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. 2016 Nov;29(11):2205-2218.
doi: 10.1111/jeb.12939. Epub 2016 Aug 8.

Rise and fall of vector infectivity during sequential strain displacements by mosquito-borne dengue virus

C C Andrade  1 , K I Young  2 , W L Johnson  2 , M E Villa  2 , C A Buraczyk  2 , W B Messer  3   4 , K A Hanley  2
Affiliations

Rise and fall of vector infectivity during sequential strain displacements by mosquito-borne dengue virus

C C Andrade et al. J Evol Biol. 2016 Nov.

Abstract

Each of the four serotypes of mosquito-borne dengue virus (DENV-1-4) comprises multiple, genetically distinct strains. Competitive displacement between strains within a serotype is a common feature of DENV epidemiology and can trigger outbreaks of dengue disease. We investigated the mechanisms underlying two sequential displacements by DENV-3 strains in Sri Lanka that each coincided with abrupt increases in dengue haemorrhagic fever (DHF) incidence. First, the post-DHF strain displaced the pre-DHF strain in the 1980s. We have previously shown that post-DHF is more infectious than pre-DHF for the major DENV vector, Aedes aegypti. Then, the ultra-DHF strain evolved in situ from post-DHF and displaced its ancestor in the 2000s. We predicted that ultra-DHF would be more infectious for Ae. aegypti than post-DHF but found that ultra-DHF infected a significantly lower percentage of mosquitoes than post-DHF. We therefore hypothesized that ultra-DHF had effected displacement by disseminating in Ae. aegypti more rapidly than post-DHF, but this was not borne out by a time course of mosquito infection. To elucidate the mechanisms that shape these virus-vector interactions, we tested the impact of RNA interference (RNAi), the principal mosquito defence against DENV, on replication of each of the three DENV strains. Replication of all strains was similar in mosquito cells with dysfunctional RNAi, but in cells with functional RNAi, replication of pre-DHF was significantly suppressed relative to the other two strains. Thus, differences in susceptibility to RNAi may account for the differences in mosquito infectivity between pre-DHF and post-DHF, but other mechanisms underlie the difference between post-DHF and ultra-DHF.

Keywords: Aedes; RNA interference; competitive displacement; dengue virus; mosquito; trade-off; vector.

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Figures

Figure 1
Figure 1
Isolates of the post-DHF DENV-3 strain (black, solid) infected a significantly higher percentage of Aedes aegypti mosquitoes than isolates of the ultra-DHF DENV-3 strain (red, hatched) 14 days after engorgement with bloodmeals containing designated dengue virus isolates. Sample size (N) is reported in parentheses below isolate name. See text for statistical analysis.
Figure 2
Figure 2
Mean percentage (plus or minus one standard error) of Aedes aegypti mosquitoes infected with (top panel) and generating a disseminated infection of (bottom panel) pre-DHF (blue squares), post-DHF (black circles), and ultra-DHF (red triangles) strains of DENV-3 at days 6, 10, and 14 after feeding on bloodmeals containing isolates of each strain. See text for statistical analysis.
Figure 3
Figure 3
Replication kinetics of pre-DHF (solid blue square, circle and upright triangle), post-DHF (solid black diamond, crossed lines, and inverted triangle), and ultra-DHF (open, red symbols) strains in C6/36 (top panel) and U4.4 (bottom panel) cells. Note that y-axes are at different scales to enhance clarity. See text for statistical analysis.
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