Differential Susceptibility of Two Field <i>Aedes aegypti</i> Populations to a Low Infectious Dose of Dengue Virus

<div><p>Background</p><p>The infectious dose required to infect mosquito vectors when they take a blood meal from a viremic person is a critical parameter underlying the probability of dengue virus (DENV) transmission. Because experimental vector competence studies typically examine the proportion of mosquitoes that become infected at intermediate or high DENV infectious doses in the blood meal, the minimum blood meal titer required to infect mosquitoes is poorly documented. Understanding the factors influencing the lower infectiousness threshold is epidemiologically significant because it determines the transmission potential of humans with a low DENV viremia, possibly including inapparent infections, and during the onset and resolution of the viremic period of acutely infected individuals.</p><p>Methodology/Principal Findings</p><p>We compared the susceptibility of two field-derived <i>Aedes aegypti</i> populations from Kamphaeng Phet, Thailand when they were orally exposed to low titers of six DENV-2 isolates derived from the serum of naturally infected humans living in the same region. The infectious dose, time-point post-blood feeding, viral isolate and mosquito population, were significant predictors of the proportion of mosquitoes that became infected. Importantly, the dose-response profile differed significantly between the two <i>Ae. aegypti</i> populations. Although both mosquito populations had a similar 50% oral infectious dose (OID₅₀), the slope of the dose-response was shallower in one population, resulting in a markedly higher susceptibility at low blood meal titers.</p><p>Conclusions/Significance</p><p>Our results indicate that mosquitoes in nature vary in their infectious dose-response to DENV. Thus, different mosquito populations have a differential ability to acquire DENV infection at low viremia levels. Future studies on human-to-mosquito DENV transmission should not be limited to OID₅₀ values, but rather they should be expanded to account for the shape of the dose-response profile across a range of virus titers.</p>