Solano County Mosquito Abatement District

CALIFORNIA SURVEILLANCE AND FACTS ABOUT WEST NILE VIRUS

- What is West Nile virus?
- How do people and animals get West Nile virus?
- What are the symptoms of West Nile virus in people?
- Which animals get West Nile virus?
- West Nile Virus Protection & Control
- What is the California West Nile Surveillance Program?
- What do I do if I see a dead bird?

What is West Nile virus?
West Nile virus (WNV) is a mosquito-borne virus that has been found in parts of Asia, eastern Europe, Africa, and the Middle East. The virus was first detected in the United States (U.S.) in 1999 in New York City.

The majority of people and animals that are infected with the virus have a mild illness or no symptoms. In rare cases, the virus can cause a more serious condition called encephalitis, an inflammation of the brain. The elderly are at a higher risk for disease caused by WNV. In 2002, a total of over 44 states reported WN virus activity and over 4000 human cases were reported including over 250 deaths.

In California, one human case of locally-acquired WNV was found in Los Angeles County. Further WNV activity was not found in the state in 2002.

How do people and animals get West Nile Virus?
WNV is transmitted to people and animals by infected mosquitoes. Only certain species of mosquitoes carry the virus and very few mosquitoes are actually affected. A mosquito first acquires the infection by feeding on a bird with virus in its blood. The virus lives in the mosquito and is transmitted to a new host in the mosquito's saliva when the insect bites into a person or animal. The virus is most prevalent from May to October when mosquitoes are most abundent.

Human-to-human transmission of WNV generally does not occur. However, human WNV infection was associated with blood transfusions and organ transplants from infected donors in 2002.