infection prevalence among mosquitoes, and high mortality. Even without disinsection, introduction via infected human travelers was far more likely than introduction by infected mosquitoes; more than 1000 times more likely for P. falciparum and more than 200 times more likely for dengue viruses. Even in the absence of disinsection and under the most favorable conditions, introduction of mosquito-borne pathogens via air travel is far more likely to occur as a result of an infected human travelling rather than the incidental transportation of infected mosquitoes. Thus, while disinsection may serve a role in preventing the spread of vector species and other invasive insects, it is unlikely to impact the spread of mosquito-borne pathogens.

Ecological Niche Model for Predicting Distribution of Disease-Vector Mosquitoes in Yucatán State, México

The majority of the Yucatán State, México, presents subtropical climate that is suitable for many species of mosquitoes that are known to be vectors of diseases, including those from the genera Aedes and Culex. The objective of this study is to identify the geographic distribution of five species from these two genera and estimate the human population at risk of coming in contact with them. We compiled distributional data for Aedes aegypti (L.), Aedes (Howardina) cozumelensis (Diaz Najera), Culex coronator Dyar and Knab, Culex quinquefasciatus Say, and Culex thriambus Dyar from several entomological studies in Yucatán between March 2010 and September 2014. Based on these data, we constructed ecological niche models to predict the spatial distribution of each species using the MaxEnt algorithm. Our models identified areas with suitable environments for Ae. aegypti in most of Yucatán. A similar percentage of urban (97.1%) and rural (96.5%) populations were contained in areas of highest suitability for Ae. aegypti, and no spatial pattern was found (Moran's I = 0.33, P = 0.38); however, we found an association of abundance of immature forms of this species with annual mean temperature (r = 0.19, P ≤ 0.001) and annual precipitation (r = 0.21, P ≤ 0.001). Aedes cozumelensis is also distributed in most areas of the Yucatán State; Cx. quinquefasciatus, Cx. coronator, and Cx. thriambus are restricted to the northwest. The information generated in this study can inform decision-making to address control measures in priority areas with presence of these vectors.

School-Based Health Education in Yucatan, Mexico about the Chikungunya Virus and Mosquito Illness Prevention

The Chikungunya virus (CHIKV) has been rapidly spreading throughout Latin America, utilizing pre-existing vectors to infiltrate the immunologically naïve populations. With the current rise of the Zika Virus, there is an urgent need for more rigorous vector control efforts to prevent further Zika breakout. We designed a school-based education module on CHIKV and mosquito prevention and presented it to the local students of ages of 6-18 in a rural town called Sudzal in Yucatan, Mexico. We distributed questionnaires before and after education to test the students’ knowledge of CHIKV and mosquito prevention. Chi-squared test was performed to determine the efficacy of the presentation in increasing their knowledge. The education presentation has proven to effectively educate the local residents in several critical methods of mosquito prevention, increasing the average test scores by 67% post-education. These include applying repellent, staying hydrated during recuperation, and cleaning indoor water containers to eliminate breeding sites (P<0.001). Furthermore, the questionnaire captured the residents’ behavioral patterns regarding CHIKV and mosquito prevention and identified cultural, ecological, and socioeconomic factors hindering effective implementation of vector control.

A Cluster-Randomized Controlled Trial to Reduce Diarrheal Disease and Dengue Entomological Risk Factors in Rural Primary Schools in Colombia

BACKGROUND

As many neglected tropical diseases are co-endemic and have common risk factors, integrated control can efficiently reduce disease burden and relieve resource-strained public health budgets. Diarrheal diseases and dengue fever are major global health problems sharing common risk factors in water storage containers. Where provision of clean water is inadequate, water storage is crucial. Fecal contamination of stored water is a common source of diarrheal illness, but stored water also provides breeding sites for dengue vector mosquitoes. Integrating improved water management and educational strategies for both diseases in the school environment can potentially improve the health situation for students and the larger community. The objective of this trial was to investigate whether interventions targeting diarrhea and dengue risk factors would significantly reduce absence due to diarrheal disease and dengue entomological risk factors in schools.

METHODOLOGY/PRINCIPAL FINDINGS

A factorial cluster randomized controlled trial was carried out in 34 rural primary schools (1,301 pupils) in La Mesa and Anapoima municipalities, Cundinamarca, Colombia. Schools were randomized to one of four study arms: diarrhea interventions (DIA), dengue interventions (DEN), combined diarrhea and dengue interventions (DIADEN), and control (CON). Interventions had no apparent effect on pupil school absence due to diarrheal disease (p = 0.45) or on adult female Aedes aegypti density (p = 0.32) (primary outcomes). However, the dengue interventions reduced the Breteau Index on average by 78% (p = 0.029), with Breteau indices of 10.8 and 6.2 in the DEN and DIADEN arms, respectively compared to 37.5 and 46.9 in the DIA and CON arms, respectively. The diarrhea interventions improved water quality as assessed by the amount of Escherichia coli colony forming units (CFU); the ratio of Williams mean E. coli CFU being 0.22, or 78% reduction (p = 0.008).

