Aedes aegypti is the principal vector for dengue virus, of which there are four serotypes. No effective vaccine exists to protect against dengue infection, and in recent years investigators have begun to focus on the vector to elucidate factors contributing to the vectorial capacity of Ae. aegypti for dengue. The current study focuses specifically on the role temperature stress plays in stress protein expression and dengue vectorial capacity.
Three laboratory strains differing in their innate susceptibilities to dengue virus were subjected to a control or heat shock treatment during their late juvenile stages. At six time points post-heat shock, larvae from each strain and treatment group were randomly sampled to quantify levels of HSP70 expression and measure the differences among them. Moyo S, which is has the greatest innate dengue susceptibility, was also found to express significantly more HSP70 over time (p < 0.01). Expression was highest at 24 and 48 hours post-heat shock relative to all other time points (p < 0.05). Additionally, HSP70 expression was assessed in larvae collected from Trinidad, a nation plagued with endemic dengue transmission, in order to compare their stress protein profiles with those observed among the laboratory strains.
Adults from all six strain and treatment groups were challenged with a dengue infection at 3-5 days post-eclosion, and dengue dissemination was assayed over three time points post-infection from a total of 233 mosquitoes. RNA was extracted from one leg per individual and RT-PCR was performed to gauge the dengue infection status. The extrinsic incubation period was not found to influence the probability of occurrence of a disseminated infection in any significant way (p > 0.1 for all strain and treatment groups). There were, however, significant differences depending on the strain and treatment combination (p < 0.005). For each group, 90% confidence intervals were calculated; only the heat shocked Moyo S and control Trinidad groups had significant differences in their probabilities of infection.
The results of this study indicate that a great deal remains unknown about the factors that contribute to the vectorial capacity of Ae. aegypti to dengue. Evidence suggests a correlation between the level of stress protein expression and the degree of susceptibility of Ae. aegypti to dengue, but the strength of this relationship is not well defined. It is also not clear whether natural climate variation alters HSP70 expression in the field, and whether this variation might impact vectorial capacity in the adult mosquito. Exploring this phenomenon may elucidate a critical target for vector control in the future.