Hamerlinck, G. | Search bioRxiv

bioRxiv2020

No evidence for insecticide resistance in a homogenous population of Aedes albopictus in Mecklenburg County, North Carolina

Aedes albopictus is a cosmopolitan mosquito species capable of transmitting arboviral diseases such as dengue, chikungunya, and Zika. To control this and similar species, public and private entities often rely on pyrethroid insecticides. Insecticide resistance status and physiological traits, such as body size, may contribute to local patterns of abundance, which is important for planning vector control. In this study, we genetically screened Ae. albopictus collected from June to August, 2017, in Mecklenburg County, North Carolina, for mutations conferring pyrethroid resistance, and examined spatiotemporal patterns of specimen size, as measured by wing length. We hypothesized that size variation would be associated with factors found to influence abundance in similar populations of Ae. albopictus, and could therefore serve as a proxy measure. The genetic screening results indicated that known pyrethroid resistance alleles in two kdr regions are not present in this population. We detected no significant associations between wing length and socioeconomic and landscape factors, but mosquitoes collected in June had significantly longer wing length than in July or August. The lack of resistance indicators suggest that this population has not developed insecticide resistance via voltage-gated sodium channel mutations. The greater wing lengths in June are likely driven by meteorological patterns, suggesting that short-term weather cues may modulate morphological characteristics that, in turn, affect local fecundity and virus transmission potential.

ecology↗

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↗