Vírus dengue em larvas de Aedes aegypti e sua dinâmica de infestação, Roraima, Brasil

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.

Transovarial transmission of DENV in Aedes aegypti in the Amazon basin: a local model of xenomonitoring

“…Viral monitoring in mosquitoes has suggested that transovarial transmission rates (TOT) occur at low levels in nature [20, 32, 33, 37]. In 2008, in Roraima, Zeidler et al [32] performed an RT-PCR evaluation of 44 Ae.…”

“…In 2008, in Roraima, Zeidler et al [32] performed an RT-PCR evaluation of 44 Ae. aegypti larvae pools containing 1,172 larvae and were unable to detect the presence of DENV, even though the collection took place in areas with elevated transmission of the disease.…”

“…Several factors can contribute to failure in detecting TOT, including low sensitivity of the tests, inappropriate methodology, and mosquito sample maintenance issues, among others [39]. In addition, Zeidler et al [32] suggested that the method of viral detection in Ae. aegypti larvae is not the most suitable to estimate the risk of epidemics and that adult insects should be collected instead, providing increased sensitivity.…”

“…aegypti larvae, including replicates for each sample, for the detection and amplification of DENV. RNA extraction was performed as described in [32]. Following centrifugation, 140 μl of supernatant was processed for extraction of viral RNA using the QIAamp® Viral RNA mini Kit (31 Qiagen, Hilden, Germany) according to the manufacturer’s instructions [33].…”

“…qRT-PCR reactions were processed in a 7500 Fast Real Time PCR Systems (Applied Biosystems) thermal cycler as described in [32]. The plasmid DNA was then digested with Faun DIN Restriction Enzyme (Life Technologies, Carlsbad, USA) for 4 h. The GFX-Illustra® kit (GE Healthcare, Little Chalfont, UK) was used to purify the digested DNA, according to the manufacturer’s protocol.…”