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West Nile Virus

West Nile Virus (WNV) causes an infection in horses, birds and humans. People and animals get the virus when they are bitten by an infected mosquito. There is no evidence that West Nile virus can spread from one person to another or from an animal to a person.


In humans, the virus usually does not produce symptoms in people who are infected.  Those who do get ill from the virus usually experience symptoms within five to 10 days after being bitten by an infected mosquito. Their symptoms can include fever, headaches, body aches, swollen glands and a rash.  People above age 50 face the greatest risk of severe illness due to West Nile Virus.

Less than one percent of infected people develop encephalitis from West Nile Virus. This severe illness can cause convulsions, paralysis and even death.

Protecting yourself

The best way to protect yourself against West Nile Virus is to minimize your exposure to mosquitoes.  There are several things you can do to protect yourself:

  • Wear long pants and long-sleeved shirts.
  • Wear earth-tone colors, such as olive, khaki and brown.  Mosquitoes are attracted to contrast, and these colors will reduce that contrast.
  • Use a mosquito repellent containing DEET. Apply it sparingly to exposed skin and clothing. Follow all directions on product labels. The American Academy of Pediatrics recommends repellents used on children contain no more than 10 percent DEET.
  • Make sure windows, doors and screens are bug tight.
  • Use the proper type of lights outside: incandescent lights attract mosquitoes; fluorescent lights neither attract nor repel mosquitoes.
  • Stay indoors at dawn, dusk, and early evening when mosquitoes are most active.
  • Spray trees and shrubs just before you plan to spend time in your yard. Insecticides for use in and around your home are available as ready-to-use sprays, aerosols, and concentrates to be diluted in water or used in foggers. Look for products containing carbaryl, cyfluthrin, malathion, permethrin and pyrethrins. Read labels closely to be sure you are getting the product you need and are applying it in the way it was intended.  

The best way to reduce our mosquito population is to eliminate the places where mosquitoes breed.  Standing water provides the ideal breeding ground for mosquitoes.  Please follow these steps to help control the mosquito population:

  • Put away water-holding containers such as tires, buckets, trash cans, flowerpots, toys, etc.
    Properly care for backyard pools and frequently change water in birdbaths and wading pools.
  • Treat water in water gardens or fountains if the water does not flow on a regular basis. You can purchase a larvicide at local home improvement stores and use it to kill mosquitoes in the water before they hatch. Products known as BTI, mosquito dunks and Altosid are examples of larvicides.
  • Drain or fill in low areas in your yard; clean drains, ditches, and culverts to ensure proper drainage.
  • Repair leaks on faucets or air conditioning units.
  • Ensure adequate drainage of sump pump discharge.
  • Keep grass and shrubs around your home trimmed well.

How we monitor for West Nile Virus

Fargo Cass Public Health (FCPH) will collect dead birds this year as part of its surveillance program for West Nile Virus. A large number of dead birds can indicate the presence of West Nile because birds are highly susceptible to dying from it. Learn more.

Cass County Vector Control performs frequent tests on mosquitoes to determine if West Nile Virus is present.

Background information

Scientists first identified West Nile Virus in Africa in 1937. It has also been found in the Middle East and Europe along major bird migration flyways that connect Europe, Africa, and the Middle East. The virus first appeared in North America in the summer of 1999 in New York City.  At that time, it caused 62 cases of neurological disease and seven deaths in humans.

For more information

The Centers for Disease Control offers more detailed information on West Nile Virus.

The Environmental Protection agency offers information on using repellents safely, what you should know about the repellent ingredient DEET, and the use of pesticides for mosquito control.