POSTED: August 30, 2004
To answer some excellent questions about the species of mosquitoes that transmit WNV, we have been doing some research....
In general, the research on WNV vectors is a quickly evolving field. The more species of biting insects (mosquitoes, midges and flies) they test for WNV infectivity, the more species they find that have the POTENTIAL to transmit the virus. In the area around NE Wyoming they have found that a midge (Culicoides sonorensis) can transmit WNV to sage grouse. In general, the primary mosquito for the Western U.S. to transmit WNV is a primarily avian mosquito (Culex tarsalis). Interestingly, in Wyoming the midge was about twice as susceptible for carrying WNV (22.2% positive) but was only 1/4 as infectious as the mosquito (infection rate 2.31 per 1000).
Under laboratory conditions, researchers found that all 10 species of mosquitoes found in California could be infected with WNV, and thus are POSSIBLE vectors. But, once again it was the primarily avian mosquito (Culex tarsalis) that had the highest infection rate. A "must read" paper for horse owners is this same crossover vector (Culex tarsalis) that also transmits Western equine encephalomyelitis virus (and other viral diseases).
Please find below some excerpts from a paper you can read in it's entirety on the internet.
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Vector Competence of California Mosquitoes for West Nile virus
Laura B. Goddard,* Amy E. Roth,* William
K. Reisen,* and Thomas W. Scott*
*University of California, Davis, California, USA
Suggested citation for this article: Goddard LB, Roth AE, Reisen WK, Scott TW. Vector competence of California mosquitoes for West Nile virus. Emerg Infect Dis [serial online] 2002 Dec [date cited];8. Available from: URL: http://www.cdc.gov/ncidod/EID/vol8no12/02-0536.htm#21
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ABSTRACT: To identify the mosquito species competent for West Nile virus (WNV) transmission, we evaluated 10 California species that are known vectors of other arboviruses or major pests: Culex tarsalis, Cx. pipiens pipiens, Cx. p. quinquefasciatus, Cx. stigmatosoma, Cx. erythrothorax, Ochlerotatus dorsalis, Oc. melanimon, Oc. sierrensis, Aedes vexans, and Culiseta inornata. All 10 became infected and were able to transmit WNV at some level. Ochlerotatus, Culiseta, and Aedes were low to moderately efficient vectors. They feed primarily on mammals and could play a secondary role in transmission. Oc. sierrensis, a major pest species, and Cx. p. quinquefasciatus from southern California were the least efficient laboratory vectors. Cx. tarsalis, Cx. stigmatosoma, Cx. erythrothorax, and other populations of Cx. pipiens complex were the most efficient laboratory vectors. Culex species are likely to play the primary role in the enzootic maintenance and transmission of WNV in California.
EXCERPTS:
In the western United States, SLEV (Saint Louis encephalitis virus (SLEV), and Western equine encephalomyelitis virus) WEEV share a common mosquito host, Cx. tarsalis, which will presumably also support WNV transmission.
DISCUSSION
Cx. tarsalis is one of the most efficient laboratory vectors of WNV tested from North America (10,13-15). This species is abundant in California and much of western North America, where it is involved in the maintenance and amplification of WEEV and SLEV (22). Considering its central role in the transmission of arboviruses in avian hosts and its susceptibility to WNV infection in the laboratory, Cx. tarsalis has the greatest potential of the species we studied to amplify and maintain WNV in California.
Mosquitoes in the Cx. pipiens species complex also may be an important enzootic mosquito host in California. Cx. p. pipiens was identified as a primary WNV vector during the 1999 New York outbreak (10) and has been suggested as a host for overwintering flaviviruses such as WNV and SLEV (35-38). This species could play a similar role in WNV transmission in California. Cx. p. pipiens is mainly ornithophilic (39), but Cx. p. quinquefasciatus feeds readily on mammals (25,40), potentially transferring WNV from birds to humans and horses.
Cx. stigmatosoma and Cx. erythrothorax are widely distributed species in California and were highly susceptible to WNV infection. Cx. stigmatosoma preferentially feeds on birds and may play a role as an enzootic vector. Conversely, Cx. erythrothorax behaves as an opportunistic feeder, potentially bridging WNV transmission between birds and mammals (25).
Lance & Dr. Jill Morrow, PhD
Biologist