CONCLUSIONS/SIGNIFICANCE

Integrated control of dengue and diarrhea has never been conducted before. This trial presents an example for application of control strategies that may affect both diseases and the first study to apply such an approach in school settings. The interventions were well received and highly appreciated by students and teachers. An apparent absence of effect in primary outcome indicators could be the result of pupils being exposed to risk factors outside the school area and mosquitoes flying in from nearby uncontrolled breeding sites. Integrated interventions targeting these diseases in a school context remain promising because of the reduced mosquito breeding and improved water quality, as well as educational benefits. However, to improve outcomes in future integrated approaches, simultaneous interventions in communities, in addition to schools, should be considered; using appropriate combinations of site-specific, effective, acceptable, and affordable interventions.

TRIAL REGISTRATION

ClinicalTrials.gov no. ISRCTN40195031.

Spatial Variations in Dengue Transmission in Schools in Thailand

Background

Dengue is an important neglected tropical disease, with more than half of the world’s population living in dengue endemic areas. Good understanding of dengue transmission sites is a critical factor to implement effective vector control measures.

Methods

A cohort of 1,811 students from 10 schools in rural, semi-rural and semi-urban Thailand participated in this study. Seroconversion data and location of participants’ residences and schools were recorded to determine spatial patterns of dengue infections. Blood samples were taken to confirm dengue infections in participants at the beginning and the end of school term. Entomological factors included a survey of adult mosquito density using a portable vacuum aspirator during the school term and a follow up survey of breeding sites of Aedes vectors in schools after the school term. Clustering analyses were performed to detect spatial aggregation of dengue infections among participants.

Results

A total of 57 dengue seroconversions were detected among the 1,655 participants who provided paired blood samples. Of the 57 confirmed dengue infections, 23 (40.0%) occurred in students from 6 (6.8%) of the 88 classrooms in 10 schools. Dengue infections did not show significant clustering by residential location in the study area. During the school term, a total of 66 Aedes aegypti mosquitoes were identified from the 278 mosquitoes caught in 50 classrooms of the 10 schools. In a follow-up survey of breeding sites, 484 out of 2,399 water containers surveyed (20.2%) were identified as active mosquito breeding sites.

Discussion and Conclusion

Our findings suggest that dengue infections were clustered among schools and among classrooms within schools. The schools studied were found to contain a large number of different types of breeding sites. Aedes vector densities in schools were correlated with dengue infections and breeding sites in those schools. Given that only a small proportion of breeding sites in the schools were subjected to vector control measures (11%), this study emphasizes the urgent need to implement vector control strategies at schools, while maintaining efforts at the household level.

Maintenance of host DNA integrity in field-preserved mosquito (Diptera: Culicidae) blood meals for identification by DNA barcoding

Background

Determination of the interactions between hematophagous arthropods and their hosts is a necessary component to understanding the transmission dynamics of arthropod-vectored pathogens. Current molecular methods to identify hosts of blood-fed arthropods require the preservation of host DNA to serve as an amplification template. During transportation to the laboratory and storage prior to molecular analysis, genetic samples need to be protected from nucleases, and the degradation effects of hydrolysis, oxidation and radiation. Preservation of host DNA contained in field-collected blood-fed specimens has an additional caveat: suspension of the degradative effects of arthropod digestion on host DNA. Unless effective preservation methods are implemented promptly after blood-fed specimens are collected, host DNA will continue to degrade. Preservation methods vary in their efficacy, and need to be selected based on the logistical constraints of the research program.

Methods

We compared four preservation methods (cold storage at -20 °C, desiccation, ethanol storage of intact mosquito specimens and crushed specimens on filter paper) for field storage of host DNA from blood-fed mosquitoes across a range of storage and post-feeding time periods. The efficacy of these techniques in maintaining host DNA integrity was evaluated using a polymerase chain reaction (PCR) to detect the presence of a sufficient concentration of intact host DNA templates for blood meal analysis. We applied a logistic regression model to assess the effects of preservation method, storage time and post-feeding time on the binomial response variable, amplification success.

Results

Preservation method, storage time and post-feeding time all significantly impacted PCR amplification success. Filter papers and, to a lesser extent, 95 % ethanol, were the most effective methods for the maintenance of host DNA templates. Amplification success of host DNA preserved in cold storage at -20 °C and desiccation was poor.

Conclusions

Our data suggest that, of the methods tested, host DNA template integrity was most stable when blood meals were preserved using filter papers. Filter paper preservation is effective over short- and long-term storage, while ethanol preservation is only suitable for short-term storage. Cold storage at -20 °C, and desiccation of blood meal specimens, even for short time periods, should be avoided.

