Stanislaus County health officials reported Tuesday that four people have been infected with serious cases of West Nile disease.

The county Health Services Agency said in a news release the local cases are the first in 2023. The four adults were stricken by the dangerous neurological form of the illness.

Their names and city of residence were not released. The patients were hospitalized. No information was available on their current medical conditions.

West Nile disease usually is spread to people through the bite of infected mosquitoes. The county’s mosquito abatement districts first detected the endemic virus in mosquito samples in June.

The county also has reported one case of an infected horse.

“Because there is no vaccine and no specific treatment for West Nile virus, it is important for people to take steps to protect themselves and their families from mosquito bites,” county Public Health Officer Thea Papasozomenos said in the news release. “We also urge residents to help control the mosquito population by dumping and draining any standing water around their homes, and reporting neglected swimming pools, as these can serve as mosquito breeding sites.”

Most people bitten by an infected mosquito won’t have noticeable symptoms. About 20% develop mild symptoms, and fewer than 1% develop a serious illness, such as encephalitis or meningitis, which usually puts victims in the hospital. The serious illness may result in long-term disability and can be fatal.

Older adults and people with chronic health problems are more susceptible to the neurological illness.

More than 30 cases of West Nile disease have been tabulated statewide this year, including two fatalities. More than 300 people have died from West Nile in California since 2003.

The county recommends precautions to keep from getting infected, including using insect repellent and wearing long sleeves and long pants when going outdoors in the evening or early morning, when mosquitoes are feeding. Also, drain standing water around the home from flower pots, bird baths, gutters and containers.

Residents may report dead birds (which are natural hosts), especially crows, jays and ravens, to the California West Nile Virus Center at 877-968-2473.

Mosquito problems can be reported to Turlock Mosquito Abatement District at 209-634-1234; Modesto-area residents should call East Side Mosquito Abatement at 209-522-4098.