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Updates on West Nile Virus in the USA

Updates on West Nile Virus in the USA

Animal Health One Health Public Health

According to the Southeastern Cooperative Wildlife Disease Study (SCWDS) in the College of Veterinary Medicine at the University of Georgia, West Nile virus (WNV) has spread rapidly since its introduction to the United States in 1999 and is now considered endemic throughout much of North America. WNV is a vector-borne flavivirus that is most commonly transmitted by mosquitoes in the Culex genus and circulates between mosquitoes, birds, and mammalian hosts (including humans). Numerous bird species can be infected with WNV but clinical outcome can vary significantly between species, ranging from inapparent infection to death. 

This varied clinical spectrum appears to occur between galliform species. For example, results from early WNV research indicate that some domesticated galliforms (e.g., chickens and domestic turkeys) are resistant to WNV-associated disease. In contrast, greater sage grouse (Centrocercus urophasianus) and more recently, ruffed grouse (Bonasa umbellus), are highly susceptible to WNV associated morbidity and mortality. The potential impacts of WNV on other upland game bird species such as wild turkey (Meleagris gallopavo silvestris) and bobwhite quail (Colinus virginianus) are largely unknown. 

M J Gilsdorf DVM

Therefore, SCWDS researchers have begun collaborating with wildlife biologists and veterinarians from multiple state agencies across the eastern United States as well as central and eastern Canada to test hunter-harvested, ruffed grouse blood samples for antibodies to WNV. These findings will ultimately be used to develop a multi-year, WNV antibody prevalence data set on ruffed grouse populations across part of their range in eastern North America. 

In response to similar concerns regarding, depressed population numbers and low recruitment rates in eastern wild turkey and northern bobwhite quail in some areas, SCWDS researchers are also exploring the potential impact of WNV on these species. During the summer and fall of 2019, eastern wild turkey poults and juvenile northern bobwhite quail will be experimentally infected with WNV and followed.

According to the Pennsylvania State Extension service, there is no evidence of animal-to-person or person-to-person transmission of West Nile virus. The only known way in which people can become infected is through the bite of an infected mosquito. However, even in areas where mosquitoes do carry the virus, very few mosquitoes are infected. Mosquitoes become infected after taking a blood meal from a wild bird carrying the virus in its bloodstream. Although some wild birds may harbor the virus, most species, with the exception of crows, do not become clinically ill. American crows, however, constitute a large proportion of the dead birds that have tested positive for the West Nile virus. Because the only means of preventing transmission of West Nile Virus is through mosquito control, mosquito control efforts are increased in any areas where West Nile virus is found to be present.

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