Lineage II of Southeast Asian/American DENV-2 is associated with a severe dengue outbreak in the Peruvian Amazon

Abstract

During 2010 and 2011, the Loreto region of Peru experienced a dengue outbreak of unprecedented magnitude and severity for the region. This outbreak coincided with the reappearance of dengue virus-2 (DENV-2) in Loreto after almost 8 years. Whole-genome sequence indicated that DENV-2 from the outbreak belonged to lineage II of the southeast Asian/American genotype and was most closely related to viruses circulating in Brazil during 2007 and 2008, whereas DENV-2 previously circulating in Loreto grouped with lineage I (DENV-2 strains circulating in South America since 1990). One amino acid substitution (NS5 A811V) in the 2010 and 2011 isolates resulted from positive selection. However, the 2010 and 2011 DENV-2 did not replicate to higher titers in monocyte-derived dendritic cells and did not infect or disseminate in a higher proportion of Aedes aegypti than DENV-2 isolates previously circulating in Loreto. These results suggest that factors other than enhanced viral replication played a role in the severity of this outbreak.

Figure 1.

MCC tree of DENV-2 southeast Asian/American genotype. The 95% highest posterior density (HPD) values of divergence time are shown by the node bar. Divergence events that led to the Peruvian lineages are specifically labeled with numbers of amino acid substitutions (above the branches) and 95% HPD of divergence year (below branches). BZ = Belize; JM = Jamaica; KH = Cambodia; KN = Saint Kitts and Nevis; MX = Mexico; NI = Nicaragua; PR = Puerto Rico; TH = Thailand; VI = Virgin Islands; VN = Vietnam.

Figure 2.

Comparative replication curves of lineages I and II DENV-2 strains in vitro. (A and B) Mean virus output of lineage I (triangles) and lineage II (squares) DENV-2 strains in mosquito epithelial (C6/36) and human hepatoma (Huh-7) cell lines; means ± SEs derived from four lineage I (FMD2303, NFI52, FSL699, and FMD1337) and seven lineage II (NFI1159, IQA2042, FPI00154, FPI00174, FPY00016, FSL4862, and IDA1081) DENV-2 strains are shown. (C and D) Daily virus output from days 0–6 after infection at an MOI of 0.01 by lineage I (FMD2303, NFI52, FSL699, and FMD1337) and lineage II (NFI1159, IQA2042, FPI00154, FPI00174, FPY00016, FSL4862, and IDA1081) DENV-2 strains in C6/36 and Huh-7 cell lines.

Figure 3.

Comparative replication curves of lineages I and II DENV-2 strains ex vivo. (A and B) Mean virus output of lineage I (black columns) and lineage II (white columns) DENV-2 strains in mo-DCs from two healthy human donors at 48 hours post-infection; means ± SEs derived from four lineage I and seven lineage II DENV-2 strains are shown. (C) Combined mean virus output of lineage I (solid columns) and lineage II (open columns) DENV-2 strains in mo-DCs from both donors (data from two individual experiments pooled together) at 48 hours post-infection. The limit of detection of the assay is 0.9 log10 FFUs/mL (solid line). Although the statistical analysis of viral replication in these cells included days 0–2 post-infection, to allow clear visualization of both donors and all virus isolates, only titers on day 2 post-infection are shown.