Efficiency of dengue serotype 2 virus strains to infect and disseminate in Aedes aegypti

Abstract

Dengue serotype 2 (DEN-2) viruses with the potential to cause dengue hemorrhagic fever have been shown to belong to the Southeast (SE) Asian genotype. These viruses appear to be rapidly displacing the American genotype of DEN-2 in the Western Hemisphere. To determine whether distinct genotypes of DEN-2 virus are better adapted to mosquito transmission, we classified 15 viral strains of DEN-2 phylogenetically and compared their ability to infect and disseminate in different populations of Aedes aegypti mosquitoes. Envelope gene nucleotide sequence analysis confirmed that six strains belonged to the American genotype and nine strains were of the SE Asian genotype. The overall rate of disseminated infection in mosquitoes from Texas was 27% for the SE Asian genotype versus 9% for the American genotype. This pattern of infection was similar in another population of mosquitoes sampled from southern Mexico (30% versus 13%). Together, these findings suggest that Ae. aegypti tends to be more susceptible to infection by DEN-2 viruses of the SE Asian genotype than to those of the American genotype, and this may have epidemiologic implications.

Figure 1

Maximum likelihood tree depicting the phylogenetic relationships of 18 dengue serotype 2 viruses, based on nucleotides of the envelope gene (1,485 bases). Numbers on branches represent bootstrap support for each branch. Horizontal branch lengths are proportional to the percentage of divergence in the nucleotide sequence. Viruses are denoted by the first four letters of the country of origin, the last two digits of year of isolation, and the strain number. Sylvatic strains from Senegal, Guinea, and Côte d’Ivoire served as an outgroup.

Figure 2

Infection and dissemination of dengue serotype 2 viruses in the A, McAllen and B, Tehuantepec colonies of Aedes aegypti. Mosquitoes were scored as positive if dengue virus antigen was detected in the head tissues by an indirect fluorescent antibody test. American genotype viruses are depicted by white bars and Southeast (SE) Asian genotypes are depicted by black bars. Error bars show the standard deviation.