Fitting the Incidence Data from the City of Campinas, Brazil, Based on Dengue Transmission Modellings Considering Time-Dependent Entomological Parameters

Four time-dependent dengue transmission models are considered in order to fit the incidence data from the City of Campinas, Brazil, recorded from October 1^st 1995 to September 30^th 2012. The entomological parameters are allowed to depend on temperature and precipitation, while the carrying capacity and the hatching of eggs depend only on precipitation. The whole period of incidence of dengue is split into four periods, due to the fact that the model is formulated considering the circulation of only one serotype. Dengue transmission parameters from human to mosquito and mosquito to human are fitted for each one of the periods. The time varying partial and overall effective reproduction numbers are obtained to explain the incidence of dengue provided by the models.

Spatial variation of insecticide resistance in the dengue vector Aedes aegypti presents unique vector control challenges

BACKGROUND

Dengue is a major public health problem in Mexico, where the use of chemical insecticides to control the principal dengue vector, Aedes aegypti, is widespread. Resistance to insecticides has been reported in multiple sites, and the frequency of kdr mutations associated with pyrethroid resistance has increased rapidly in recent years. In the present study, we characterized patterns of insecticide resistance in Ae. aegypti populations in five small towns surrounding the city of Merida, Mexico.

METHODS

A cross-sectional, entomological survey was performed between June and August 2013 in 250 houses in each of the five towns. Indoor resting adult mosquitoes were collected in all houses and four ovitraps were placed in each study block. CDC bottle bioassays were conducted using F0-F2 individuals reared from the ovitraps and kdr allele (Ile1016 and Cys1534) frequencies were determined.

RESULTS

High, but varying, levels of resistance to chorpyrifos-ethyl was detected in all study towns, complete susceptibility to bendiocarb in all except one town, and variations in resistance to deltamethrin between towns, ranging from 63-88% mortality. Significant associations were detected between deltamethrin resistance and the presence of both kdr alleles. Phenotypic resistance was highly predictive of the presence of both alleles, however, not all mosquitoes containing a mutant allele were phenotypically resistant. An analysis of genotypic differentiation (exact G test) between the five towns based on the adult female Ae. aegypti collected from inside houses showed highly significant differences (p < 0.0001) between genotypes for both loci. When this was further analyzed to look for fine scale differences at the block level within towns, genotypic differentiation was significant for both loci in San Lorenzo (Ile1016, p = 0.018 and Cys1534, p = 0.007) and for Ile1016 in Acanceh (p = 0.013) and Conkal (p = 0.031).

CONCLUSIONS

The results from this study suggest that 3 years after switching chemical groups, deltamethrin resistance and a high frequency of kdr alleles persisted in Ae. aegypti populations. The spatial variation that was detected in both resistance phenotypes and genotypes has practical implications, both for vector control operations as well as insecticide resistance management strategies.

The Risk of Dengue Virus Transmission in Dar es Salaam, Tanzania during an Epidemic Period of 2014

Background

In 2010, 2012, 2013 and 2014 dengue outbreaks have been reported in Dar es Salaam, Tanzania. However, there is no comprehensive data on the risk of transmission of dengue in the country. The objective of this study was to assess the risk of transmission of dengue in Dar es Salaam during the 2014 epidemic.

Methodology/Principal Findings

This cross-sectional study was conducted in Dar es Salaam, Tanzania during the dengue outbreak of 2014. The study involved Ilala, Kinondoni and Temeke districts. Adult mosquitoes were collected using carbon dioxide-propane powered Mosquito Magnet Liberty Plus traps. In each household compound, water-holding containers were examined for mosquito larvae and pupae. Dengue virus infection of mosquitoes was determined using real-time reverse transcription polymerase chain reaction (qRT-PCR). Partial amplification and sequencing of dengue virus genome in infected mosquitoes was performed. A total of 1,000 adult mosquitoes were collected. Over half (59.9%) of the adult mosquitoes were collected in Kinondoni. Aedes aegypti accounted for 17.2% of the mosquitoes of which 90.6% were from Kinondoni. Of a total of 796 houses inspected, 38.3% had water-holding containers in their premises. Kinondoni had the largest proportion of water-holding containers (57.7%), followed by Temeke (31.4%) and Ilala (23.4%). The most common breeding containers for the Aedes mosquitoes were discarded plastic containers and tires. High Aedes infestation indices were observed for all districts and sites, with a house index of 18.1% in Ilala, 25.5% in Temeke and 35.3% in Kinondoni. The respective container indices were 77.4%, 65.2% and 80.2%. Of the reared larvae and pupae, 5,250 adult mosquitoes emerged, of which 61.9% were Ae. aegypti. Overall, 27 (8.18) of the 330 pools of Ae. aegypti were positive for dengue virus. On average, the overall maximum likelihood estimate (MLE) indicates pooled infection rate of 8.49 per 1,000 mosquitoes (95%CI = 5.72–12.16). There was no significant difference in pooled infection rates between the districts. Dengue viruses in the tested mosquitoes clustered into serotype 2 cosmopolitan genotype.

Conclusions/Significance

Ae. aegypti is the main vector of dengue in Dar es Salaam and breeds mainly in medium size plastic containers and tires. The Aedes house indices were high, indicating that the three districts were at high risk of dengue transmission. The 2014 dengue outbreak was caused by Dengue virus serotype 2. The high mosquito larval and pupal indices in the area require intensification of vector surveillance along with source reduction and health education.

