Abstract
We performed a longitudinal study of adult survival of Anopheles darlingi, the most important vector in the Amazon, in a malarigenous frontier zone of Brazil. Survival rates were determined from both parous rates and multiparous dissections. Anopheles darlingi human biting rates, daily survival rates and expectation of life where higher in the dry season, as compared to the rainy season, and were correlated with malaria incidence. The biting density of mosquitoes that had survived long enough for completing at least one sporogonic cycle was related with the number of malaria cases by linear regression. Survival rates were the limiting factor explaining longitudinal variations in Plasmodium vivax malaria incidence and the association between adult mosquito survival and malaria was statistically significant by logistic regression (P<0.05). Survival rates were better correlated with malaria incidence than adult mosquito biting density. Mathematical modeling showed that P. falciparum and P. malariae were more vulnerable to changes in mosquito survival rates because of longer sporogonic cycle duration, as compared to P. vivax, which could account for the low prevalence of the former parasites observed in the study area. Population modeling also showed that the observed decreases in human biting rates in the wet season could be entirely explained by decreases in survival rates, suggesting that decreased breeding did not occur in the wet season, at the sites where adult mosquitoes were collected. For the first time in the literature, multivariate methods detected a statistically significant inverse relation (P<0.05) between the number of rainy days per month and daily survival rates, suggesting that rainfall may cause adult mortality.
Highlights
Malaria remains one of the most important infectious diseases in the world, and has reemerged in tropical regions that experience rapid population growth [1]
Fouque et al [7] have observed that peak malaria incidence in the Maroni region of French Guiana was associated with higher Anopheles darlingi survival rates, the most important vector in the Amazon [8,9,10] but data were not statistically significant
Rainfall appeared to be inversely related with daily survival rates, density of dangerously aged mosquitoes and malaria cases
Summary
Malaria remains one of the most important infectious diseases in the world, and has reemerged in tropical regions that experience rapid population growth [1]. The understanding of age composition of anopheline mosquito populations has been considered crucial for explaining transmission and evaluating the success of control efforts [2]. Little is known of age composition and survival rates of anopheline species in the Amazon region. Fouque et al [7] have observed that peak malaria incidence in the Maroni region of French Guiana was associated with higher Anopheles darlingi survival rates, the most important vector in the Amazon [8,9,10] but data were not statistically significant. The association of survival rates with malaria incidence was studied in detail
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