Vertical transmission of Key West dengue-1 virus by Aedes aegypti and Aedes albopictus (Diptera: Culicidae) mosquitoes from Florida

Abstract

Following the 2009 and 2010 dengue-1 (DENV-1) outbreaks in Key West, FL, we used Florida Aedes aegypti (L.) mosquitoes and DENV-1 isolated from Key West in 2010 to test the hypothesis that if the 2009 and 2010 DENV-1 genome sequences are similar, then vertical transmission of DENV-1 from infected Ae. aegypti female mosquitoes to their eggs could have served as an interepidemic reservoir between outbreaks. We also investigated the ability of Florida Aedes albopictus (Skuse) mosquitoes to vertically transmit DENV-1. In addition, we determined the rates of infection and dissemination of these Florida mosquito species for DENV-1 and the effect of DENV-1 infection on oviposition success and number of mosquito eggs laid by females. Vertical transmission of DENV-1 was documented, with rates of 11.11% (2 out of 18) for Ae. albopictus and 8.33% (3 out of 36) for Ae. aegypti. Approximately 93% (111 out of 119) of Ae. aegypti that fed on DENV-1 in blood became infected, and 80% (89 out of 111) of infections were disseminated. Similarly, 93% of Ae. albopictus became infected (53 out of 57), and 85% (45 out of 53) of infections were disseminated. No significant differences were detected in numbers of eggs laid by either species after imbibing DENV-1 in blood, suggesting little cost of infection on number of eggs laid. Our results demonstrate that Florida Ae. aegypti and Ae. albopictus mosquitoes are competent vectors for DENV-1, whose maintenance between the 2009 and 2010 Key West outbreaks may have been facilitated by vertical transmission.

Fig. 1

The proportions of Ae. aegypti and Ae. albopictus mosquitoes in each infection category (uninfected, nondisseminated infection, or disseminated infection), after imbibing DENV-1-infected blood, which did not significantly differ (χ² = 0.66; df = 2; P = 0.72).

Fig. 2

Medians with 75 and 25 quartiles (±SE) for body titer of Ae. aegypti and Ae. albopictus mosquitoes with non-disseminated and disseminated infections. Different letters indicate significant differences determined by Wilcoxon two-sample tests with Bonferroni corrections (all P ≤ 0.0003).

Fig. 3

Relationship between body titer and number of eggs laid by infected Ae. aegypti and Ae. albopictus mosquitoes with detectable levels of DENV-1 RNA (crossing point ≤35). Spearman nonparametric correlations between fecundity, species, body titer, and infection category were statistically not significant (P ≥ 0.17), except for a negative relationship between the body titer of Ae. albopictus mosquitoes with nondisseminated infections and number of eggs laid (r =–0.76, P = 0.03).