Until 2010, little was known about Dengue in Tanzania. Since then, four outbreaks have been reported in Dar es Salaam City. This study was therefore carried out to assess the risk of transmission of dengue in Dar es Salaam during an outbreak in 2014. In this study adult mosquitoes were collected using carbon dioxide-propane powered traps. In addition, household compounds were visited and all water-holding containers examined for presence of mosquito larvae and pupae. Mosquito virus infection was determined using real-time reverse transcription polymerase chain reaction (qRT-PCR). Of the total of 1,000 adult mosquitoes collected, Aedes aegypti accounted for 17.2%. A total of 796 houses were inspected and 38.3% had water-holding containers in their premises. The most common breeding containers for the Aedes mosquitoes were discarded plastic containers and tires. High Aedes infestation indices were observed for all districts and sites, with a house and container indices ranging from 18.1–25.5% and 65.2–80.2%, respectively. The Breteaux indices were 30.6, 20.8 and 25.3 in Ilala, Kinondoni and Temeke, respectively. An overall 8.18% of mosquito pools were infected with dengue virus serotype 2. The overall maximum likelihood estimate of pooled infection rate of 8.49 per 1,000 mosquitoes was observed. This information is useful for the design of appropriate vector surveillance and control strategies in the City of Dar es Salaam.

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.

Schools as Potential Risk Sites for Vector-Borne Disease Transmission: Mosquito Vectors in Rural Schools in Two Municipalities in Colombia

Dengue and other vector-borne diseases are of great public health importance in Colombia. Vector surveillance and control activities are often focused at the household level. Little is known about the importance of nonhousehold sites, including schools, in maintaining vector-borne disease transmission. The objectives of this paper were to determine the mosquito species composition in rural schools in 2 municipalities in Colombia and to assess the potential risk of vector-borne disease transmission in school settings. Entomological surveys were carried out in rural schools during the dry and rainy seasons of 2011. A total of 12 mosquito species were found: Aedes aegypti, Anopheles pseudopunctipennis, Culex coronator, Cx. quinquefasciatus, and Limatus durhamii in both immature and adult forms; Ae. fluviatilis, Cx. nigripalpus, Cx. corniger, and Psorophora ferox in immature forms only; and Ae. angustivittatus, Haemagogus equinus, and Trichoprosopon lampropus in adult forms only. The most common mosquito species was Cx. quinquefasciatus. Classrooms contained the greatest abundance of adult female Ae. aegypti and Cx. quinquefasciatus. The most common Ae. aegypti breeding sites were containers classified as "others" (e.g., cans), followed by containers used for water storage. A high level of Ae. aegypti infestation was found during the wet season. Our results suggest that rural schools are potentially important foci for the transmission of dengue and other mosquito-borne diseases. We propose that public health programs should be implemented in rural schools to prevent vector-borne diseases.

Clustering, climate and dengue transmission

Dengue is currently the most rapidly spreading vector-borne disease, with an increasing burden over recent decades. Currently, neither a licensed vaccine nor an effective anti-viral therapy is available, and treatment largely remains supportive. Current vector control strategies to prevent and reduce dengue transmission are neither efficient nor sustainable as long-term interventions. Increased globalization and climate change have been reported to influence dengue transmission. In this article, we reviewed the non-climatic and climatic risk factors which facilitate dengue transmission. Sustainable and effective interventions to reduce the increasing threat from dengue would require the integration of these risk factors into current and future prevention strategies, including dengue vaccination, as well as the continuous support and commitment from the political and environmental stakeholders.

Evolution of dengue disease and entomological monitoring in Santa Cruz, Bolivia 2002 - 2008

BACKGROUND

In the context of a rapid increase of dengue cases in the Americas, a monitoring system based on systematic serological control (IgM) of patients consulting for suspected dengue was developed in Bolivia at the end of the 1990s. In the most affected city of Santa Cruz, this system was complemented by an entomological surveillance program based on periodical search for immature stages of Aedes aegypti in dwelling water-holding containers. Here, we analyze these data and describe dengue patterns over 6 years (2002-2008), highlighting the spatial distribution of patients and vectors.

METHODOLOGY /PRINCIPAL FINDINGS

Data mining concerned six annual epidemic cycles (2002-2008), with continuous serological and clinical results and entomological data from 16 surveys, examined at the scales of 36 urban areas and four concentric areas covering the entire city. Annual incidence varied from 0.28‰ to 0.95‰; overall incidence was higher in women and adults, and dengue dynamics followed successive periods of high (January-June) and low (July-December) transmission. Lower numbers of cases from the city center to the periphery were observed, poorly related to the more homogeneous and permanent distribution of A. aegypti. "Plant pots" were a major vector source in the city center, and "Tires" and "Odds and ends" beyond the second ring of the city.

