Reduce Your Exposure to Mosquitoes to Prevent West Nile Virus

Mosquito bites can spread harmful viruses such as chikungunya, dengue, West Nile, and Zika. Estimates suggest that mosquitoes are responsible for killing one million people per year worldwide, making them more deadly than any other living creature.

West Nile virus (WNV) is the leading cause of mosquito-borne disease in the continental United States, according to the Centers for Disease Control and Prevention (CDC). It is commonly spread to people by the bite of an infected mosquito. WNV is transmitted by mosquitoes after they feed on birds infected with the virus. The same mosquitoes can then infect mammals, particularly humans and horses. Cases of WNV occur during mosquito season, which starts in the summer and continues through fall. There are no vaccines to prevent or medications to treat WNV in humans.

Most people infected with WNV do not know they have it or even feel sick. The CDC reports that approximately 1 in 5 people who are infected develop a fever and other symptoms such as muscle weakness or confusion. People typically develop symptoms between 3 and 14 days after they are bitten by the infected mosquito. When a person is infected, early recognition and prompt supportive treatment can substantially lower the risk of developing severe disease.

About 1 out of 150 infected people develop a serious, sometimes fatal, illness such as encephalitis or meningitis (inflammation of the brain or surrounding tissues). People over 50 years of age and those with certain medical conditions, such as cancer, diabetes, hypertension, kidney disease, and organ transplants, are at greater risk for serious illness. Pregnant women and nursing mothers should also consult their healthcare provider if they develop WNV symptoms.

People with milder illnesses typically recover on their own, although symptoms may last for several weeks. In more severe cases, however, patients often need to be hospitalized to receive supportive treatment, such as intravenous fluids, pain medication, and nursing care.

Prevent mosquito-borne diseases by following these recommendations:

  • Use EPA-registered insect repellents containing DEET, picaridin, IR3535, or oil of lemon eucalyptus* when going outdoors. (*Do not use products containing oil of lemon eucalyptus on children under 3 years old.)
  • Wear long sleeves and pants during dawn and dusk hours.
  • Install or repair screens on windows and doors. Use air conditioning, if available.
  • Empty standing water from items outside homes, such as flowerpots, buckets, and children’s pools.

To help remember these key points, experts have suggested using the five D’s--DEET, dress, drain, dusk, and dawn—as a way to help recall the prevention measures needed to avoid mosquito bites and mosquito-borne diseases.

More information about mosquito-borne diseases is available on this website at

Scott Harris, M.D., M.P.H.
State Health Officer