Fourth Human West Nile Virus Case Reported In San Diego County

SAN DIEGO, CA — San Diego County health officials are urging residents to take precautions against mosquito bites after confirming the county's fourth human case of West Nile virus this year.

The four cases were identified after symptom onset or positive tests between June 5 and July 14, according to the county. One person was hospitalized for several days, another experienced mild symptoms and did not require hospitalization, and two cases were identified through blood donation screening. One of the infections was acquired locally. No deaths have been reported this year.

West Nile virus is primarily spread to people through the bite of an infected mosquito that previously fed on an infected bird. Health officials said increases in infected mosquitoes and birds often lead to more human cases.

In 2025, the county reported no human cases of West Nile virus but recorded 34 infected dead birds and 182 mosquito batches that tested positive for the virus. So far this year, the virus has been detected in 23 dead birds and 10 mosquito batches. Similar increases have been reported elsewhere in California and neighboring states.

Most people infected with West Nile virus have no symptoms or experience a mild illness that may include fever, headache, fatigue, nausea, rash or swollen glands. In rare cases, the virus can cause severe neurological illness or death. In 2024, an elderly county resident with a compromised immune system died from West Nile virus encephalitis.

County officials encouraged residents to follow three steps: prevent mosquito breeding, protect themselves from bites, and report mosquito activity or dead birds.

Residents can help reduce mosquito populations by eliminating standing water around their homes, including in plant saucers, gutters, buckets, toys, tires and wheelbarrows. The county also offers free mosquito-eating fish for ponds, fountains and unused swimming pools.

To avoid mosquito bites, officials recommend wearing long sleeves and pants outdoors, using insect repellents containing DEET, picaridin, oil of lemon eucalyptus or IR3535, and ensuring window and door screens are in good shape.

Residents are asked to report unusually high numbers of mosquitoes, green swimming pools, standing water, and dead birds such as crows, ravens, jays, hawks and owls to the county's Vector Control Program at 858-694-2888 or by email at vector@sdcounty.ca.gov.

More information is available at SDFightTheBite.com.