Abstract
OBJECTIVE: To detect the presence of dengue virus in larval forms of Aedes aegypti and to associate vector presence with rainfall and incidence of disease. METHODS: Eighteen households were randomly selected for egg collection in a neighborhood of the city of Boa Vista, Roraima, in Northern Brazil. Two oviposition traps were installed per home, and removed after one week. This was repeated on a monthly basis between November 2006 and May 2007. Trap positivity rate and egg density were calculated. Following the eclosion of 1,422 eggs, 44 pools of at least 30 larvae each were formed, which were evaluated for presence of dengue virus using RT-PCR and hemi-nested PCR. Dengue incidence rates in the period were correlated with rainfall rates. The association between these two variables and the number of eggs collected was determined using Pearson correlation. RESULTS: None of the pools tested positive for presence of dengue virus, despite the high incidence of dengue in the neighborhood during the studied period. The density of Ae. aegypti increased with rainfall, but was not correlated with incidence of dengue. CONCLUSIONS: The results suggest that transovarial transmission of dengue virus in mosquitoes occurs at a very low frequency, and therefore virus persistence in urban settings may not depend on such transmission. The mosquito population increased during the rainy season due to increased formation of breeding sites; the lack of correlation with incidence of dengue may be due to underestimation of incidence data during epidemics.
Highlights
The first dengue epidemic in Brazil to be confirmed by laboratory diagnosis took place in Boa Vista, Northern Brazil, in 1981-82
The results suggest that transovarial transmission of dengue virus in mosquitoes occurs at a very low frequency, and virus persistence in urban settings may not depend on such transmission
The mosquito population increased during the rainy season due to increased formation of breeding sites; the lack of correlation with incidence of dengue may be due to underestimation of incidence data during epidemics
Summary
The first dengue epidemic in Brazil to be confirmed by laboratory diagnosis took place in Boa Vista, Northern Brazil, in 1981-82. During this epidemic, dengue virus serotypes 1 and 4 were isolated. Beginning in 1982, an intensive vector control campaign took place which eradicated the vector from the region, and no epidemics were reported in Boa Vista until 1999. According to data from the Pan-American Health Association, the four dengue serotypes are currently in circulation in Venezuela, and there is a possibility of reintroduction of serotype 4 through this border
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