CONCLUSIONS/SIGNIFICANCE

Over the years, the increasing trend of dengue cases has been highlighted as well as its widespread distribution over the entire city, but an underestimation of the number of cases is strongly suspected. Contrary to popular belief, the city center appears more affected than the periphery, and dengue is not particularly related to waste. Interestingly, the clinical diagnosis of dengue by physicians improved over the years, whatever the gender, age and residential area of suspected cases.

Use of insecticide-treated school uniforms for prevention of dengue in schoolchildren: a cost-effectiveness analysis

BACKGROUND

Dengue-related illness is a leading cause of hospitalization and death, particularly among children. Practical, acceptable and affordable measures are urgently needed to protect this age group. Schools where children spend most of their day is proposed as an ideal setting to implement preventive strategies against day-biting Aedes mosquitoes. The use of insecticide-treated school uniforms is a promising strategy currently under investigation.

METHODS

Using a decision-analytic model, we evaluated the cost-effectiveness of the use of insecticide-treated school uniforms for prevention of dengue, compared with a "do-nothing" alternative, in schoolchildren from the societal perspective. We explored how the potential economic value of the intervention varied under various scenarios of intervention effectiveness and cost, as well as dengue infection risk in school-aged children, using data specific to Thailand.

RESULTS

At an average dengue incidence rate of 5.8% per year in school-aged children, the intervention was cost-effective (ICER≤$16,440) in a variety of scenarios when the intervention cost per child was $5.3 or less and the intervention effectiveness was 50% or higher. In fact, the intervention was cost saving (ICER<0) in all scenarios in which the intervention cost per child was $2.9 or less per year and the intervention effectiveness was 50% or higher. The results suggested that this intervention would be of no interest to Thai policy makers when the intervention cost per child was $10.6 or higher per year regardless of intervention effectiveness (ICER>$16,440).

CONCLUSIONS

Our results present the potential economic value of the use of insecticide-treated uniforms for prevention of dengue in schoolchildren in a typical dengue endemic setting and highlight the urgent need for additional research on this intervention.

Exploratory space-time analysis of dengue incidence in Trinidad: a retrospective study using travel hubs as dispersal points, 1998-2004

BACKGROUND

Dengue is an acute arboviral disease responsible for most of the illness and death in tropical and subtropical regions. Over the last 25 years there has been increase epidemic activity of the disease in the Caribbean, with the co-circulation of multiple serotypes. An understanding of the space and time dynamics of dengue could provide health agencies with important clues for reducing its impact.

METHODS

Dengue Haemorrhagic Fever (DHF) cases observed for the period 1998-2004 were georeferenced using Geographic Information System software. Spatial clustering was calculated for individual years and for the entire study period using the Nearest Neighbor Index. Space and time interaction between DHF cases was determined using the Knox Test while the Nearest Neighbor Hierarchical method was used to extract DHF hot spots. All space and time distances calculated were validated using the Pearson r significance test.

RESULTS

Results shows that (1) a decrease in mean distance between DHF cases correlates with activity leading up to an outbreak, (2) a decrease in temporal distance between DHF cases leads to increased geographic spread of the disease, with an outbreak occurrence about every 2 years, and (3) a general pattern in the movement of dengue incidents from more rural to urban settings leading up to an outbreak with hotspot areas associated with transportation hubs in Trinidad.

CONCLUSION

Considering only the spatial dimension of the disease, results suggest that DHF cases become more concentrated leading up to an outbreak. However, with the additional consideration of time, results suggest that when an outbreak occurs incidents occur more rapidly in time leading to a parallel increase in the rate of distribution of the disease across space. The results of this study can be used by public health officers to help visualize and understand the spatial and temporal patterns of dengue, and to prepare warnings for the public. Dengue space-time patterns and hotspot detection will provide useful information to support public health officers in their efforts to control and predict dengue spread over critical hotspots allowing better allocation of resources.

Household use of insecticide consumer products in a dengue-endemic area in México

OBJECTIVES

To evaluate the household use of insecticide consumer products to kill mosquitoes and other insect pests, as well as the expenditures for using these products, in a dengue-endemic area of México.

METHODS

A questionnaire was administered to 441 households in Mérida City and other communities in Yucatán to assess household use of insecticide consumer products.

RESULTS

A total of 86.6% of surveyed households took action to kill insect pests with consumer products. The most commonly used product types were insecticide aerosol spray cans (73.6%), electric plug-in insecticide emitters (37.4%) and mosquito coils (28.3%). Mosquitoes were targeted by 89.7% of households using insecticide aerosol spray cans and >99% of households using electric plug-in insecticide emitters or mosquito coils. Products were used daily or every 2 days in most of the households for insecticide aerosol spray cans (61.4%), electric plug-in insecticide emitters (76.2%) and mosquito coils (82.1%). For all products used to kill insect pests, the median annual estimated expenditure per household that took action was 408 Mexican pesos ($MXN), which corresponded to approximately 31 $US. These numbers are suggestive of an annual market in excess of 75 million $MXN (>5.7 million $US) for Mérida City alone.

