SACRAMENTO — The California Department of Public Health (CDPH) reports that West Nile virus (WNV) activity in California has reached its highest level in five years, prompting health officials to urge residents to protect themselves from mosquito bites during the peak transmission season.

As of August 14, 2026, California had reported 30 human cases of WNV, including three deaths, across 13 counties. The number of cases is higher than the five-year average for this point in the year.

Evidence of WNV activity has been detected in 32 California counties through surveillance of mosquitoes, dead birds, sentinel chickens and horses. More than 24% of tested dead birds have been positive for the virus, compared with a five-year average of 13%. About eight out of every 1,000 tested mosquitoes are currently positive, compared with the five-year average of five per 1,000.

“West Nile virus can be fatal, particularly for older adults and people with weakened immune systems,” said CDPH Director and State Health Officer Dr. Erica Pan. “August and September are peak periods for West Nile virus transmission in California, so we urge everyone to take precautions against mosquito bites.”

WNV is transmitted to humans and animals through the bite of an infected mosquito. Most people face a low risk of serious illness, but some may develop severe neurological conditions, including encephalitis or meningitis, which can be fatal.

People at greater risk of severe illness include those age 60 and older, individuals with diabetes, hypertension or chronic kidney disease, and those taking medications that suppress the immune system.

Follow the “Three Ds” of Mosquito Prevention

DEET: Use an EPA-registered insect repellent containing DEET, picaridin, oil of lemon eucalyptus or IR3535, following label directions.
Dawn and Dusk: Mosquitoes that spread WNV are most active during the early morning and evening. Wear loose-fitting, long-sleeved shirts and pants, apply repellent, and make sure doors and windows have properly fitted screens.
Drain: Remove standing water from flowerpots, tires, buckets and other containers where mosquitoes can lay eggs. Report neglected swimming pools to your local mosquito and vector control agency.

Californians can help health officials track the spread of WNV by reporting dead birds at WestNile.ca.gov** or by calling 1-877-WNV-BIRD (968-2473).

People taking immune-suppressing medications should speak with their healthcare provider about their risk of serious illness and take extra precautions to prevent mosquito bites.