A 52-year-old man tested positive for West Nile virus, the first reported case of the mosquito-borne illness in Stanislaus County this year.
Officials said Thursday that the Modesto-area resident became sick and sought treatment from a doctor, but was not tested until he went to donate blood. He was not hospitalized.
On Tuesday, health officials reported the first case of infection in San Joaquin County, a 59-year-old man living in the southern area of the county. He was identified when donating blood and had no symptoms, officials said.
Mosquito populations are on the rise and that raises the risk of infection from a bite. Up to 20 percent of people infected will have symptoms such as a fever, body aches, nausea, vomiting or swollen lymph glands. The symptoms may last for a few days to several weeks.
Less than 1 percent suffer a debilitating attack to their nervous systems, accompanied by fever, neck stiffness, disorientation, coma, tremors and paralysis. This form of the illness can be fatal or cause permanent neurological effects.
People are advised to protect themselves by using insect repellant when outdoors, especially at sunset or sunrise, when mosquitoes are most active. The type of mosquitoes that carry the virus can breed in neglected swimming pools or other water features in neighborhoods, officials stressed.
The East Side and Turlock mosquito abatement districts said they have inspected 2,200 neglected swimming pools, finding breeding mosquitoes in about one-third of them.
In Stanislaus County, six dead birds have tested positive for West Nile virus, and five mosquito samples tested positive in the past week.
Jerry Davis, general manager of the Turlock Mosquito Abatement District, said positive mosquitoes were identified in areas south and east of Turlock, on the outskirts of Denair and north of Denair. But people everywhere in the county are at risk.
"We anticipate there will be increased West Nile virus activity through the summer," said Lloyd Douglass, manager of the East Side Mosquito Abatement District, which includes Modesto and areas north of the Tuolumne River.
The abatement districts have treated more than 62,000 acres to control mosquitoes this year through a combination of ground application and aerial spraying over unpopulated areas.
Either this morning or Saturday, the San Joaquin Mosquito & Vector Control District plans to spray an area northeast of Ripon bordered by Franscella Lane, Highway 120, Murphy Road and South Wagner Road.
Last year, there were 445 people infected with West Nile in 26 counties of California, resulting in 15 deaths. The infections also proved fatal for 17 horses. There is no vaccine for people, but owners are advised to ask their veterinarians about West Nile vaccinations for their horses.
Bee staff writer Ken Carlson can be reached at firstname.lastname@example.org or 578-2321.