Yellow fever virus in Haemagogus leucocelaenus and Aedes serratus mosquitoes, southern Brazil, 2008

Abstract

Yellow fever virus (YFV) was isolated from Haemagogus leucocelaenus mosquitoes during an epizootic in 2001 in the Rio Grande do Sul State in southern Brazil. In October 2008, a yellow fever outbreak was reported there, with nonhuman primate deaths and human cases. This latter outbreak led to intensification of surveillance measures for early detection of YFV and support for vaccination programs. We report entomologic surveillance in 2 municipalities that recorded nonhuman primate deaths. Mosquitoes were collected at ground level, identified, and processed for virus isolation and molecular analyses. Eight YFV strains were isolated (7 from pools of Hg. leucocelaenus mosquitoes and another from Aedes serratus mosquitoes); 6 were sequenced, and they grouped in the YFV South American genotype I. The results confirmed the role of Hg. leucocelaenus mosquitoes as the main YFV vector in southern Brazil and suggest that Ae. serratus mosquitoes may have a potential role as a secondary vector.

Figure 1

Municipalities in Rio Grande do Sul State, southern Brazil, where mosquito specimens were collected during November 2008.

Figure 2

Phylogenetic analysis of partial (1,205 nt) structural region of the envelope gene of 6 yellow fever virus (YVF) isolates (boldface) sequenced from samples recovered from hematophagous arthopods collected in Rio Grande do Sul State, southern Brazil, November 2008. Comparison is shown with sequences of 17 genotype I YFV strains from Brazil and with sequences of 6 reference strains of genotype II from South America (Peru, Bolivia, and Brazil) obtained from GenBank. The analysis was performed by the neighbor-joining method; the nucleotide distance was calculated by the Kimura 2-parameter method. Bootstrap values were calculated after 1,000 replicates and are listed only in the main branches. The sequences of YFV strain Asibi and Uganda were used as outgroups. Scale bar indicates a divergence of 10%.