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

Abstract

Background: Transovarial transmission of dengue virus in Aedes spp. mosquitoes is considered an important mechanism for the maintenance of the virus in nature and may be implicated in the occurrence of outbreaks and epidemics of the disease. However, there are few studies involving transovarial transmission and viral vector monitoring as a surveillance tool and control strategy. The present study evaluated transovarial transmission of dengue virus in Aedes aegypti populations as a xenomonitoring strategy in municipalities of the Amazonas state.

Results: Aedes sp. eggs (13.164) were collected, with 30% viability of third- and fourth-instar larvae. Transovarial transmission of DENV was detected in all municipalities. The transovarial infection rate (TOR) in the municipalities was 46% of the DENV positive samples. The minimum infection rate (MIR) was 17.7 in the state, varying from 11.4 to 24.1 per 1,000 larvae tested in the respective municipalities. Four DENV serotypes were identified, with DENV I and IV being present in all municipalities investigated. The number of reported dengue fever cases varied during this period.

Conclusions: Our results suggest that transovarial transmission may be an important mechanism for the maintenance and spreading of the disease in Amazonas municipalities. Using qRT-PCR, it was possible to identify the four DENV serotypes in larval samples. The methodology used in the present study proved suitable as a DENV xenomonitoring model in immature mosquitoes, contributing to the development of systems for early detection of viral circulation and predictive models for the occurrence of outbreaks and epidemics of this disease.

Trial registration: CAAE34025414200005015 .

Keywords: Aedes aegypti; Control; Dengue; Monitoring; Ovitraps; Transovarial transmission; Xenosurveillance.

Fig. 1

Map showing the geographical localization of the sites where egg collection was performed in municipalities of the Amazonas State: 3,538,387 inhabitants, emphasizing the grids selected to place the ovitraps. a Tabatinga (52,272 inhabitants). b Coari 75,965 (inhabitants). c Itacoatiara (86,839 inhabitants). d Manaus - AM (Parque 10 de Novembro neighborhood; 41,256 inhabitants)

Fig. 2

Reported dengue fever cases according to probable site of infection in the municipalities where the collection was performed, Amazonas (Brazil), between June 2013 and June 2014, by epidemiological week, and egg density index (EDI). Legend: Lines, number of dengue fever cases; Bars, egg density index (EDI)