Occurrence of natural vertical transmission of dengue-2 and dengue-3 viruses in Aedes aegypti and Aedes albopictus in Fortaleza, Ceará, Brazil

Abstract

Background: Aedes aegypti and Aedes albopictus perform an important role in the transmission of the dengue virus to human populations, particularly in the tropical and subtropical regions of the world. Despite a lack of understanding in relation to the maintenance of the dengue virus in nature during interepidemic periods, the vertical transmission of the dengue virus in populations of A. aegypti and A. albopictus appears to be of significance in relation to the urban scenario of Fortaleza.

Methods: From March 2007 to July 2009 collections of larvae and pupae of Aedes spp were carried out in 40 neighborhoods of Fortaleza. The collections yielded 3,417 (91%) A. aegypti mosquitoes and 336 (9%) A. albopictus mosquitoes. Only pools containing females, randomly chosen, were submitted to the following tests indirect immunofluorescence (virus isolation), RT-PCR/nested-PCR and nucleotide sequencing at the C-prM junction of the dengue virus genome.

Results: The tests on pool 34 (35 A. albopictus mosquitoes) revealed with presence of DENV-3, pool 35 (50 A. aegypti mosquitoes) was found to be infected with DENV-2, while pool 49 (41 A. albopictus mosquitoes) revealed the simultaneous presence of DENV-2 and DENV-3. Based on the results obtained, there was a minimum infection rate of 0.5 for A. aegypti and 9.4 for A. albopictus. The fragments of 192 bp and 152 bp related to DENV-3, obtained from pools 34 and 49, was registered in GenBank with the access codes HM130699 and JF261696, respectively.

Conclusions: This study recorded the first natural evidence of the vertical transmission of the dengue virus in populations of A. aegypti and A. albopictus collected in Fortaleza, Ceará State, Brazil, opening a discuss on the epidemiological significance of this mechanism of viral transmission in the local scenario, particularly with respect to the maintenance of these viruses in nature during interepidemic periods.

Figure 1. Neighborhoods of Fortaleza where collections of Aedes spp were carried out.

DENV was isolated from Aedes mosquitoes in the neighborhoods colored in blue.

Figure 2. Indirect fluorescent antibody test of Aedes mosquitoes pools.

Pools 34 (A), 35 (B) and 49 (C) were positive for DENV; NC = negative control.

Figure 3. Electrophoresis in agarose gel of the products of RT-PCR.

Wells 1, 2 and 3 indicate negative pools for the dengue virus; well 4 reveals genomic fragment of DENV -3, obtained from the pool 34; well 5 reveals genomic fragment of DENV-2 obtained from the pool 35; well 6 reveals simultaneously genomic fragments of DENV-2 and DENV-3, obtained from the pool 49; well 7 contains the negative control, and well 8 contains a mix of DENV-1, DENV-2 and DENV-3 (positive control).