West Nile virus

The ProblemMosquito on arm

Mosquitoes transmit serious and sometimes fatal diseases, such as West Nile virus (WNV), to horses, humans and their pets.

About West Nile virus

WNV is a mosquito-borne virus that is commonly found in Africa, West Asia and the Middle East. In recent years, it has been found in the United States. The onset of symptoms is three to 14 days after being bitten by an infected mosquito. Most people infected with the WNV experience few if any symptoms and recover completely after a few days. Mild symptoms include a fever, headache, body aches, swollen lymph glands and occasionally a skin rash on the trunk of the body. Although rare, some people experience severe infection (West Nile encephalitis or meningitis), with symptoms including headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness and paralysis.

Persons ages 55 or older with preexisting health conditions are more likely to develop severe illness. Symptoms of severe disease may last several weeks, although neurological effects may be permanent.


Mosquitoes become infected with the WNV when they feed on infected birds and can then transmit the virus to humans and animals while biting to take blood. The WNV is NOT transmitted from person-to-person. Other possible transmission routes of the virus are being studied. In areas where the virus is circulating, very few mosquitoes are infected. Even if the mosquito is infected, there is a very low chance that people who get bitten and become infected will get severely ill. The chances you will become severely ill from one mosquito bite are extremely small.

Mosquito Treatment Questions

If you have questions about the frequency of mosquito treatment in your area, or what pesticide is being applied, contact your local municipality or Clarke Environmental Mosquito Management, Inc. at clarke.com.

Effective surveillance of birds and mosquitoes (vectors) is essential to reduce the annual impact of West Nile virus in our community. To learn more about mosquito-borne illness, Wheaton Mosquito Abatement District activities, contact information for Clarke Environmental Mosquito Management, Inc., in addition to what you can do to prevent vector-borne illness, please see Clarke’s 2023 Mosquito Season Update.

Last Reviewed: 1/26/2024