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West Nile Virus-Pet Concerns

West Nile Virus-Pet Concerns

Thanks to Dr.Branson W. Ritchie, D.V.M., PhD and Veterinary Learning Systems http://www.vetlearn.com

Life Cycle of the Virus-WestNile_cycle.gif

West Nile Virus (WNV) is one of the most widely distributed viruses. In Africa and Eurasia, free- range birds are the principal hosts of WNV, several species of mosquitoes serve as vectors, and humans and horses are considered incidental end hosts. Most birds are resistant to the encephalopathy that occurs in some infected horses and humans. A variant of the WNV has been occurring in the United States has an increased pathogenicity for birds.

WNV has now become endemic  the  USA and has cause seasonal outbreaks of disease in birds, horses, and humans. Transmission of WNV will depend on a high concentration of an effective mosquito vector. WNV infections in humans are usually mild, but may be fatal in immune compromised people.

Global warming and the resultant wet, humid weather have been suggested to increase the number of mosquitoes, resulting in more frequent and severe outbreaks of the disease.

WNV is suspected to survive over winter in hibernating mosquitoes, and transfer has been shown to occur through breeding of mosquitoes. It has been suggested that infected birds may serve to reintroduce the virus.

WNV to date has caused death in more than 20 species of birds (death in  raptors), including the American robin, bald eagle, black-billed magpie, black crowned night heron, blue jay, Blyth’s tragopan, broad- wing hawk, bronze-winged duck, Chilean flamingo, Cooper’s hawk, cormorant, crow, Impeyan pheasant, laughing gall, mallard, sandhill crane, snowy owl, red-tailed hawk, ring-billed gull, rock dove, and yellow-billed cuckoo. Several species of Psittaciformes-the ringed-neck parakeet and the vasa parrot, and cockatiel have also been shown to be susceptible to the WNV.  List of birds affected http://www.nwhc.usgs.gov/research/west_nile/wnvaffected.html

In addition WNV was confirmed as the cause of death (or nervous system signs requiring euthanasia) in horses in Long Island. Clinical signs include lethargy, loss of balance, hind limb paresis and paralysis, and convulsions.

Most mammals infected with WNV other than horses and lemurs, develop a low viremia of short duration and are not considered important in the maintenance of dissemination of this virus and one clinical case has been reported in dogs. Signs included twitching of the ears and face and disorientation.  Other types of encephalitis were ruled out.   Fortunately the dog recovered. At this time, it is felt that dogs are resistant to this virus and will recover from infection. Infection in cats have not been observed at this time.

Recurring seasonal outbreaks of WNV should be expected, particularly when above normal temperatures and precipitation favor proliferation of mosquitoes.

The health departments (Q & A Maryland Department of Health} are now implementing spraying with permethrin to kill the mosquitoes. Although, permethrin is toxic to cats, the concentration according to the health department is very low and is not a threat to cats.

Laboratories that Test for WNV

National Wildlife Health Center Biological Resources Division 6006 Schroeder Rd. Madison, Wi 53711

Phone 608 270 2400 fax 608 270 2415

National Veterinary Services Laboratory U.S.D.A. 1800 Dayton Ave. Ames, IA 50010 Phone 515 663 7266 fax 515 663 7397

 

 

 

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