Countywide : Viral Encephalitis Called Growing Risk

An unusually high number of wild birds infected with viral encephalitis, transmitted by mosquitoes, has county health officials concerned that humans may be at increased risk for contracting the disease.

Orange County Vector Control, which monitors wild birds for two strains of viral encephalitis, reports an infection rate 10 to 20 times higher than is normal for June. Infection among the birds is an indication of the prevalence of the mosquito-borne virus.

“It’s really strange. When we saw the data, I had to go back and recheck it,” Vector Control biologist Jim Webb said. “You usually don’t see it until late summer or early fall, but when you see it in April and May, there’s an increased chance that humans may become involved in the transmission cycle.”

Although normally fewer than 0.5% of wild sparrows carry the virus in June, health officials say that number is now around 3%.

“To me, that’s a red flag,” Webb said. “It’s a moderate potential health hazard. I tend to view the worst-case scenario,” Webb said.

In 1984, an encephalitis outbreak in Southern California resulted in 26 people contracting the disease, with one death, county health officials said. Five cases were reported in Orange County.

Children, older people and anyone with an immune system already weakened by recent illness are at higher risk for contracting the virus. Encephalitis--inflammation of the brain--causes headaches, flu-like symptoms and in extreme cases, coma and death, Webb said.

Although there have been no human cases recorded yet this year, he said he expects some to occur locally within the next several months.

“From information on the 1984 epidemic, we found that most of the infections occurred in and around the home,” he said. And although drought conditions may limit the number of natural mosquito breeding grounds, a single water container such as a rain-filled wheelbarrow can produce 10,000 adult mosquitoes in a week.

Residents can reduce their risk by emptying containers and draining areas that collect water and attract mosquitoes.

“We’re trying to get people involved and combine their water conservation with getting rid of the water sources,” he said.

For information, call Orange County Vector Control at (714) 971-2421.