County sees first case of rare mosquito-borne disease in 47 years

STOCKTON — A Stockton resident has been diagnosed with St. Louis encephalitis virus this week, the first time a human case had been reported in San Joaquin County since 1973.

San Joaquin County Public Health Services said the person infected with the virus is recovering at home. An age and gender were not disclosed.

The symptoms and transmission of SLEV is similar to West Nile virus, according to county public health, but it is less common in California.

People can contract SLEV from the bite of an infected Culex mosquito, which in turn can become infected after biting a bird that carries the virus, county public health said. The virus is not spread from human to human.

Most people infected with SLEV do not have any symptoms or develop mild symptoms, which include fever, headache or nausea, all of which can occur as much as to two weeks after being bitten.

In rare cases, SLEV can cause swelling or inflammation of the brain, which may lead to death. Older adults are most at risk to become very sick if they are infected, according to county public health.

The Stockton resident is the second in the state to report contracting SLEV this year. According to the California Department of Public Health, Madera County has also reported a human case of SLEV, as well as 17 mosquito samples carrying the virus.

The report of human infection comes two months after San Joaquin County Public Health reported a sample of mosquitoes carrying SLEV was found in Lodi’s 95240 ZIP code.

The sampling was also the first found in the county since 1973. There have been a total of two samples collected from mosquitoes in the county.

Stanislaus County has also reported collecting two samples of the virus, and a total of 504 samples have been found statewide.

While the symptoms of SLEV are similar to West Nile virus, there has been only one reported human case of West Nile virus in San Joaquin County this year, from an asymptomatic blood donor, county public health said.

However, there have been 258 samples of mosquitoes found carrying West Nile virus, the fifthhighest amount in the state.

Four dead birds infected with WNV have been found in the county, along with three infected horses.

Stanislaus County has reported 32 cases of WNV and 350 collected mosquito samples, the second-highest in the state behind Los Angeles County.

Sacramento County has reported one case and 115 collected mosquito samples, while Calaveras and Amador counties have no reported cases or samples.

To help reduce the risk of getting St. Louis encephalitis or West Nile virus, county public health and the San Joaquin Mosquito and Vector Control District encourage residents to:

• Eliminate all standing water on your property where mosquitoes can breed.

• Apply insect repellent when outdoors that contains EPA registered active ingredients including DEET, Picaridin, oil of lemon eucalyptus, or IR3535. Follow the label’s instructions.

• Avoid spending time outside at dawn and dusk, and especially for the first two hours after sunset, when mosquitoes are most active.

• If outdoors when mosquitoes are active, wear long pants, loose-fitting/long-sleeved shirts, and other protective clothing.

• Exclude mosquitoes from your home with tight-fitting screens on doors and windows.

For more information about St. Louis encephalitis virus, visit

Report daytime biting mosquitoes or significant mosquito infestations to the mosquito district at www.sjmosquito.

org, 209-982-4675 or 800300-4675.