West Nile virus (WNV) affects humans, birds,
horses, and other animals. The virus is carried from infected birds (the host
animal) to humans and other mammals through mosquito bites. When a mosquito
bites, a small amount of blood is injected into the skin of the bitten person
or animal. This infected blood can transmit WNV or other similar diseases.
West Nile virus is more commonly found in the eastern United States.
West Nile virus disease activity has spread rapidly since 1999, when it was
first reported in the United States. The main period of risk is from July
through September, but cases have occurred from May through December. The
outbreak of WNV infection in the United States during the summer of 2002 was
the largest reported. There were 284 deaths and 4156 human cases of WNV infection
reported in 2002. The July 23/30, 2003, issue of JAMA includes articles about WNV.
Loss of appetite
Nausea or vomiting
Confusion, delirium, or coma
Most people who become infected with WNV do not develop severe illness.
Mild WNV infections usually last 3 to 6 days after an incubation (delay) period
of 3 to 14 days after the initial exposure to the virus. Approximately 1 in
150 persons infected with WNV develops a more severe form of WNV infection,
including encephalitis (inflammation of the brain). Some individuals with
a severe WNV infection develop rashes, paralysis, inflammation of nerves,
and seizures. Older persons are more susceptible to severe infection with
Special blood tests may be done by local or state health departments
if your doctor suspects you might have WNV infection. Because WNV is a virus,
antibiotics will not work to treat WNV infection. Persons who are ill with
WNV infection usually require hospitalization for supportive care. There is
currently no vaccine for WNV. Research studies are ongoing to find a way to
immunize persons against WNV infection.
Preventing WNV transmission by mosquitoes is the most important way
to decrease WNV infection in humans:
Drain all standing water where mosquitoes breed (birdbaths, old
tires, flower pots, buckets, stagnant puddles or ponds).
Wear protective clothing when mosquito exposure is possible ((long
sleeves, long pants, socks).
Use an insect repellant containing DEET on exposed skin.
Stay indoors during peak mosquito time (dawn, early evening).
Keep windows and screens in good repair.
Also, do not handle dead birds. More than 162 species of birds have
been reported to have WNV infection. Crows have a particularly high death
rate from WNV. Local and state health departments may collect dead birds to
test them for the presence of WNV.
Centers for Disease Control and Prevention888/246-2675http://www.cdc.gov
National Institute of Allergy and Infectious Diseaseshttp://www.niaid.nih.gov/factsheets/westnile.htm
Environmental Protection Agencyhttp://www.epa.gov/pesticides/factsheets/skeeters.htm
National Pesticide Information Center800/858-7378http://www.npic.orst.edu
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Sources: Centers for Disease Control and Prevention, National Institute
of Allergy and Infectious Diseases, Environmental Protection Agency, National
Pesticide Information Center
Torpy JM, Lynm C, Glass RM. West Nile Virus. JAMA. 2003;290(4):558. doi:10.1001/jama.290.4.558