A Seal Beach woman has died of West Nile virus, Orange County's first fatality from the mosquito-borne illness since 2012, according to public health officials.

Test results Tuesday showed that the unidentified woman, who was in her 80s and had underlying medical conditions, had contracted West Nile neuroinvasive disease, the most severe form of the illness, according to the Orange County Health Care Agency. She is the 10th area resident to die of the virus since it was first reported in humans in Orange County in 2004.

The Orange County Vector Control District recently reported that West Nile has infected 40 people in the county this year — 22 in Santa Ana alone. The disease spreads from birds to mosquitoes to people.

Vector Control also reported that 210 dead birds found throughout the county had tested positive for the virus.

"We had indications early in the summer that this was going to be an epidemic year," said Jared Dever, director of communications at Vector Control. "We knew that by the volume and the prevalence [of disease-carrying mosquitoes] in our traps."

The Health Care Agency and Vector Control are asking residents to wear insect repellent, limit outdoor activity at dusk and dawn and empty all standing water around property to prevent mosquitoes from breeding.

Symptoms of West Nile virus can include fevers, headaches, body aches, convulsions and muscle weakness. Experts say people who believe they may be infected should see a physician immediately.

— Anthony Clark Carpio

Twitter: @acocarpio