Under-the-Radar Dengue Virus Infections in Natural Populations of Aedes aegypti Mosquitoes

Abstract

The incidence of locally acquired dengue infections increased during the last decade in the United States, compelling a sustained research effort concerning the dengue mosquito vector, Aedes aegypti, and its microbiome, which has been shown to influence virus transmission success. We examined the "metavirome" of four populations of Aedes aegypti mosquitoes collected in 2016 to 2017 in Manatee County, FL. Unexpectedly, we discovered that dengue virus serotype 4 (DENV4) was circulating in these mosquito populations, representing the first documented case of such a phenomenon in the absence of a local DENV4 human case in this county over a 2-year period. We confirmed that all of the mosquito populations carried the same DENV4 strain, assembled its full genome, validated infection orthogonally by reverse transcriptase PCR, traced the virus origin, estimated the time period of its introduction to the Caribbean region, and explored the viral genetic signatures and mosquito-specific virome associations that potentially mediated DENV4 persistence in mosquitoes. We discuss the significance of prolonged maintenance of the DENV4 infections in A. aegypti that occurred in the absence of a DENV4 human index case in Manatee County with respect to the inability of current surveillance paradigms to detect mosquito vector infections prior to a potential local outbreak. IMPORTANCE Since 1999, dengue outbreaks in the continental United States involving local transmission have occurred only episodically and only in Florida and Texas. In Florida, these episodes appear to be coincident with increased introductions of dengue virus into the region through human travel and migration from countries where the disease is endemic. To date, the U.S. public health response to dengue outbreaks has been largely reactive, and implementation of comprehensive arbovirus surveillance in advance of predictable transmission seasons, which would enable proactive preventative efforts, remains unsupported. The significance of our finding is that it is the first documented report of DENV4 transmission to and maintenance within a local mosquito vector population in the continental United States in the ab-

Transmission potential of FloridianAedes aegyptimosquitoes for dengue virus serotype 4: Implications for estimating local dengue risk

“…Pairing previous evidence of DENV-4 circulating in local Ae. aegypti populations [17] with our transmission potential data, we believe FL to be at-risk for local transmission of DENV-4, and that there are likely undetected pockets of DENV-4 maintenance throughout the state. Clearly, future studies measuring vector competence should consider investigating if similar trends also exist between other laboratory and fields strains of all DENV serotypes, especially if the goal is to accurately determine transmission risk of an arbovirus in a given setting.…”

“…DENV-4H and DENV-4L share 93% nucleotide identity and 98% amino acid identity but the DENV-4H sequence has a notable 15-bp deletion in its 3' untranslated region (similar to other DENV-4 genotype IIb strains that have spread globally) [17]. Minor genetic differences alone between these strains may have an impact on vector competence, as seen previously with CHIKV [33] and DENV [34].…”

“…It was crucial to determine the transmission potential of a FL field-derived Ae. aegypti population for DENV-4 to understand the risk posed to human health and gain insights into how this virus could become established in mosquito populations in the absence of reported human cases [17]. Importantly, we ruled out the contribution of CFAV infection, a potential confounder in vector competence studies, as neither of these tested mosquito strains had an active CFAV infection.…”

“…We reported the first instance of DENV-4 detection in recent history in Manatee County FL Ae. aegypti, and this was in the absence of any reported FL human index cases for this serotype, which could be pointing to virus maintenance in the mosquito population through vertical transmission [17]. The genome of this Manatee Co. DENV-4 strain has high nucleotide and amino acid sequence identity (>99%) with a strain isolated from Haiti in 2014, raising questions about the competence of FL Ae.…”

Ecology and transmission of a dengue virus serotype 4 identified in wild Aedes aegypti in Florida

“…Gaining retrospective insight into arbovirus transmission dynamics and disease risk in a local setting is especially important considering that the original DENV-4M virus was detected from Ae. aegypti collected from a tourist corridor in Manatee County across two consecutive years and in the absence of DENV-4 human index cases (Boyles et al, 2020;Mosquito-Borne Disease Surveillance | Florida Department of Health).…”