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Farm and Home Biosecurity
Consumer/General Public and Livestock/Row Crop Producer
West Nile Virus - More Information
West Nile encephalitis is an infection of the brain caused by West Nile
Virus. It is closely related to St. Louis encephalitis (SLE) virus found in the
United States. The virus has been found in Africa, western Asia, the Middle
East, the Mediterranean region of Europe, and most recently in the United States
(September of 1999).
The virus is transmitted by mosquitoes that acquire it from infected birds.
Humans and horses may be infected by the virus, but there is no documentation
that infected horses can spread the virus to uninfected horses or other animals.
Migrating birds may play a role in spreading the disease.
Studies have shown that normally only a small percentage of humans infected
with the virus will show symptoms of disease and even fewer will develop any
serious complications. The disease caused by West Nile Virus is very similar to
SLE, but is generally milder. There is no specific treatment, medication, or
cure for illnesses caused by West Nile Virus. However, the symptoms and
complications of the disease can be treated. Most people who get the illness
recover from it. There is no vaccine to protect humans against West Nile Virus
infection.
Horses infected with West Nile Virus can become sick and recover or possibly
die. It is likely that many horses become infected with the virus but recover
without showing any clinical signs of the disease. The U.S. Department of
Agriculture has approved a conditional license for a vaccine for horses against
West Nile Virus. The vaccine is available through your veterinarian. Boarding an
uninfected horse with an infected one will not lead to the other one becoming
infected. A mosquito that is not already carrying West Nile Virus cannot pick up
the virus by biting a horse or a human. The virus is not concentrated enough in
the blood of humans or horses to be spread this way. There is no reason to
destroy a horse just because it has been infected with West Nile Virus.
Treatment would be supportive and consistent with standard veterinary practices
for animals infected with a viral agent. There were 738 clinical cases of West
Nile Virus infection detected in horses from 20 States (January 1 to December
31, 2001). Mortality rate (death from the virus or euthanasia) was around 33% of
all those diagnosed as being infected with West Nile virus, in those horses for
which an outcome was reported.
Florida had the largest amount of horses infected with West Nile virus,
during the year 2001. The estimated economic impact on the state of Florida,
last year, was $250,000.
It is estimated that West Nile virus infection will spread further westward
during 2002, projected to reach the Rocky Mountains or further.
Through July 17, 2002 West Nile Virus has been confirmed in the following
states, with a listing of species affected: Alabama (birds), Arkansas (bird),
Connecticut (bird), Florida (birds & horses), Georgia (birds), Illinois
(birds), Indiana (bird), Kentucky (birds & horse), Louisiana (bird, horses
& three humans), Maryland (bird), Massachusetts (bird), Michigan
(birds), Nebraska (bird), New Jersey (birds), New York (birds), North Carolina
(bird), North Dakota (horse), Ohio (birds), Ontario, Canada (birds),
Pennsylvania (birds), Rhode Island (bird), Tennessee (birds), Texas (birds &
horses), Virginia (birds), Washington, DC (bird), and Wisconsin (bird).
West Nile virus has killed 18 people along the East Coast since it was first
detected in 1999. Last summer was the most severe, with 66 human infections and
9 deaths nationwide.
Arkansas had four birds test positive for West Nile virus, during 2001. Two
birds were in Union County, one in Saline County and one in Sebastian County. There
were NO confirmed cases of West Nile virus infection in Arkansas horses,
during 2001!
Because West Nile virus has been found in the state of Arkansas, it is
recommended that Arkansas horse owners consider having their horses vaccinated
for this disease. They need to discuss this issue with their local veterinarian.
Be mindful that the manufacturer’s recommendations include giving a second
dose 3-6 weeks after the initial dose, followed by a yearly booster. It has been
shown that one dose is not protective and that it may take several weeks after
the second dose has been administered for measurable antibody response to
appear. Therefore, if owners choose to vaccinate against West Nile Virus, it
would be best to vaccinate horses early in the spring, before the summer
mosquito activity increases.
To reduce the risk of human infection with West Nile Virus, one should:
- Stay indoors at dawn, dusk, and early evening.
- Wear long-sleeved shirts and long pants whenever you are outdoors.
- Spray clothing with repellents containing permethrin or DEET since
mosquitoes may bite through thin clothing.
- Apply insect repellent sparingly to exposed skin.
- Repellents may irritate the eyes and mouth, so avoid applying repellent
to the hands of children.
- Whenever you use an insecticide or insect repellent, be sure to read
and follow the manufacturer’s “Directions For Use”, as printed on the
product.
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