Los Angeles County West Vector & Vector-Borne Disease Control District


West Nile Virus




Current West Nile Virus Activity in Los Angeles County

Click on the pictures below for

 2018 and 2019 activity




What is West Nile Virus?

West Nile is a virus most commonly spread to people by mosquito bites. In North America, cases of West Nile virus (WNV) occur during mosquito season, which starts in the spring/summer and continues through fall. WNV cases have been reported in all of the continental United States, including Los Angeles County.

How do people get infected with WNV?

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Mosquito Bites:
West Nile virus is most commonly spread to people by the bite of an infected mosquito. Mosquitoes become infected when they feed on infected birds. Infected mosquitoes then spread West Nile virus to people and other animals by biting them.

In a very small number of cases, West Nile virus has been spread through:
   Exposure in a laboratory setting
   Blood transfusion and organ donation
   Mother to baby, during pregnancy, delivery, or breast feeding

West Nile virus is not spread:
   Through coughing, sneezing, or touching
   By touching live animals
   From handling live or dead infected birds. Avoid bare-handed contact when handling any dead animal. If you are disposing of a dead bird, use gloves or double plastic bags to place the carcass in a garbage can.
   Through eating infected birds or animals. Always follow instructions for fully cooking meat from either birds or mammals.

Who is at risk for infection with WNV?

Anyone bitten by a mosquito in an area where the virus is circulating can get infected with WNV. The risk is highest for persons who engage in outdoor work and recreational activities. Elderly persons are at increased risk of severe disease if they are infected.

How soon do people get sick after getting bitten by an infected mosquito?

It takes 2-14 days after the bite of an infected mosquito to develop symptoms of WNV.

What are the symptoms of WNV?

No symptoms in most people. Most people (8 out of 10) infected with West Nile virus do not develop any symptoms.

Febrile illness (fever) in some people. About 1 in 5 people who are infected develop a fever with other symptoms such as headache, body aches, joint pains, vomiting, diarrhea, or rash. Most people with this type of West Nile virus disease recover completely, but fatigue and weakness can last for weeks or months.

Serious symptoms in a few people. About 1 in 150 people who are infected develop a severe illness affecting the central nervous system such as encephalitis (inflammation of the brain) or meningitis (inflammation of the membranes that surround the brain and spinal cord).
 Symptoms of severe illness include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis.
 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.
 Recovery from severe illness might take several weeks or months. Some effects to the central nervous system might be permanent.
 About 1 out of 10 people who develop severe illness affecting the central nervous system die.

What should I do if I think a family member or pet might have a mosquito-borne disease?

Consult a healthcare provider for proper diagnosis.