West Nile virus, a disease that is typically transmitted to people by mosquitos that have fed on blood from infected birds, has infected six people in California so far in 2026, including the San Joaquin Valley’s first three human cases of the year in Tulare, Kings and Fresno counties..

By this time last year, the California Department of Public Health had confirmed only three human cases of the virus statewide. The five-year average for this point in the mosquito season is 2.4 cases among humans in the state.

In an announcement issued July 24, the Kings County Department of Public Health said its lone confirmed case of 2026 comes about two weeks later than last year’s first case.

Fresno County’s Department of Public Health also issued a statement on July 24 about its first confirmed case of 2026, detected through routine testing of a blood donor. “The number of human WNV cases is expected to increase, as it is still peak mosquito season in Fresno County,” the agency said.

“We need to stay vigilant as mosquitoes may continue to cause many severe illnesses, including West Nile virus infection, which can require hospitalization and intensive care,” Fresno County Health Officer Dr. Trinidad Solis said in the prepared statement.

None of the three Valley counties released details on where the cases had occurred or information on those who have been infected.

The other California counties to report human cases of West Nile were Sacramento, Los Angeles and San Diego counties, each with one incidence of the disease.

The U.S. Centers for Disease Control reports that so far in 2026, 91 instances of human West Nile infections have been confirmed in 20 states as of July 21. 

As part of a West Nile surveillance program, counties and the state trap mosquitoes, chickens and dead birds to monitor the spread of the virus. As of July 24, the virus has been identified in 670 mosquito samples, 251 dead birds, two chickens and one horse in addition to the six human cases statewide.

In 2025, the California Department of Public Health confirmed 117 human cases of West Nile virus in the state – the third-lowest total in more than 20 years – of which 11 proved fatal.

Health officials report that most people who become infected by West Nile experience no symptoms at all. About 20% have mild symptoms that can include fever, headache, body aches, nausea and vomiting.

But for some people, including the elderly or those with compromised immune systems, the virus can cause severe neurological illness and death.

West Nile virus is the leading cause of mosquito-borne illness in the U.S. The CDC estimates that about 2,000 people are diagnosed each year, but most cases are believed to go unreported because the victims either experience no symptoms or think their symptoms are related to some other cause.

More than 1,300 people each year develop a serious case of West Nile affecting the central nervous system, with about 130 deaths per year. There are no licensed vaccines or medicines to prevent or treat West Nile disease in humans, the CDC reports.

Health officials warn that to protect against West Nile or other illnesses carried by mosquitos, residents can:

  • Use an insect repellent containing DEET, picaridin, oil of lemon, eucalyptus or Insect Repellant 3535 to keep mosquitoes from biting.
  • Wear long sleeves and long pants, as well as using mosquito repellent, during the early morning and evening hours when mosquitoes are most active.
  • Make sure that screen doors and window screens are tight-fitting to keep mosquitoes outside, and to repair damaged or torn screens.
  • Eliminate or drain sources of standing water where mosquitoes can lay their eggs. This includes flower pots, buckets, old car tires and other containers. Swimming pools that are not properly maintained and have green or stagnant water can also be a breeding ground for mosquitoes.

Tim Sheehan is the Health Care Reporting Fellow at the nonprofit Central Valley Journalism Collaborative. The fellowship is supported by a grant from the Fresno State Institute for Media and Public Trust. Contact Sheehan at tim@cvlocaljournalism.org.