Davis resident hospitalized in Yolo’s first human West Nile infection of 2025

A Davis resident has been hospitalized with Yolo County’s first confirmed human case of West Nile virus this year, county health officials announced Thursday.

The case is among 16 reported statewide so far this year and follows a severe infection earlier this month in Butte County. Health officials said the virus is most active during the summer, with August typically marking the peak of West Nile transmission in Northern California.

“This case serves as a reminder that West Nile virus remains a threat in Yolo County,” said Dr. Aimee Sisson, the county’s public health officer. “Just one bite from an infected mosquito can transmit West Nile virus. Most people who become infected don’t get sick, but about one percent of individuals develop a serious neurologic illness.”

The county urged residents to “take precautions to protect themselves from mosquito bites.”

To reduce risk, county health officials recommend draining standing water, avoiding outdoor activity at dawn and dusk, wearing long sleeves and pants, and using insect repellent with DEET, picaridin or lemon eucalyptus oil.

West Nile virus symptoms can develop two to six days after a bite. Most individuals have no symptoms though one in five infections can cause fever, nausea, headaches or body aches. Older adults and those with chronic conditions face a higher risk of complications requiring hospitalization, the county said.

Yolo is the eighth county in the state to see human cases of the virus. Other human cases have been located in the San Joaquin Valley from Tuolumne and Stanislaus counties south to Kern County.

The Butte County Department of Public Health reported the Sacramento Valley’s first 2025 case on Aug. 15. The infection occurred in a person in their 30s or 40s who was also battling a separate severe infection. Of the 16 statewide cases so far, one has resulted in death, according to the California Department of Public Health.