BackgroundChagas disease transmission by Triatoma dimidiata persists in Guatemala and elsewhere in Central America under undefined ecological, biological and social (eco-bio-social) conditions.MethodologyEco-bio-social risk factors associated with persistent domiciliary infestation were identified by a cross-sectional survey and qualitative participatory methods. Quantitative and qualitative data were generated regarding Trypanosoma cruzi reservoirs and triatomine hosts. Blood meal analysis and infection of insects, dogs and rodents were determined. Based on these data, multimodel inference was used to identify risk factors for domestic infestation with the greatest relative importance (>0.75).Principal FindingsBlood meal analysis showed that 64% of 36 bugs fed on chickens, 50% on humans, 17% on dogs; 24% of 34 bugs fed on Rattus rattus and 21% on Mus musculus. Seroprevalence among 80 dogs was 37%. Eight (17%) of 46 M. musculus and three (43%) of seven R. rattus from households with infected triatomines were infected with T. cruzi Distinct Typing Unit I. Results from interviews and participatory meetings indicated that vector control personnel and some householders perceived chickens roosting and laying eggs in the house as bug infestation risk factors. House construction practices were seen as a risk factor for bug and rodent infestation, with rodents being perceived as a pest by study participants. Multimodel inference showed that house infestation risk factors of high relative importance are dog density, mouse presence, interior wall plaster condition, dirt floor, tile roofing and coffee tree presence.Conclusions/SignificancePersistent house infestation is closely related to eco-bio-social factors that maintain productive T. dimidiata habitats associated with dogs, chickens and rodents. Triatomine, dog and rodent infections indicate active T. cruzi transmission. Integrated vector control methods should include actions that consider the role of peridomestic animals in transmission and community memberś level of knowledge, attitudes and practices associated with the disease and transmission process.

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BackgroundIntegrated vector management strategies depend on local eco-bio-social conditions, community participation, political will and inter-sectorial partnership. Previously identified risk factors for persistent Triatoma dimidiata infestation include the presence of rodents and chickens, tiled roofs, dirt floors, partial wall plastering and dog density.MethodsA community-based intervention was developed and implemented based on cyclical stakeholder and situational analyses. Intervention implementation and evaluation combined participatory action research and cluster randomized pre-test post-test experimental designs. The intervention included modified insecticide application, education regarding Chagas disease and risk factors, and participatory rodent control.ResultsAt final evaluation there was no significant difference in post-test triatomine infestation between intervention and control, keeping pre-test rodent and triatomine infestations constant. Knowledge levels regarding Chagas disease and prevention practices including rodent control, chicken management and health service access increased significantly only in intervention communities. The odds of nymph infection and rat infestation were 8.3 and 1.9-fold higher in control compared to intervention communities, respectively.ConclusionVector control measures without reservoir control are insufficient to reduce transmission risk in areas with persistent triatomine infestation. This integrated vector management program can complement house improvement initiatives by prioritizing households with risk factors such as tiled roofs. Requirement for active participation and multi-sectorial coordination poses implementation challenges.

