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Sources of information about West Nile Virus in Pets for Clients at Foothills Animal Hospital

(Note that the concern for Dogs and Cats is apparently very low). Provided below are three sources of information that may be important for our clients and patients. In general we are following two main principles:

Center For Disease Control Information on West Nile Virus

Vertebrate Ecology

Transmission Cycle: 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 of at least 110 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. Nonetheless, disease from WN virus infection in dogs has yet to be documented.

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.

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.

 

From the New York City Dept. of health:

Q: Can West Nile virus cause illness in dogs or cats?
A: West Nile virus was isolated from one cat in New Jersey in 1999 and two cats in upstate New York in 2000. All were severely ill and died. A study in Queens in 1999 showed that from 5% to 11% of dogs tested had been exposed to West Nile virus, though none was clinically ill. It is important to remember that pets with neurologic disease should be first evaluated for other, more likely, causes of illness, including rabies.

Q: Can infected dogs or cats be carriers and transmitters of West Nile virus to humans?
A: West Nile virus is transmitted by infectious mosquitoes. There is no evidence that any mammals, including humans, dogs, and cats, can transmit West Nile virus. Veterinarians should take normal infection control precautions when caring for an animal suspected of having West Nile or any other viral infection.

Q: How do dogs or cats become infected with West Nile virus?
A: Dogs and cats become infected the same way humans become infected: by the bite of an infected mosquito.

Q: Can a dog or cat infected with West Nile virus infect other dogs or cats?
A: No. There is no documented evidence that West Nile virus is transmitted between dogs and cats.

Q: How long can a dog or cat be infected with West Nile virus?
A: The answer is not known at this time.

Q: What should I do if I think my dog, cat, or other pet might have West Nile virus?
A: While dogs and cats do not appear to suffer clinical illness from West Nile virus, if you think your pet is ill you should see your veterinarian promptly. Pets can develop neurologic diseases from many other causes, and these should be ruled out before testing for West Nile virus is considered. Veterinarians should contact the New York City or New York State Departments of Health to arrange for testing of pets suspected of having West Nile virus infection.

Q: Should a dog or cat infected with West Nile virus be euthanized?
A: No. As animals infected with West Nile do not transmit the virus to people or other animals, there is no reason to euthanize an infected animal. Treatment would be supportive and consistent with standard veterinary practices for animals infected with any viral agent.

For more information about West Nile virus, call the New York City Department of Health and Mental Hygiene West Nile Information Line, 24 hours a day, seven days a week, at 1-877-WNV-4NYC (1-877-968-4692); TTY/TDD (212) 442-7772 Mon.-Fri. During business hours; or check our Web site at nyc.gov/health.

 

From the American Veterinary Medical Association

Q: What is West Nile virus?
A: West Nile virus is an arbovirus (short for arthropod-borne virus) that causes encephalitis (inflammation of the brain). Arboviruses, including West Nile virus, are transmitted by blood-feeding insects such as mosquitoes. Most infections with West Nile virus have been identified in wild birds, but the virus can also infect humans, horses, dogs, cats, bats, chipmunks, skunks, squirrels, domestic rabbits, and domestic birds.

Q: Where did West Nile virus come from?
A: West Nile virus was first identified in the West Nile district of Uganda in 1937, and has since been found in Africa, Eastern Europe, West Asia, the Middle East, and the United States. The strain of virus found in the United States most closely resembles that found in the Mediterranean and Middle East.

Q: How is West Nile virus transmitted?
A: Mosquitoes draw the virus from infected birds and transmit it to animals and humans through bites. West Nile viral encephalitis develops in animals and humans when the virus multiplies and crosses the blood-brain barrier. West Nile virus is not transmitted directly from person to person, animal to person, person to animal, or animal to animal. Ticks infected with the virus have been found in Asia and Africa; however, there are no verified reports of ticks spreading the virus and their role in transmission has not been determined.

Q: What's the risk of becoming ill from West Nile virus?
A: In areas where mosquitoes carry the virus, less than 1% are actually infected. Even if mosquitoes are infected, less than 1% of people bitten and infected by those mosquitoes become severely ill. The risk of becoming ill from a single mosquito bite is extremely low.

Q: What clinical signs are associated with West Nile virus infection?
A: Horses—The most common sign is weakness, usually in the hindquarters. Weakness may be indicated by a widened stance, stumbling, leaning to one side, and toe dragging. In extreme cases, paralysis may follow. Fever is sometimes evident, as are depression and fearfulness. Approximately 40% of cases of West Nile viral encephalitis in horses proved fatal during the 1999 outbreak.

Humans—Most infections in humans are relatively mild, with flu-like symptoms including fever, headache, body aches and, in some cases, skin rash and swollen lymph glands. Signs of more severe infections include high fever, neck stiffness, muscle weakness, convulsions and paralysis. Death rates associated with severe infection range from 3% to 15% and are highest among the elderly.

Other animals—Wild birds infected with West Nile virus in the United States are most often found dead; therefore, descriptions of clinical signs in wild birds are not readily available. Nor have clinical signs associated with West Nile virus infection in dogs, cats, bats, chipmunks, skunks, squirrels, domestic rabbits, and domestic birds been well described. It appears that, although they may be infected, many of these latter species may not develop clinical signs of disease.

Q: How is West Nile viral encephalitis diagnosed and treated?
A: Diagnosis of West Nile viral encephalitis is based on a history of exposure, clinical signs, and results of diagnostic blood tests.

As for all viral diseases, treatment consists of providing support (e.g., hospitalization, intravenous fluids, respiratory support, prevention of secondary infections, and good nursing care) while the affected individual's immune system responds to the infection.

Q: Can West Nile viral encephalitis be prevented?
A: A vaccine is now available for horses. For other species, limiting exposure to mosquitoes is considered effective prevention.

The following actions may reduce the risk of mosquito bites and possible exposure to West Nile virus:

 

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