Mathias, D. K. | Search bioRxiv

bioRxiv2021

Intrinsic variation in the vertically transmitted insect-specific core virome of Aedes aegypti

Since 2009, local outbreaks of dengue (serotypes 1-3) mediated by Aedes aegypti mosquitoes have occurred in the United States, particularly in Florida (FL). In 2016 and 2017, dengue virus serotype 4 was found alongside several insect-specific viruses (ISVs) in pools of A. aegypti from sites in Manatee County, FL, in the absence of an index case. Although ISVs have been characterized in A. aegypti globally, the constitution of a core virome in natural populations remains unclear. Using mosquitoes sampled from the same area in 2018, we compared baseline ovary viromes of field (G0) and lab (Orlando) A. aegypti via metagenomic RNA sequencing. Across all samples, virome composition varied by sample type (field- or colony-derived). Four ISVs comprised >97% of virus sequences: a novel partiti-like virus (Partitiviridae), a previously described toti-like virus (Totiviridae), unclassified Riboviria, and four previously described orthomyxo-like viruses (Orthormyxoviridae). Whole or partial genomes for the toti-like virus, partiti-like virus, and one orthomyxo-like virus were assembled and analyzed phylogenetically. Multigenerational maintenance of these ISVs was confirmed orthogonally by RT-PCR in G0 and G7 mosquitoes, indicating vertical transmission as the mechanism for ISV sustentation. This study provides fundamental information regarding ISV ecology, persistence, and variation in A. aegypti in nature.

microbiology↗

bioRxiv2020

Under-the-radar dengue virus infections in natural populations of Aedes aegypti mosquitoes

The incidence of locally acquired dengue infections increased during the last decade in the United States, compelling a sustained research effort on 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 Ae. aegypti mosquitoes collected in 2016-2017 from Manatee County, Florida. 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 two-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, as well as 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 these DENV4 infections in Ae. 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. ImportanceSince 1999, dengue outbreaks in the continental United States (U.S.) involving local transmission have occurred 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 endemic countries. To date, the U.S. public health response to dengue outbreaks is 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 non-outbreak DENV4 transmission and maintenance within a local mosquito vector population in the continental U.S.in the absence of a human case during a two-year time period. Our data suggest that molecular surveillance of mosquito populations in high-risk, high tourism areas of the U.S., may allow for proactive, targeted vector control before potential arbovirus outbreaks.

ecology↗