Endemic Venezuelan equine encephalitis in northern Peru

Abstract

Since Venezuelan equine encephalitis virus (VEEV) was isolated in Peru in 1942, >70 isolates have been obtained from mosquitoes, humans, and sylvatic mammals primarily in the Amazon region. To investigate genetic relationships among the Peru VEEV isolates and between the Peru isolates and other VEEV strains, a fragment of the PE2 gene was amplified and analyzed by single-stranded conformation polymorphism. Representatives of seven genotypes underwent sequencing and phylogenetic analysis. The results identified four VEE complex lineages that cocirculate in the Amazon region: subtypes ID (Panama and Colombia/Venezuela genotypes), IIIC, and a new, proposed subtype IIID, which was isolated from a febrile human, mosquitoes, and spiny rats. Both ID lineages and the IIID subtype are associated with febrile human illness. Most of the subtype ID isolates belonged to the Panama genotype, but the Colombia/Venezuela genotype, which is phylogenetically related to epizootic strains, also continues to circulate in the Amazon basin.

Figure 1

Map of Peru showing the geographic distribution of the Venezuelan equine encephalitis virus (VEEV) complex isolates included in the study. Numbers in parenthesis indicate the number of isolates compared to the total number of febrile cases during the year. ID, IAB, IIIC, IIID correspond to VEEV subtypes isolated during the indicated year.

Figure 2

Map of Iquitos showing the locations of human Venezuelan equine encephalitis virus cases in the city.

Figure 3

Phylogenetic tree of the Venezuelan equine encephalitis virus (VEEV) complex derived from partial PE2 gene sequences of Peruvian VEEV isolates and homologous sequences published previously, using the neighbor joining program implemented in PAUP 4.0 (22). The tree was rooted using an outgroup comprised of four major lineages of Eastern Equine Encephalitis virus (26). Virus strains are labeled by VEE complex subtype, abbreviated country (FL=Florida, USA) and year of isolation, followed by strain designation. Numbers indicate bootstrap values for clades to the right.

Figure 4

Unrooted phylogenetic tree of the Venezuelan equine encephalitis virus (VEEV) complex and other representative alphaviruses derived from complete structural polyprotein sequences using the neighbor joining program implemented in PAUP 4.0 (22). Viruses are labeled by species according to the International Committee for Taxonomy of Viruses (27). VEEV subtype IIIC and IIID strain names are in parentheses. Numbers indicate bootstrap values for clades to the right.