An Update on the Potential of North American Mosquitoes (Diptera: Culicidae) to Transmit West Nile Virus

Abstract

Since first discovered in the New York City area in 1999, West Nile virus (WNV) has become established over much of the continental United States and has been responsible for >10,000 cases of severe disease and 400 human fatalities, as well as thousands of fatal infections in horses. To develop appropriate surveillance and control strategies, the identification of which mosquito species are competent vectors and how various factors influence their ability to transmit this virus must be determined. Therefore, we evaluated numerous mosquito species for their ability to transmit WNV under laboratory conditions. This report contains data for several mosquito species not reported previously, as well as a summary of transmission data compiled from previously reported studies. Mosquitoes were allowed to feed on chickens infected with WNV isolated from a crow that died during the 1999 outbreak in New York City. These mosquitoes were tested approximately 2 wk later to determine infection, dissemination, and transmission rates. All Culex species tested were competent vectors in the laboratory and varied from highly efficient vectors (e.g., Culex tarsalis Coquillett) to moderately efficient ones (e.g., Culex nigripalpus Theobald). Nearly all of the Culex species tested could serve as efficient enzootic or amplifying vectors for WNV. Several container-breeding Aedes and Ochlerotatus species were highly efficient vectors under laboratory conditions, but because of their feeding preferences, would probably not be involved in the maintenance of WNV in nature. However, they would be potential bridge vectors between the avian-Culex cycle and mammalian hosts. In contrast, most of the surface pool-breeding Aedes and Ochlerotatus species tested were relatively inefficient vectors under laboratory conditions and would probably not play a significant role in transmitting WNV in nature. In determining the potential for a mosquito species to become involved in transmitting WNV, it is necessary to consider not only its laboratory vector competence but also its abundance, host-feeding preference, involvement with other viruses with similar transmission cycles, and whether WNV has been isolated from this species under natural conditions.

Migrating Birds as Dispersal Vehicles for West Nile Virus

“…First, the infected bird must fly to a new potential WNV transmission focus, where sufficient competent vectors (Turell et al, 2001(Turell et al, , 2005Apperson et al, 2002;Goddard et al, 2002) and amplifying hosts are present to support local WNV amplification. The successful introduction of WNV into a new amplification focus by a migrating bird is a stochastic process, for which probabilities are currently unknown.…”

Ecological correlates of risk and incidence of West Nile virus in the United States

“…This estimate of vector abundance was used in the statistical analyses described below. Species of mosquitoes that are likely to transmit WNV to humans in the St. Louis region are Aedes albopictus, members of the Culex pipiens complex, C. salinarius, C. restuans and C. tarsalis (Kilpatrick et al 2005;Tiawsirisup et al 2005;Turell et al 2005); these mosquito species were included as WNV vectors in our analysis. Oecologia (2009) 158:699-708 701 Due to the insufficient sample size of mosquitoes obtained at our study sites (very large numbers are required to accurately estimate infection prevalence), WNV infection prevalence in vector mosquitoes (i.e., proportion of mosquitoes infected with WNV) was obtained from the surveillance activities of local vector control agencies in similar habitat types near to our study sites (mean distance ± SD, 1.4 km ± 0.8).…”

“…Trap station criteria included at least three separate trapping events between 1st July and 15th September 2004 using gravid traps baited with hayinfused water. Mosquito infection prevalence data was restricted to Culex species because these are typically considered the most important WNV vectors (Turell et al 2005). WNV infection prevalence in mosquitoes was calculated using the ''Pooled Infection Rate Add-In'' in Excel provided by the CDC, which provides a bias-corrected maximum likelihood estimate of infection prevalence based on the number of mosquito pools, pool sizes, and number of positive pools (Biggerstaff 2003).…”

Host Feeding Patterns ofCulexMosquitoes and West Nile Virus Transmission, Northeastern United States

“…restuans , and Cx. salinarius have been implicated as the principal vectors because they are physiologically competent ( 5 ), frequently infected with the virus in nature, and closely associated with WNV transmission foci ( 6 ). However, the precise role that each of these species plays in enzootic transmission among birds or epidemic transmission to humans is not entirely clear.…”