West Nile Virus

West Nile Virus (WNV) is the leading cause of mosquito-borne disease in the continental United States. Cases of WNV occur during mosquito season, which starts in the summer and continues through fall.

Most people (8 out of 10) infected with West Nile virus do not develop any symptoms. If symptoms do develop, they can include:

  • Fever with other symptoms (headache, body aches, joint pains, vomiting, diarrhea, rash)
  • Serious symptoms affecting the central nervous system (high fever, headache, neck stiffness, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis, death)

West Nile virus is most commonly spread to people by the bite of an infected mosquito.

Severe illness can occur in people of any age; however, people over 60 years of age are at greater risk. People with certain medical conditions, such as cancer, diabetes, hypertension, kidney disease, and people who have received organ transplants, are also at greater risk.

Testing of cerebrospinal fluid to detect WNV-specific IgM antibodies.


  • No vaccine or specific medicines are available for West Nile virus infection
  • Rest, fluids, and over-the-counter pain medications
  • In severe cases, patients often need to be hospitalized to receive supportive treatment, such as intravenous fluids, pain medication, and nursing care.

The best way to prevent West Nile is to protect yourself from mosquito bites by using insect repellent and wearing long clothing to cover skin. There is not a vaccine to prevent WNV infection.

  • Avoid mosquito bites:
    • Use an EPA-registered insect repellent when spending time in areas with mosquitos. Read the label and carefully follow instructions.
    • Use screens on windows and doors, and repair holes in screens to keep mosquitos outside.
    • Stay indoors at dawn and dusk, if possible, when mosquitos are the most active.
    • Wear a long sleeve shirt, long pants, and a hat when going into areas with mosquitos.

  • Take steps to remove and reduce the places that mosquitos live and breed around your home:
    • Mosquitos require water for their larvae.
    • Empty anything that holds standing water: tires, buckets, planters, toys, pools, birdbaths, animal troughs, flowerpots, trash containers, or other places where standing water may collect.
    • If emptying is not possible, cover water sources or change water at least twice per week.
    • Make sure roof gutters drain properly and clean clogged gutters in the spring and fall and fix leaky outdoor faucets and sprinklers.


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WNV Activity and Data