West Nile Virus Infection in Mosquitoes in the Mid-South USA, 2002–2005

Abstract

West Nile virus (family Flaviviridae, genus Flavivirus, WNV) was first detected in the Tennessee Valley and in Alabama in August 2001. In summer 2002, intensive viral activity was seen, but in subsequent years, viral activity settled into an enzootic pattern. Here, we report an analysis of viral activity in the mosquito fauna in the Mid-South from 2002 (the first year viral activity was detected in mosquitoes) through 2005. Eight mosquito species were infected with WNV during 2002. However, viral activity was only detected in four species--Culex salinarius Coquillett, Culex erraticus Dyar & Knab, Coquillettidia perturbans Walker, and Aedes vexans Meigen--in multiple years. The greatest number of positive pools was in Cx. erraticus and Cx. salinarius. Despite being specifically targeted for collection, Aedes albopictus Skuse was only found to be infected during the epiornitic year (2002), suggesting that under enzootic transmission conditions its role as a bridge vector in the region may not be significant. Virus-positive pools of Cx. erraticus were identified from winter-resting and early season dry ice-baited trap collections in 2005, implicating this species in WNV overwintering in Alabama. Molecular analysis of individuals initially identified as members of the Culex pipiens L. complex suggested that alleles characteristic of Cx. pipiens predominated in mosquitoes collected in Huntsville, AL, whereas alleles in the Auburn, AL, population were predominately characteristic of Culex quinquefaciatus Say. The southern boundary of the overlap zone of the two species seems to be located primarily between Huntsville and Auburn, a distance of 350 km.

Competency of Reptiles and Amphibians for Eastern Equine Encephalitis Virus

“…erraticus has been shown to feed upon reptiles at the TNF site. This is the most common species found at the TNF site and throughout the Southeastern United States 21,[28][29][30] and it is believed to represent a major potential vector of EEEV in this region. 21,28 It is therefore possible that any or all of these four mosquito species might be responsible for initiating the enzootic transmission cycle through feeding upon EEEV-infected snakes exiting hibernation in the spring.…”

Host Choice and West Nile Virus Infection Rates in Blood-Fed Mosquitoes, Including Members of theCulex pipiensComplex, from Memphis and Shelby County, Tennessee, 2002–2003

“…quadrimaculatus in Memphis, while Cx. salinarius has been implicated as a potential bridge vector in Connecticut (Andreadis et al 2004) and has been found to be frequently infected with WNV in studies conducted in the Southeastern United States (Godsey et al 2001, 2005, Cupp et al 2007). …”

West Nile Virus: Biology, Transmission, and Human Infection

“…There is evidence that C. pipiens in the eastern United States may feed on mammals and humans instead of birds during the late summer and early fall, and this "host switching" has also been reported with C. tarsalis in the western United States (96,212). There are several reports of WNV in Aedes mosquitoes, though they are not considered a primary vector in nature (46,58,83,184,216,221). WNV has also been detected in field-collected male A. triseriatus and C. salinarius (219), which not only points to vertical transmission of virus, as only females feed on animal blood, but also further supports that WNV has the ability to infect Aedes mosquitoes in nature.…”