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Simple Summary: Aedes aegypti and Ae. albopictus mosquitoes are competent transmitters of Zika virus (ZIKV) and are widely distributed throughout the state of Florida. Investigations of the long-term maintenance of the virus that allows outbreaks to persist in adverse environmental conditions are limited. One mechanism for arboviral maintenance in nature is vertical transmission (VT) of a virus passed directly from parent to offspring during reproduction. This study assesses the potential of Florida Ae. aegypti and Ae. albopictus to vertically transmit ZIKV. To address this gap in our understanding of this critical risk parameter, we orally exposed Florida F3 generation Ae. aegypti and Ae. albopictus to ZIKV infected blood meals using a dose of ZIKV within the range of viremia levels experienced by infected humans. We observed low VT in both Ae. aegypti (1.1–3.2%) and Ae. albopictus (0–0.3%) mosquitoes; despite imbibing infected blood at titers that yielded high susceptibility to infection and modest horizontal transmission rates. Filial infection rates; testing individual mosquitoes; for Ae. aegypti and Ae. albopictus were 6–10% and 0–6.4%, respectively. Both invasive Stegomyia mosquitoes were capable of vertically transmitting ZIKV under laboratory conditions; and approximately 5% of female progeny of Ae. aegypti were capable of transmitting ZIKV upon first bite. The Zika virus pandemic of 2015, with mosquitoes Aedes aegypti and Ae. albopictus as the putative vectors, prompted public health concerns and the need to improve our understanding of both the horizontal and vertical transmission of Zika virus. Local transmission is especially concerning for Florida, where these two mosquito species are abundant and widespread throughout much of the year. Here, we evaluate the relative vertical transmission and filial infection rate of progeny of Florida Ae. aegypti and Ae. albopictus following ingestion of infected blood by parental mosquitoes at either 6 or 7 log10 plaque forming units/mL of Zika virus. Florida Ae. aegypti exhibited higher rates of disseminated infection than Ae. albopictus, consistent with other studies indicating greater permissibility of Zika virus in Ae. aegypti. We observed low vertical transmission in both Ae. aegypti (1.1–3.2%) and Ae. albopictus (0–0.3%) mosquitoes, despite imbibing infected blood at titers that yielded high susceptibility to infection and modest horizontal transmission rates. Filial infection rates, testing individual mosquitoes for Ae. aegypti and Ae. albopictus, were 6–10% and 0–6.4%, respectively. Both these invasive Stegomyia mosquitoes were capable of vertically transmitting Zika virus under laboratory conditions, and approximately 5% of female progeny of Ae. aegypti were capable of transmitting Zika virus upon first bite. [ABSTRACT FROM AUTHOR]

The Asian lineage of Zika virus (ZIKV), a mosquito-borne pathogen originally from Africa, caused an epidemic into Brazil in 2015 and subsequently spread throughout the Americas. Local transmission in the U.S. is a public health concern, especially for Florida where the mosquito vectors Aedes aegypti and Ae. albopictus are widespread, abundant, and there is a high potential for virus introduction due to imported cases. Here we evaluate relative susceptibility to infection and transmission of Zika virus among geographic populations of Ae. aegypti and Ae. albopictus in Florida. Both species have been implicated as ZIKV vectors elsewhere, but both virus and vector genotype are known to influence transmission capacities and, hence, the risk of outbreaks. We test the hypothesis that Ae. aegypti and Ae. albopictus show geographic differences in midgut and salivary gland barriers that limit ZIKV transmission, using local populations of the two vector species recently colonized from three regions of Florida to compare their susceptibility to ZIKV infection, disseminated infection, and transmission potential. Susceptibility to infection was higher in Ae. aegypti (range 76–92%) than Ae. albopictus (range 47–54%). Aedes aegypti exhibited 33–44% higher susceptibility to infection than Ae. albopictus, with Ae. aegypti from Okeechobee, FL having 17% higher susceptibility to infection than Ae. aegypti from Miami, FL. Similarly, disseminated infection was higher in Ae. aegypti (range 87–89%) than Ae. albopictus (range 31–39%), although did not vary by region. Enhanced infection and disseminated infection in Ae. aegypti were associated with higher viral loads in mosquito samples than in Ae. albopictus. Transmission rates did not vary by species or region (range 26–47%). The results support the hypothesis that Ae. aegypti, but not Ae. albopictus, exhibited regional differences in midgut infection barriers. Our observation of higher vector competence for Ae. aegypti than Ae. albopictus, together with this species greater propensity to feed on humans, lends support to the notion that Ae. aegypti is regarded as the primary vector for ZIKV and public health concern in continental U.S. [ABSTRACT FROM AUTHOR]

The Asian genotype of Zika virus (ZIKV) emerged in Brazil in 2015 and subsequently spread throughout the Americas. In July 2016, Florida experienced its first locally acquired ZIKV infection in the continental U.S. Concerns about health risks from ZIKV infection have increased the need to investigate the interactions between potential mosquito vectors and ZIKV. The time it takes for an arbovirus to propagate within a mosquito, and become transmissible, is the extrinsic incubation period (EIP). The EIP for potential mosquito vectors in Florida is unknown. To address this gap in the understanding of ZIKV epidemiology, Florida Aedes aegypti (L.) and Ae. albopictus (Skuse) were orally exposed to ZIKV infected blood meals and fully engorged mosquitoes were held at a constant temperature of 28 °C through the duration of the experiment. Saliva expectorates were collected from cohorts of mosquitoes and tested for the presence of ZIKV at three-day intervals over a period of 24 days to allow for an evaluation of the EIP of the emergent Asian lineage of ZIKV. High rates of infected bodies in Ae. albopictus (75–94%) and Ae. aegypti (68–86%) were observed throughout the incubation period, which did not differ by species. Higher rates of disseminated infection were observed later during the incubation period but did not differ between species. We calculated the 50% EIP to be shorter in Ae. albopictus than Ae. aegypti (16.2 and 18.2 days post infection, respectively). The competence for ZIKV observed in both species may contribute to high rates of ZIKV transmission in Florida populations. [ABSTRACT FROM AUTHOR]