The West Nile virus (WNV) appeared in North America in New York
City in 1999 and has since spread across the continental United
States. Predominately spread by the bite of an infected mosquito,
the virus can infect humans, birds, horses, and other mammals. In
most cases, WNV causes a mild flu-like illness or may cause no symptoms
at all. However, the disease can cause severe neurological diseases
such as encephalitis or meningitis in any age group. The elderly
are at very high risk. To reduce the risk of being bitten by mosquitoes,
the following is recommended:
- Suggestions applicable to everyone who lives in or visits an
area where WNV has been found include the following:
- Use a repellent containing DEET when outdoors. Be sure to
follow application directions carefully.
- Minimize time spent outdoors between dusk and dawn.
- Wear socks, shoes, and long-sleeved shirts and pants when
outdoors for long periods, especially when mosquitoes are most
active
- Avoid shady, bushy areas where mosquitoes like to rest.
- Reduce standing stagnant water near your residence.
- Make sure all windows and doors have screens in good repair.
- Horse owners may want to consider the annual vaccination available
for their animals. No vaccine for humans has yet been developed.
While 43 different species of mosquitoes have been identified
in South Dakota, only 9 are known carriers of WNV. Virus cases occur
primarily in the late summer or early fall. Even in areas where
the virus is circulating, few mosquitoes are infected with the virus,
and less than 1 percent of those who get bitten and become infected
will get severely ill.
Twenty percent who become infected will develop mild symptoms,
including fever, headache, and body aches, occasionally with a skin
rash on the trunk of the body and swollen lymph glands. Severe infection
symptoms, which approximately 1 in 150 infected persons will develop,
include headache, high fever, neck stiffness, stupor, disorientation,
coma, tremors, convulsions, muscle weakness, and paralysis. The
time from infection to the onset of the disease is usually 3 to
14 days.
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