CONCLUSION

Mosquitoes threaten human health and are major nuisances in homes in the study area in México. Households were found to have taken vigorous action to kill mosquitoes and other insect pests and spent substantial amounts of money on insecticide consumer products.

Urban Mosquito Fauna in Mérida City, México: Immatures Collected from Containers and Storm-water Drains/Catch Basins

We examined the species composition and temporal occurrence of immature mosquitoes in containers and storm-water drains/catch basins from November 2011 to June 2013 in Mérida City, México. A wide range of urban settings were examined, including residential premises, vacant lots, parking lots, and streets or sidewalks with storm-water drains/catch basins. In total, 111,776 specimens of 15 species were recorded. The most commonly collected species were Aedes (Stegomyia) aegypti (L.) (n = 60,961) and Culex quinquefasciatus Say (45,702), which together accounted for 95.4% of the immatures collected. These species were commonly encountered during both rainy and dry seasons, whereas most other mosquito species were collected primarily during the rainy season. Other species collected were Aedes (Howardina) cozumelensis Diaz Najera, Aedes (Ochlerotatus) taeniorhynchus (Wiedemann), Aedes (Ochlerotatus) trivittatus (Coquillett), Culex coronator Dyar and Knab, Culex interrogator Dyar and Knab, Culex lactator Dyar and Knab, Culex nigripalpus Theobald, Culex salinarius Coquillett, Culex tarsalis Coquillett, Culex thriambus Dyar, Haemagogus equinus Theobald, Limatus durhamii Theobald, and Toxorhynchites rutilus (Coquillett). The greatest number of species was recorded from vacant lots (n = 11), followed by storm-water drains/catch basins (nine) and residential premises (six). Our study demonstrated that the heterogeneous urban environment in Mérida City supports a wide range of mosquito species, many of which are nuisance biters of humans and/or capable of serving as vectors of pathogens affecting humans or domestic animals. We also briefly reviewed the medical importance of the encountered mosquito species.

Vacant lots: productive sites for Aedes (Stegomyia) aegypti (Diptera: Culicidae) in Mérida City, México

We assessed the potential for vacant lots and other nonresidential settings to serve as source environments for Aedes (Stegomyia) aegypti (L.) (Diptera: Culicidae) in Mérida City, México. Mosquito immatures were collected, during November 2011-June 2013, from residential premises (n = 156 site visits) and nonresidential settings represented by vacant lots (50), parking lots (18), and streets or sidewalks (28). Collections totaled 46,025 mosquito immatures of 13 species. Ae. aegypti was the most commonly encountered species accounting for 81.0% of total immatures, followed by Culex quinquefasciatus Say (12.1%). Site visits to vacant lots (74.0%) were more likely to result in collection of Ae. aegypti immatures than residential premises (35.9%). Tires accounted for 75.5% of Ae. aegypti immatures collected from vacant lots. Our data suggest that vacant lots should be considered for inclusion in mosquito surveillance and control efforts in Mérida City, as they often are located near homes, commonly have abundant vegetation, and frequently harbor accumulations of small and large discarded water-holding containers that we now have demonstrated to serve as development sites for immature mosquitoes. In addition, we present data for associations of immature production with various container characteristics, such as storage capacity, water quality, and physical location in the environment.

Indoor volatiles of primary school classrooms in Tapachula, Chiapas, Mexico, are attractants to Aedes aegypti females

We determined the behavioral response of Aedes aegypti females to volatile compounds collected in indoor primary school classrooms. Volatiles were collected from classrooms from 0800 through 1030 h and 1130 through 1400 h in urban and rural schools in Tapachula, Chiapas, Mexico. Female responses to volatiles were assessed in a Y-tube olfactometer. Chemical compounds were identified using gas chromatography-mass spectrometer analysis. Volatiles from both schools were attractive when compared against their control. When such volatiles were compared, those from the rural school were more attractive than the ones from the urban school. Chromatographic profiles were similar between schools; however, the rural school showed more compounds. Attraction of Ae. aegypti females toward volatiles of primary school classrooms might increase dengue transmission probabilities in those sites.

Dengue virus type 4 in Niterói, Rio de Janeiro: the role of molecular techniques in laboratory diagnosis and entomological surveillance

In Niterói, state of Rio de Janeiro, dengue virus type 4 (DENV-4) was isolated for the first time in March 2011. We analysed the laboratory findings of the first cases and evaluated the use of molecular techniques for the detection of DENV-4 in Aedes aegypti that were field-caught. Conventional reverse transcriptase-polymerase chain reaction (RT-PCR) and Simplexa™ Dengue real-time RT-PCR confirmed DENV-4 infection in all cases. Additionally, DENV-4 was confirmed in a female Ae. aegypti with 1.08 x 10(3) copies/mL of virus, as determined by quantitative real-time RT-PCR. This is the first time the Simplexa™ Dengue real-time assay has been used for the classification of cases of infection and for entomological investigations. The use of these molecular techniques was shown to be important for the surveillance of dengue in humans and vectors.