Background The sterile insect technique (SIT) for use against mosquitoes consists of several steps including the production of the target species in large numbers, the separation of males and females, the sterilization of the males, and the packing, transport and release of the sterile males at the target site. The sterility of the males is the basis of the technique; for this, efficient and standardized irradiation methods are needed to ensure that the required level of sterility is reliably and reproducibly achieved. While several reports have found that certain biological factors, handling methods and varying irradiation procedures can alter the level of induced sterility in insects, few studies exist in which the methodologies are adequately described and discussed for the reproductive sterilization of mosquitoes. Numerous irradiation studies on mosquito pupae have resulted in varying levels of sterility. Therefore, we initiated a series of small-scale experiments to first investigate variable parameters that may influence dose-response in mosquito pupae, and secondly, identify those factors that potentially have a significantly large effect and need further attention. Methods In this study, we compiled the results of a series of experiments investigating variable parameters such as pupal age (Aedes aegypti), pupal size (Ae. aegypti), geographical origin of mosquito strains (Ae. aegypti and Ae. albopictus), exposure methods (in wet versus dry conditions, Ae. albopictus) and subsequently in low versus high oxygen environments [submerged in water (low O2 (< 5 %)] and in air [high O2 (~ 21 %)] on the radiosensitivity of male pupae (Ae. aegypti, Ae. albopictus and Anopheles arabiensis). Results Results indicate that radiosensitvity of Ae. aegypti decreases with increasing pupal age (99% induced sterility in youngest pupae, compared to 93% in oldest pupae), but does not change with differences in pupal size (P = 0.94). Differing geographical origin of the same mosquito species did not result in variations in radiosensitivity in Ae. aegypti pupae [Brazil, Indonesia, France (La Reunion), Thailand] or Ae. albopictus [Italy, France (La Reunion)]. Differences in induced sterility were seen following irradiation of pupae that were in wet versus dry conditions, which led to further tests showing significant radioprotective effects of oxygen depletion during irradiation procedures in three tested mosquito species, as seen in other insects. Conclusions These findings infer the necessity to further evaluate significant factors and reassess dose-response for mosquitoes with controlled variables to be able to formulate protocols to achieve reliable and reproducible levels of sterility for application in the frame of the SIT.

Mosquito-borne viruses are emerging or re-emerging globally, afflicting millions of people around the world. Aedes aegypti, the yellow fever mosquito, is the principal vector of dengue, Zika, and chikungunya viruses, and has well-established populations across tropical and subtropical urban areas of the Americas, including the southern United States. While intense arboviral epidemics have occurred in Mexico and further south in the Americas, local transmission in the United States has been minimal. Here, we study Ae. aegypti and Culex quinquefasciatus host feeding patterns and vertebrate host communities in residential environments of South Texas to identify host-utilization relative to availability. Only 31% of Ae. aegypti blood meals were derived from humans, while 50% were from dogs and 19% from other wild and domestic animals. In Cx. quinquefasciatus, 67% of blood meals were derived from chicken, 22% came from dogs, 9% from various wild avian species, and 2% from other mammals including one human, one cat, and one pig. We developed a model for the reproductive number, R0, for Zika virus (ZIKV) in South Texas relative to northern Mexico using human disease data from Tamaulipas, Mexico. We show that ZIKV R0 in South Texas communities could be greater than one if the risk of human exposure to Ae. aegypti bites in these communities is at least 60% that of Northern Mexico communities. The high utilization of non-human vertebrates and low risk of human exposure in South Texas diminishes the outbreak potential for human-amplified urban arboviruses transmitted by Ae. aegypti.

Aedes aegypti is the main vector of arboviral diseases such as dengue, chikungunya and Zika. A key feature for disease transmission modeling and vector control planning is adult mosquito dispersal. We studied Ae aegypti adult dispersal by conducting a mark-capture study of naturally occurring Ae. aegypti from discarded containers found along a canal that divided two residential communities in Donna, texas, USA. Stable isotopes were used to enrich containers with either 13 c or 15 n. Adult mosquitoes were collected outdoors in the yards of households throughout the communities with BG Sentinel 2 traps during a 12-week period. Marked mosquito pools with stable isotopes were used to estimate the mean distance travelled using three different approaches (Net, Strip or Circular) and the probability of detecting an isotopically marked adult at different distances from the larval habitat of origin. We consistently observed, using the three approaches that male (Net: 220 m, Strip: 255 m, Circular: 250 m) Ae. aegypti dispersed further in comparison to gravid (Net: 135 m, Strip: 176 m, Circular: 189 m) and unfed females (Net: 192 m, Strip: 213 m, Circular: 198 m). We also observed that marked male capture probability slightly increased with distance, while, for both unfed and gravid females, such probability decreased with distance. Using a unique study design documenting adult dispersal from natural larval habitat, our results suggest that Ae. aegypti adults disperse longer distances than previously reported. These results may help guide local vector control authorities in their fight against Ae. aegypti and the diseases it transmits, suggesting coverage of 200 m for the use of insecticides and innovative vector control tools.

Abstract Effective mosquito surveillance and management depend on a thorough understanding of the biology and feeding patterns unique to species and sex. Given that a propensity to sugar feed is necessary for some mosquito surveillance and newer control strategies, we sought to document the amount of total sugar in wild Aedes aegypti (L.) and Culex quinquefasciatus (Say) captured from five different locations in the Lower Rio Grande Valley (LRGV) of South Texas over 2 yr. We used Biogents Sentinel 2 (BGS2) traps in year 1 and aspirators, BGS2, and CDC resting traps in years 2 and 3 to collect adult mosquitoes. The hot anthrone test was used to quantify total sugar content in each mosquito. Additionally, the cold and hot anthrone tests were used to distinguish fructose content from total sugars for mosquitoes captured in 2019. Overall, Ae. aegypti females had significantly lower total sugar content than Ae. aegypti males as well as both sexes of Cx. quinquefasciatus. However, the percentage of Ae. aegypti positive for fructose consumption was four to eightfold higher than Ae. aegypti previously reported in other regions. The difference between locations was significant for males of both species, but not for females. Seasonality and trapping method also revealed significant differences in sugar content of captured mosquitoes. Our results reinforce that sugar feeding in female Ae. aegypti is less than Cx. quinquefasciatus, although not absent. This study provides necessary data to evaluate the potential effectiveness of sugar baits in surveillance and control of both Ae. aegypti and Cx. quinquefasciatus mosquitoes.

Background Anopheles arabiensis is one of the major malaria vectors that put millions of people in endemic countries at risk. Mass-rearing of this mosquito is crucial for strategies that use sterile insect technique to suppress vector populations. The sterile insect technique (SIT) package for this mosquito species is being developed by the Insect Pest Control Subprogramme of the Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture. To improve mass-rearing outcomes for An. arabiensis, the question of whether the egg production by females would be affected by the size of the adult holding cages, the source of the blood meal and the total number of pupae that could be loaded into the cages was addressed and finally the impact of adding additional pupae to the cage daily to maintain adult numbers on egg productivity assessed.MethodsMass production cages of two different volumes, two different sources of blood meal (bovine and porcine) and two different population densities (cages originally loaded with either 15,000 or 20,000 pupae) were tested and evaluated on the basis of eggs produced/cage or per female. Males and females pupae with a ratio of 1:1 were added to the cages at day 1 and 2 of pupation. The emerging adults had constant access to 5% sugar solution and blood fed via the Hemotek membrane feeding system. Eggs were collected either twice a week or daily. A generalized linear model was used to identify factors which gave significantly higher egg production.ResultsNeither cage volume nor blood meal source affected egg production per cage or per female. However, increasing population density to 20,000 pupae had a negative effect on eggs produced per cage and per female. Although high density negatively impacted egg production, adding 1000 daily additional pupae compensating for daily mortality resulted in a substantial increase in egg production. Moreover, in all tests the first and the third egg batches collected were significantly higher than others eggs batches. With the equipment and protocols described here and routinely used at the Insect Pest Control Laboratory (IPCL), it was possible to produce up to 120,000 eggs/cage/day.ConclusionThese results demonstrated that 15,000 is the optimal number of pupae to be loaded into the Anopheles Mass production cages. Under this condition, an average of 40 eggs per female was obtained for five gonotrophic cycles. However, an improvement in egg production can be achieved by daily addition, to the original 15,000 pupae, of one thousand pupae a day. Interestingly, feeding females with bovine or porcine blood using both large and small versions of the mass production cage did not affect egg productivity.