Daily probability of survival and frequency of human blood- feeding are the 2 most sensitive components of a mosquito's role in pathogen transmission. Most models of vector-borne diseases assume that survival and feeding behavior do not change as mosquitoes grow older. Until now this assumption has not been strongly challenged because accurate methods for estimating age across epidemiologically different portions of a mosquito's lifetime or identifying the people a mosquito had bitten were not available; measurement of mosquito chronological age and host- feeding patterns were difficult or impossible. We have developed novel, more accurate methods that can determine for the 1st time if survival and frequency of host contact increase as mosquito vectors grow older and become infective. In this renewal proposal we will use these methods to test the hypothesis that Aedes aegypti's daily probability of survival and frequency of human blood-feeding increase as mosquitoes age. Older female Ae. aegypti are epidemiologically most important, because they are more likely to be infected with and transmit dengue virus than younger mosquitoes. To determine the chronological age of wild mosquitoes up to approximately 21 days of age we analyze cuticular hydrocarbons (CH). We can reconstruct mosquito blood- feeding behavior with a DNA fingerprinting procedure that identifies the person(s) from which a mosquito took its meal(s). High recapture rates in mark-recapture studies (approximately 30 percent) allow us to investigate survival, dispersal, and blood- feeding for free-ranging mosquitoes in the natural environment. Our study has 2 specific aims that we will carry out in northwestern Thailand, where Ae. aegypti-borne dengue virus is endemic.
In Aim 1 we will compare the observed age structure (CH age-grading) and feeding patterns (DNA fingerprinting) of wild mosquitoes to the patterns expected under the assumption that these components of transmission remain constant as mosquitoes grow older. Before directly testing our research hypothesis in Aim 2 we will define the limitations of our current mark- recapture methods and select the best procedure for subsequent experiments on age-dependent differences in survival, dispersal, and blood-feeding. In our last set of experiments we will directly test the idea that dynamics in survival and blood- feeding frequency increase with mosquito age by releasing 2 distinct age cohorts and comparing their recapture rates, survival, and blood-feeding behavior. Insecticide treatments at the end of each experiment will kill any surviving released mosquitoes before they could become infective and transmit virus.
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