The first human case of the potentially fatal West Nile virus in two years in San Diego County was reported Monday by the county Health and Human Services Agency.
The infection in a 43-year-old Santee man was found during screen of blood he donated. He had experienced no symptoms, which is not unusual for the disease, which is spread by mosquitoes.
The man, who went camping outside the state the week before his blood was drawn, did not recall any recent mosquito bites, according to the HHSA.
"Even though it's most likely this individual acquired West Nile outside of the county, we know the virus is here in San Diego County," Dr. Wilma Wooten, the county's public health officer, said.
"Vector Control collected a dead crow reported by the public in the city of San Diego last week that has also tested positive for West Nile," she said. "It's important for the public to know West Nile virus is a dangerous and potentially deadly disease."
The Vector Control program, part of the county Department of Environmental Health, is inspecting for potential mosquito breeding locations near the man's home and setting up mosquito monitoring traps in the surrounding areas of Santee.
The state Department of Public Health reported 15 West Nile virus-related fatalities in the state last year, but there have been no deaths in the 11 human cases confirmed so far this season.
Most people are infected with the virus from June through October, with the "peak season" in August and September.
Of those who become infected with West Nile virus, 80 percent will have no symptoms, according to the county HHSA. About one in five people who are infected will develop only a mild illness that includes a headache, fever, nausea, fatigue, skin rash or swollen glands.
One in 150 will suffer serious neurologic complications that can become life-threatening. The risk of complications increases for those over age 50, and for people with weakened immune systems.
The county urges residents to prevent mosquito breeding by dumping or removing backyard items that can hold water, such as plant saucers, rain gutters, buckets, garbage cans, toys, old tires and wheelbarrows.
Mosquito fish, available for free from Vector Control, can be used to control breeding of the insect in water sources such as neglected swimming pools, ponds, fountains and water troughs.
Health agency officials said residents can protect against mosquito bites by staying inside when they are most active, between dusk and dawn, and by wearing long sleeves and pants when outdoors. An insect repellent containing DEET, picaridin, oil of eucalyptus or IR3535 can be applied before going outside.
Window and door screens should also be checked to make sure they are in good condition and secured.
The presence of the virus can also be detected in dead birds. Dead crows, ravens, jays, hawks and owls that don't show an obvious cause of death can be reported to Vector Control at (858) 694-2888.
Vector Control will also take reports on green, uncared-for swimming pools, which mosquitoes use for breeding.
