Public Health

The mission of the Butte County Public Health Department (BCPHD) is to protect the public through promoting individual, community, and environmental health. 

West Nile Virus

West Nile Virus (WNV) is a mosquito borne virus most commonly active from June through September. Mosquitoes become infected when they feed on infected birds. Infected mosquitoes can then spread the virus to humans and horses. In a very small number of cases, WNV has been spread through blood transfusions, organ transplants, and from mother to baby during pregnancy or delivery,and possibly through breastfeeding.

The main species of mosquitoes that spread WNV are in the genus Culex. Culex mosquitoes are widespread in California and will feed on birds, humans and other animals. Culex mosquitoes tend to bite in the morning and evening and are not known to spread Zika, dengue, or chikungunya viruses. 

Who's at risk of WNV infection?

  • Anyone living in an area where WNV is present
  • People who work outdoors or participate in outdoor activities

Who's at increased risk of WNV infection?

  • People over the age of 60
  • People with certain medical conditions, such as cancer, diabetes, hypertension, kidney disease, and people who have received organ transplants.

Mosquito & Vector Control in Butte County

The Butte County Mosquito and Vector Control District (District) controls mosquitoes, yellowjackets, and other vectors in Butte County and also in Hamilton City of Glenn County. One of the main goals of the District is to suppress mosquito-borne illnesses such as West Nile virus, Malaria, Zika, Dengue, Chikungunya, Yellow fever, and others. Another goal of the District is to reduce the annoyance level of mosquitoes using environmentally compatible control practices and public education.

Some of the services that the District offers are free mosquitofish, mosquito and yellowjacket annoyance service calls, tick identification, and public education. For more information, to report a dead bird, or to place a request for service please visit the BCMVCD website or call at 533-6038 or 342-7350.

Prevent Mosquito Bites

The most effective way to avoid WNV is to prevent mosquito bites:

  • Use insect repellents when you go outdoors. Repellents containing DEET, picaridin, IR3535, and some oil of lemon eucalyptus and para-menthane-diol products provide longer-lasting protection. Learn more about mosquito repellent.
  • Wear long sleeves and pants from dusk through dawn when many mosquitoes are most active.
  • Install or repair screens on windows and doors. If you have it, use your air conditioning.
  • Help reduce the number of mosquitoes around your home. Empty standing water from containers such as flowerpots, gutters, buckets, pool covers, pet water dishes, discarded tires, and birdbaths.

WNV Symptoms

People typically develop symptoms 3 to 14 days after they are bitten by an infected mosquito. The incubation period could be longer in people with certain medical conditions that affect the immune system.

There is no available WNV vaccine to prevent people from becoming ill from WNV.


No Symptoms

Approximately 80 percent of people (about 4 out of 5) who are infected with WNV do not develop any symptoms.

Mild Symptoms

Up to 20 percent of the people (about 1 in 5) who become infected will display symptoms. Acute symptoms generally last for just a few days, although fatigue and weakness can last for weeks or months. Symptoms may include:

  • fever
  • headache
  • body aches
  • nausea or vomiting
  • swollen lymph glands or a skin rash on the chest, stomach and back 

Serious Symptoms

Less than 1% percent of individuals (about 1 in 150 people) infected with WNV will develop severe neurological illnesses, such as encephalitis or meningitis (inflammation of the brain or surrounding tissue). Serious symptoms may last several weeks, and neurological effects may be permanent. WNV infection can be fatal. Severe symptoms can include:

  • high fever
  • headache
  • neck stiffness
  • stupor, disorientation
  • coma
  • tremors or convulsions
  • muscle weakness
  • vision loss
  • numbness
  • paralysis 

How is WNV Treated?

There is no specific treatment for WNV infection. In cases with milder symptoms, people experience fever and aches that subside on their own. Over-the-counter pain relievers can be used to help reduce fever and relieve associated symptoms. In more severe cases, people may need to go to the hospital where they can receive supportive care, such as intravenous fluids, pain management, and nursing care.

There is no vaccine available to prevent people from becoming infected with WNV.

WNV and Animals

Birds, Squirrels, Cats & Dogs

An infected mosquito can bite any animal, but not all animals will become sick. The disease most often affects birds but may occasionally cause disease in other animals. Wild birds serve as the main host of WNV for mosquitoes. When some species of birds become infected, they produce high quantities of the virus, which can then be passed on to other mosquitoes that bite them. The virus is maintained in this bird-mosquito cycle.

What Should I Do if I Find a Dead Bird?

If you find a dead bird, particularly a crow, jay, magpie, raven, sparrow, finch, or raptor, please file an online report at call toll-free 1-877-WNV-BIRD. Dead bird reports are often the first indication that the virus is active in an area, and this allows the California Department of Public Health (CDPH) to monitor the virus throughout the year.



Tree squirrels with WNV can develop neurological symptoms such as uncoordinated movement, paralysis, shaking, or circling and may die.

Dogs and cats can be exposed to WNV in the same way as humans. However, these animals are very resistant to WNV and rarely become ill. Concerned pet owners should consult with a veterinarian.


Horses can become ill from WNV through the bite of an infected mosquito. Clinical signs of WNV illness in horses may include stumbling, circling, hind leg weakness, inability to stand, drooping lips and lip smacking, hypersensitivity to touch or sound, muscle tremors, and death. The American Association of Equine Practitioners (AAEP) recommends incorporation of a WNV vaccine as an annual core vaccine in equine vaccination protocols. Horse-owners should consult with a veterinarian about the WNV vaccine and other vaccines against mosquito-borne viruses, such as western equine encephalitis.

For more information about WNV and horses, visit the California Department of Food and Agriculture website


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Public Health Department

202 Mira Loma Drive
Oroville, CA 95965

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24-Hour Line: 530.552.4000

Danette York, MPH, Director
Dr. David Canton, Health Officer

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