What You Should Know About West Nile Virus
Updated September 2006
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 are
transmitted by blood-feeding insects such as mosquitoes. Most
infections with West Nile virus have been identified in wild birds,
horses and humans, but the virus can also infect various other wild and
domestic animals.
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 other parts of 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. The virus has been reported in
nearly all states.
Q: How is West Nile virus transmitted?
A:
Mosquitoes draw the virus from infected birds and transmit it to other
animals, including humans, through bites. West Nile viral encephalitis
develops when the virus multiplies and crosses the blood-brain barrier.
West Nile virus is not transmitted directly from animal to person,
person to animal, animal to animal or person to person; however, rare
instances of transmission via organ transplantation, blood transfusion,
transplacental infection, and breastfeeding have been reported. Cats
have been infected experimentally by eating WNV-infected mice. Ticks
infected with the virus have been found in Asia and Africa, but there
are no verified reports of ticks spreading the virus and their role in
transmission has not been determined.
Q: What is the risk of a person contracting West Nile virus?
A:
The risk of becoming ill from a single mosquito bite is extremely low.
In areas where mosquitoes carry the virus, less than 1% of mosquitoes
are actually infected. Even if mosquitoes are infected, less than 1% of
people bitten and infected by those mosquitoes become severely ill.
Q: What clinical signs are associated with West Nile virus infection?
A:
Humans—Most humans infected with the virus are not aware that
they have contracted it. If a person does become ill, clinical signs
are usually mild and include fever, headache, body aches and, in some
cases, skin rash and swollen lymph nodes. Signs of more severe
infection 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.
Horses—Horses that develop clinical West Nile virus infection
may exhibit incoordination, stumbling, weakness, muscle twitching,
depression, or fearfulness. A fever is not commonly observed. Severe
cases may become recumbent. The death rate in horses in approximately
30%, and is highest in recumbent horses. The number of cases of equine
WNV has decreased annually since 2002, and may be due to vaccination
and/or increased development of naturally acquired immunity.
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. 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 with the
virus, many members of these latter species rarely 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 tests.
As for most viral diseases, treatment consists of supportive care
(e.g., hospitalization, intravenous fluids, respiratory support,
anti-inflammatory therapy, prevention of secondary infections, and good
nursing care) while the affected animal's immune system responds to the
infection.
Q: Can West Nile viral encephalitis be prevented?
A: Several
vaccines are approved for use in horses to aid in the prevention of
viremia and clinical disease from West Nile virus infection. Many fly
repellent products also repel mosquitoes when used according to label
directions.
For other species, including humans, 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:
- Maintain the integrity of screens around your home, porch, and patio.
- During warm months, avoid outdoor activities at dusk and dawn when mosquito activity is at its peak.
- If you must be outdoors during hours when mosquitoes are most
active, cover up with shoes, socks, long pants and long-sleeved shirts.
- Use mosquito repellent on exposed skin and spray clothing with
repellents containing permethrin or DEET (N,N-diethyl-meta-toluamide).
When using insecticides or insect repellents, be sure to read and
follow the manufacturer's directions for use. Products containing DEET
should not be sprayed on dogs or cats. Consult your veterinarian about
the best ways to protect your pet from exposure.
- Eliminate standing water from any receptacles in which mosquitoes
might breed. For standing water than cannot be eliminated (e.g. bird
baths, etc.), consider the use of larvicides according to label
directions.
West Nile viral encephalitis is an emerging disease and new
information continues to become available. Additional information is
availabe from the following sources:
American Veterinary Medical Association
(www.avma.org)
U.S. Centers for Disease Control
(http://www.cdc.gov/ncidod/dvbid/westnile/index.htm)
U.S. Department of Agriculture's Animal and Plant Health Inspection Service
(http://www.aphis.usda.gov/vs/nahss/equine/wnv/index.htm)
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This information has been prepared as a service by the American Veterinary Medical Association.
Article Source: http://www.mydogplace.com/dog-content/dog-health-series/west-nile-virus-and-your-dog-article.html
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