Prospective Blood Donor Is Year’s First Case of West Nile Virus in O.C.

A 44-year-old South County man became the first person this year to test positive in Orange County for West Nile virus, health care officials said Thursday.

The discovery was made this month when the unidentified man failed a routine screening while donating blood, said Deanne Thompson, spokeswoman for the county Health Care Agency.

The man showed no symptoms and may have acquired the virus as long as 30 days ago while traveling outside the county, Thompson said.

This year, 58 people have fallen ill with the virus in California, including an elderly woman who died this week in Butte County. Last year at this time, there were 174 cases.

Riverside County health officials on Thursday confirmed their first human case this year. A 53-year-old Moreno Valley resident was hospitalized with the disease but has since returned home, according to local health officials.

The West Nile virus, first detected in California in 2002, usually is passed to humans through mosquitoes that have bitten infected birds.

About 80% of humans infected with the virus don’t realize it, officials say. Nearly 20% experience mild to moderate flu-like symptoms.

In fewer than 1% of cases, a potentially fatal complication, such as encephalitis or meningitis, can develop.

The first signs of West Nile in Orange County this year occurred in July when authorities found 19 infected mosquitoes in traps they had set up in Craig Regional Park in Fullerton. Officials added more traps and sprayed the area.

Health officials cautioned residents to check their window and door screens to make sure there are no gaps, and to empty standing water on their property. Officials recommend that those who go outdoors should wear long pants and long-sleeved shirts and apply insect repellent.

Times staff writers Susannah Rosenblatt and Rong-Gong Lin II contributed to this report.