Towards a Casa Segura: a consumer product study of the effect of insecticide-treated curtains on Aedes aegypti and dengue virus infections in the home

The home, or domicile, is the principal environment for transmission of dengue virus (DENV) between humans and mosquito vectors. Community-wide distribution of insecticide-treated curtains (ITCs), mimicking vector control program-driven interventions, has shown promise to reduce DENV infections. We conducted a Casa Segura consumer product intervention study in Mérida, Mexico to determine the potential to reduce intradomicillary DENV transmission through ITC use in individual homes. Dengue virus infections in mosquitoes and in humans were reduced in homes with ITCs in one of two study subareas. Overall, ITCs reduced intradomicillary DENV transmission; ITC homes were significantly less likely to experience multiple DENV infections in humans than NTC homes. Dengue virus-infected Aedes aegypti females were reduced within the ITC homes where curtain use was highest. Some homes yielded up to nine infected Ae. aegypti females. This study provides insights regarding best practices for Casa Segura interventions to protect homes from intradomicillary DENV transmission.

Aedes (Stegomyia) aegypti in the continental United States: a vector at the cool margin of its geographic range

After more than a half century without recognized local dengue outbreaks in the continental United States, there were recent outbreaks of autochthonous dengue in the southern parts of Texas (2004-2005) and Florida (2009-2011). This dengue reemergence has provoked interest in the extent of the future threat posed by the yellow fever mosquito, Aedes (Stegomyia) aegypti (L.), the primary vector of dengue and yellow fever viruses in urban settings, to human health in the continental United States. Ae. aegypti is an intriguing example of a vector species that not only occurs in the southernmost portions of the eastern United States today but also is incriminated as the likely primary vector in historical outbreaks of yellow fever as far north as New York, Philadelphia, and Boston, from the 1690s to the 1820s. For vector species with geographic ranges limited, in part, by low temperature and cool range margins occurring in the southern part of the continental United States, as is currently the case for Ae. aegypti, it is tempting to speculate that climate warming may result in a northward range expansion (similar to that seen for Ixodes tick vectors of Lyme borreliosis spirochetes in Scandinavia and southern Canada in recent decades). Although there is no doubt that climate conditions directly impact many aspects of the life history of Ae. aegypti, this mosquito also is closely linked to the human environment and directly influenced by the availability of water-holding containers for oviposition and larval development. Competition with other container-inhabiting mosquito species, particularly Aedes (Stegomyia) albopictus (Skuse), also may impact the presence and local abundance of Ae. aegypti. Field-based studies that focus solely on the impact of weather or climate factors on the presence and abundance of Ae. aegypti, including assessments of the potential impact of climate warming on the mosquito's future range and abundance, do not consider the potential confounding effects of socioeconomic factors or biological competitors for establishment and proliferation of Ae. aegypti. The results of such studies therefore should not be assumed to apply in areas with different socioeconomic conditions or composition of container-inhabiting mosquito species. For example, results from field-based studies at the high altitude cool margins for Ae. aegypti in Mexico's central highlands or the Andes in South America cannot be assumed to be directly applicable to geographic areas in the United States with comparable climate conditions. Unfortunately, we have a very poor understanding of how climatic drivers interact with the human landscape and biological competitors to impact establishment and proliferation of Ae. aegypti at the cool margin of its range in the continental United States. A first step toward assessing the future threat this mosquito poses to human health in the continental United States is to design and conduct studies across strategic climatic and socioeconomic gradients in the United States (including the U.S.-Mexico border area) to determine the permissiveness of the coupled natural and human environment for Ae. aegypti at the present time. This approach will require experimental studies and field surveys that focus specifically on climate conditions relevant to the continental United States. These studies also must include assessments of how the human landscape, particularly the impact of availability of larval developmental sites and the permissiveness of homes for mosquito intrusion, and the presence of other container-inhabiting mosquitoes that may compete with Ae. aegypti for larval habitat affects the ability of Ae. aegypti to establish and proliferate. Until we are armed with such knowledge, it is not possible to meaningfully assess the potential for climate warming to impact the proliferation potential for Ae. aegypti in the United States outside of the geographic areas where the mosquito already is firmly established, and even less so for dengue virus transmission and dengue disease in humans.

House-to-house human movement drives dengue virus transmission

Dengue is a mosquito-borne disease of growing global health importance. Prevention efforts focus on mosquito control, with limited success. New insights into the spatiotemporal drivers of dengue dynamics are needed to design improved disease-prevention strategies. Given the restricted range of movement of the primary mosquito vector, Aedes aegypti, local human movements may be an important driver of dengue virus (DENV) amplification and spread. Using contact-site cluster investigations in a case-control design, we demonstrate that, at an individual level, risk for human infection is defined by visits to places where contact with infected mosquitoes is likely, independent of distance from the home. Our data indicate that house-to-house human movements underlie spatial patterns of DENV incidence, causing marked heterogeneity in transmission rates. At a collective level, transmission appears to be shaped by social connections because routine movements among the same places, such as the homes of family and friends, are often similar for the infected individual and their contacts. Thus, routine, house-to-house human movements do play a key role in spread of this vector-borne pathogen at fine spatial scales. This finding has important implications for dengue prevention, challenging the appropriateness of current approaches to vector control. We argue that reexamination of existing paradigms regarding the spatiotemporal dynamics of DENV and other vector-borne pathogens, especially the importance of human movement, will lead to improvements in disease prevention.

