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West Nile (WN) virus is amplified during periods of adult mosquito blood-feeding by continuous transmission between mosquito vectors and bird reservoir hosts. Infectious mosquitoes carry virus particles in their salivary glands and infect susceptible bird species during blood-meal feeding. Competent bird reservoirs will sustain an infectious viremia (virus circulating in the bloodstream) for 1 to 4 days after exposure, after which these hosts develop life-long immunity. A sufficient number of vectors must feed on an infectious host to ensure that some survive long enough to feed again on a susceptible reservoir host.

People, horses, and most other mammals are not known to develop infectious-level viremias very often, and thus are probably "dead-end" or incidental-hosts.

Birds

West Nile virus has been detected in dead birds in 138 species. Although birds, particularly crows and jays, infected with WN virus can die or become ill, most infected birds do survive. Click here for more information on species of dead birds in the U.S. in which West Nile virus has been detected.

There is no evidence that a person can get WN virus from handling live or dead infected birds. Persons should avoid bare-handed contact when handling any dead animals, and use gloves or double plastic bags to place the bird carcass in a garbage bag or contact their local health department for guidance.

Dogs and Cats

West Nile virus does not appear to cause extensive illness in dogs or cats. There is a single published report of WN virus isolated from a dog in southern Africa (Botswana) in 1982. West Nile virus was isolated from a single dead cat in 1999. A serosurvey in New York City of dogs in the 1999 epidemic area indicated that dogs are frequently infected. Update.

There is no documented evidence of person-to-person or animal-to-person transmission of WN virus. Because WN virus is transmitted by infectious mosquitoes, dogs or cats could be exposed to the virus in the same way humans become infected. Veterinarians should take normal infection control precautions when caring for an animal suspected to have this or any viral infection. It is possible that dogs and cats could become infected by eating dead infected animals such as birds, but this is undocumented. "Spot flea products are reportedly not effective at repelling or killing mosquitoes. However, flea sprays containing pyrethrins may have some value as repellants. Follow label directions carefully."¹

There is no reason to destroy an animal just because it has been infected with WN virus. Full recovery from the infection is likely. Treatment would be supportive and consistent with standard veterinary practices for animals infected with a viral agent.

Horses

Cases of WN virus disease in horses have been documented, either by virus isolation or by detection of WN virus-neutralizing antibodies in 1999, 2000, and 2001. Approximately 40% of equine WN virus cases results in the death of the horse. Horses most likely become infected with WN virus in the same way humans become infected, by the bite of infectious mosquitoes.

In locations where WN virus is circulating, horses should be protected from mosquito bites as much as possible. Horses vaccinated against eastern equine encephalitis (EEE), western equine encephalitis (WEE), and Venezuelan equine encephalitis (VEE) are NOT protected against WN virus infection. A West Nile virus vaccine for horses was recently licensed, but its effectiveness is unknown. Horses infected by WN virus develop a brief low-level viremia that is rarely, if ever, infectious to mosquitoes. There is no reason to destroy a horse just because it has been infected with WN virus. Data suggest that most horses recover from the infection. Treatment would be supportive and consistent with standard veterinary practices for animals infected with a viral agent.

Other Vertebrates

Through December 2001, CDC has also received a small number of reports of WN virus infection in bats, a chipmunk, a skunk, a squirrel, and a domestic rabbit.

CDC cannot guarantee that the identities of birds reported to its Arbonet surveillance reporting database are correct.

The following 138 bird species have been reported to CDC's West Nile Virus avian mortality database from 1999-present.

CDC cannot guarantee that the identities of birds reported to its Arbonet surveillance reporting database are correct.

Native Bird Species
American Crow American Goldfinch American Kestrel American Robin American Tree Sparrow American White Pelican Bald Eagle Baltimore Oriole Barn Swallow Barred Owl Belted Kingfisher Black Skimmer Black Vulture Black-billed Magpie Black-capped Chickadee Black-crowned Night Heron Blackpoll Warbler Black-throated Blue Warbler Black-whiskered Vireo Blue Jay Boat-tailed Grackle Brewer's Blackbird Broad-winged Hawk Brown Thrasher Brown-headed Cowbird Budgerigar Canada Goose Canada Warbler Canvasback Carolina Chickadee Carolina Wren Cedar Waxwing Chimney Swift	Common Grackle Common Ground-Dove Common Loon Common Nighthawk Common Raven Common Yellowthroat Cooper's Hawk Dickcissel Double-crested Cormorant Downy Woodpecker Eastern Bluebird Eastern Phoebe Eastern Screech-Owl Eurasian Wigeon European Starling Field Sparrow Fish Crow Great Blue Heron Great Horned Owl Green Heron Hermit Thrush Herring Gull Hooded Warbler Fox Sparrow Golden Eagle Gray Catbird Great Black-backed Gull Great Blue Heron Great Horned Owl Great-tailed Grackle Green Heron Harris' Hawk	Hermit Thrush Herring Gull Hooded Warbler House Finch House Sparrow Kentucky Warbler Killdeer Laughing Gull Least Bittern Loggerhead Shrike Mallard Merlin Mississippi Kite Mourning Dove Mute Swan Nashville Warbler Northern Bobwhite Northern Cardinal Northern Mockingbird Northern Parula Northern Saw-whet Owl Northern Waterthrush Osprey Ovenbird Purple Finch Purple Martin Red-headed Woodpecker Red-shouldered Hawk Red-tailed Hawk Red-winged Blackbird Ring-billed Gull Ring-necked Pheasant	Rock Dove Rough-legged Hawk Ruby-throated Hummingbird Ruddy Turnstone Ruffed Grouse Rusty Blackbird Sandhill Crane Savannah Sparrow Scarlet Ibis Sharp-shinned Hawk Short-eared Owl Snowy Owl Song Sparrow Steller's Jay Swainson's Hawk Swallow-tailed Kite Traill's Flycatcher Tufted Titmouse Turkey Vulture Veery Virginia Rail Warbling Vireo Western Scrub-Jay White-breasted Nuthatch White-crowned Pigeon Wild Turkey Wood Duck Wood Thrush Yellow Warbler Yellow-billed Sapsucker Yellow-billed Cuckoo Yellow-rumped Warbler

Exotic and Captive Species
Blythe's Tragopan Bronze-winged Duck Chilean Flamingo Cockatiel	Cockatoo Domestic Chicken Emu European Goldfinch	Guanay Cormorant Impeyan Pheasant Lorikeet species	Macaw Varied Tit Zebra Finch