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Chicken Tests Positive for West Nile


LAKEPORT, Calif. – This week’s sentinel chicken testing showed that one of the birds from the Upper Lake flock tested positive for WNV.  As noted in previous press releases, four mosquito samples from Lake County have tested positive for West Nile this year.  The positive samples were collected in Lower Lake (1), Middletown (2), and Upper Lake (2), and all four were the same species, Culex tarsalis, also known as the western encephalitis mosquito.

“This is typically the peak of the West Nile virus season, and activity continues through September,” said Jamesina Scott, Ph.D., District Manager and Research Director of the Lake County Vector Control District.  “Mosquitoes are still biting, and it’s important for residents to dump out any water where the mosquitoes can develop.  To control mosquitoes in ponds, water features, livestock water tanks, or pools and spas that are not being maintained, residents can pick up mosquito-eating fish for free from our office.

“If you plan to be outside when mosquitoes are active, use insect repellent applied according the directions on the label and reapply as directed,” urges Erin Gustafson, Lake County Deputy Health Officer. Dr. Gustafson also encourages residents, “When we see chickens becoming positive for West Nile Virus, the conditions are right for transmission to humans. It is important for medical providers to have an increased awareness and test for West Nile Virus when they have a suspicion.”

The District encourages residents to reduce their risk of contracting West Nile virus and other mosquito-borne diseases by:

  • Dumping or draining standing water to prevent mosquitoes.  Mosquitoes need water to complete their life cycle.
  • Defending yourself.  Use repellents containing DEET, Picaridin, IR3535, or Oil of Lemon Eucalyptus.  Follow the label directions.
  • Avoiding the outdoors when mosquitoes are present, typically dawn and dusk

So far this year, West Nile virus activity has been detected in four mosquito samples and one sentinel chicken in Lake County.  Statewide, 35 California counties have detected WNV this year, mainly in mosquitoes and dead birds.  Thirty-one human cases of West Nile virus illness have been reported in California residents this year.  The most recent confirmed case of WNV infection in Lake County was in 2016.  

Most people (80%) with West Nile virus do not develop any symptoms. 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.


  • See your healthcare provider if you develop the symptoms described above.
  • Your healthcare provider can order tests to look for West Nile virus infection.
  • To learn more about testing, visit the CDC’s Healthcare Providers page.


  • No vaccine or specific antiviral treatments for West Nile virus infection are available.
  • Over-the-counter pain relievers can be used to reduce fever and relieve some symptoms
  • In severe cases, patients often need to be hospitalized to receive supportive treatment, such as intravenous fluids, pain medication, and nursing care.
  • If you think you or a family member might have West Nile virus disease, talk with your health care provider.
  • To learn more about treatment, visit the CDC’s Healthcare Providers page.

Mosquitoes that transmit WNV develop in the standing water found in out-of-service swimming pools and spas, animal watering troughs, ornamental ponds, rain barrels, and similar sources.  Swimming pools and spas that aren’t maintained can produce thousands of biting mosquitoes every day.  Residents can help reduce mosquitoes in their neighborhoods by reporting unmaintained (“green”) pools to the District or pick up free mosquito-eating fish for these sources Monday-Friday 7:30 AM- 4:00 PM from the District at 410 Esplanade, Lakeport.  

Residents with questions or who would like help with a mosquito problem, including reporting a neglected pool or spa, should contact the Lake County Vector Control District at (707) 263-4770 or visit their website at  For more information about West Nile virus, visit  Information about mosquito repellents can be found on the US Centers for Disease Control and Prevention website at


Water Faucet
Urgent Health Advisory

Effective immediately, people on private water systems whose tap water comes from their own private intake into the lake, in the Oaks Arm and Lower Arm of Clear Lake should not drink the water.

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