Nature, nurture and evolution of intra-species variation in mosquito arbovirus transmission competence

Mosquitoes vary in their competence or ability to transmit arthropod-borne viruses (arboviruses). Many arboviruses cause disease in humans and animals. Identifying the environmental and genetic causes of variation in mosquito competence for arboviruses is one of the great challenges in public health. Progress identifying genetic (nature) and environmental (nurture) factors influencing mosquito competence for arboviruses is reviewed. There is great complexity in the various traits that comprise mosquito competence. The complex interactions between environmental and genetic factors controlling these traits and the factors shaping variation in Nature are largely unknown. The norms of reaction of specific genes influencing competence, their distributions in natural populations and the effects of genetic polymorphism on phenotypic variation need to be determined. Mechanisms influencing competence are not likely due to natural selection because of the direct effects of the arbovirus on mosquito fitness. More likely the traits for mosquito competence for arboviruses are the effects of adaptations for other functions of these competence mechanisms. Determining these other functions is essential to understand the evolution and distributions of competence for arboviruses. This information is needed to assess risk from mosquito-borne disease, predict new mosquito-arbovirus systems, and provide novel strategies to mitigate mosquito-borne arbovirus transmission.

Aedes (Stegomyia) aegypti and Aedes (Howardina) cozumelensis in Yucatán State, México, with a summary of published collection records for Ae. cozumelensis

We collected mosquito immatures from artificial containers during 2010-2011 from 26 communities, ranging in size from small rural communities to large urban centers, located in different parts of Yucatán State in southeastern México. The arbovirus vector Aedes (Stegomyia) aegypti was collected from all 26 examined communities, and nine of the communities also yielded another container-inhabiting Aedes mosquito: Aedes (Howardina) cozumelensis. The communities from which Ae. cozumelensis were collected were all small rural communities (<6,000 inhabitants) in the north-central part of Yucatán State. These new collection records for Ae. cozumelensis demonstrate that this mosquito has a far broader geographic range in the Yucatán Peninsula than previously known. Ae. cozumelensis immatures were collected from both residential premises and cemeteries, with specimens recovered from rock holes as well as various artificial containers including metal cans, flower vases, buckets, tires, and a water storage tank. The co-occurrence with Ae. aegypti in small rural communities poses intriguing questions regarding linkages between these mosquitoes, including the potential for direct competition for larval development sites. Additional studies are needed to determine how commonly Ae. cozumelensis feeds on human blood and whether it is naturally infected with arboviruses or other pathogens of medical or veterinary importance. We also summarize the published records for Ae. cozumelensis, which are restricted to collections from México's Yucatán Peninsula and Belize, and uniformly represent geographic locations where Ae. aegypti can be expected to occur.

Diarrhea and dengue control in rural primary schools in Colombia: study protocol for a randomized controlled trial

BACKGROUND

Diarrheal diseases and dengue fever are major global health problems. Where provision of clean water is inadequate, water storage is crucial. Fecal contamination of stored water is a common source of diarrheal illness, but stored water also provides breeding sites for dengue vector mosquitoes. Poor household water management and sanitation are therefore potential determinants of both diseases. Little is known of the role of stored water for the combined risk of diarrhea and dengue, yet a joint role would be important for developing integrated control and management efforts. Even less is known of the effect of integrating control of these diseases in school settings. The objective of this trial was to investigate whether interventions against diarrhea and dengue will significantly reduce diarrheal disease and dengue entomological risk factors in rural primary schools.

METHODS/DESIGN

This is a 2×2 factorial cluster randomized controlled trial. Eligible schools were rural primary schools in La Mesa and Anapoima municipalities, Cundinamarca, Colombia. Eligible pupils were school children in grades 0 to 5. Schools were randomized to one of four study arms: diarrhea interventions (DIA); dengue interventions (DEN); combined diarrhea and dengue interventions (DIADEN); and control (C). Schools were allocated publicly in each municipality (strata) at the start of the trial, obviating the need for allocation concealment. The primary outcome for diarrhea is incidence rate of diarrhea in school children and for dengue it is density of adult female Aedes aegypti per school. Approximately 800 pupils from 34 schools were enrolled in the trial with eight schools in the DIA arm, nine in the DEN, eight in the DIADEN, and nine in the control arms. The trial status as of June 2012 was: completed baseline data collections; enrollment, randomization, and allocation of schools. The trial was funded by the Research Council of Norway and the Lazos de Calandaima Foundation.

DISCUSSION

This is the first trial investigating the effect of a set of integrated interventions to control both dengue and diarrhea. This is also the first trial to study the combination of diarrhea-dengue disease control in school settings.

TRIAL REGISTRATION

Current Controlled Trials ISRCTN40195031.