West Nile Virus Information

Education and resources for prevention and treatment

West Nile Virus (WNV) is a disease people can get from being bitten by an infected mosquito. The disease is usually not serious, but some people can become very ill. There is no vaccine for humans that will prevent WNV. The best way to prevent WNV is to prevent mosquito bites.

For most people the risk of catching WNV is low. Being outside a lot puts you at higher risk, especially if you are outside when mosquitoes are most active, at dawn and dusk. People over 50 years of age have a higher chance of getting sick when infected with WNV, and should be careful to avoid mosquito bites. If you go outside when mosquitoes are active, put on insect repellent containing DEET, picaridin, oil of lemon eucalyptus, para-menthane-diol or IR 3535. Follow the directions on the label. You can help prevent mosquitoes from breeding by draining all standing water on your property.

Fight Back - Protect yourself and your family

Practice the Seven Ds:

  • DRAIN any standing water that may produce mosquitoes, including unmaintained
    swimming pools.
  • DAWN and DUSK are times to avoid being outdoors. These are the times when mosquitoes are most active.
  • DRESS appropriately by wearing long sleeves and pants when outside.
  • DEFEND yourself against mosquitoes by using an effective insect repellent such as
    DEET, Picaridin or Oil of Lemon Eucalyptus. Follow label directions.
  • DOOR and window screens should be in good working condition to prevent mosquitoes from entering your home.
  • DISTRICT personnel are available to address any mosquito problems you may be experiencing by calling 342-7350.

What can you do if you see a mosquito problem or stagnant water problem?

To report mosquito problems or standing water call: Butte County Mosquito & Vector Control District at (530) 342-7350 from Chico or (530) 533-6038 from Oroville; Durham Mosquito Abatement at (530) 345-2875; or Oroville Mosquito Abatement at (530) 534-8383.

Learn more at Ask about availability of free mosquito-eating fish for ornamental pools, ponds or stagnant swimming pools that cannot be immediately cleaned.

What can you do if you find a dead bird?

Dead birds may be a sign that West Nile virus is circulating between birds and the mosquitoes in an area. To help monitor the presence of West Nile Virus in your community, report dead birds by calling the California Department of Public Health's West Nile Virus program at 1-877-WNV-BIRD (1-877-968-2473). Operators are available from 8 a.m. to 4:30 p.m., Sunday through Friday. After 5 p.m., please leave a message. In addition, you can report a dead bird anytime by visiting the California West Nile Virus website.

Due to the high volume of reports, the California Department of Public Health is unable to respond to each report. However, all of the information received about dead birds is used by public agencies to track where birds are dying. This allows the local mosquito and vector control agencies to concentrate mosquito control efforts in those areas.

How is WNV transmitted?

West Nile Virus is transmitted to humans and animals through a mosquito bite. mosquitoes become infected when they bite and feed on infected birds. WNV is not transmitted by person-to-person contact. The California Department of Health Systems said there's evidence that WNV can be acquired via a blood transfusion or organ transplant from an infected donor, and from breastfeeding or during pregnancy from mother to baby, although it said this is unlikely.

What can happen if you become infected with WNV?

No symptoms for most people. Most individuals (about 80 percent) who are infected with WNV will not experience any illness.

Mild symptoms for some people. Others (about 20 percent), will have only mild symptoms, such as fever, headache, body aches, nausea and vomiting and sometimes swollen lymph glands or a skin rash on the chest, stomach or back, according to the California Department of Health Systems (CDHS). Symptoms can last a few days, though even health people have been sick for several weeks.

Serious symptoms for few people. WNV can be severe in the elderly and individuals with weakened immune systems. About 1 in 150 people develop serious symptoms, according to the CDHS. Severe symptoms can include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis; these symptoms may last several weeks, and neurological effects may be permanent.

How soon do infected people get sick?

If people develop symptoms, it typically happens between 3 and 14 days after they are bitten by the infected mosquito, according to CDHS.

How is WNV infection treated?

There is no specific treatment for WNV infection. In cases with milder symptoms, the symptoms pass on their own. In more severe cases, people usually need to go to the hospital where they can receive supportive treatment including intravenous fluids, help with breathing and nursing care, according to the CDHS.

Is there a vaccination against WNV?

There is no vaccine to prevent WNV in humans. However, there is a vaccine for horses.


For recorded information on West Nile Virus, call the Enloe West Nile Virus Hotline at (530) 332-7017. For more information, try the following contacts:

Local Mosquito & Vector Control District Offices:

  • Butte County Mosquito & Vector Control: (530) 342-7350 from Chico or (530) 533-6038 from Oroville or
  • Durham Mosquito Abatement District: (530) 345.2875
  • Oroville Mosquito Abatement District: (530) 534.8383

Horse owners: Call your local veterinarian, or try this sites for further reading and resources: