West Nile Virus

Warning: We have West Nile Virus in the Black Hills

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 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.