COUNTYWIDE : Encephalitis Virus Found Among Birds

A potentially deadly strain of encephalitis has been found in the county, though no human cases have yet been reported, health officials announced this week.

St. Louis encephalitis, which is transmitted by mosquitoes, has been found in a large number of small birds and chickens since Sept. 1, when the county started routine testing for the virus.

“We believe it is the combination of hot, humid days with uncommon warm nights that has contributed to the outbreak,” said Dr. Hildy Meyers, a physician with the county Health Care Agency. The conditions are conducive to breeding of mosquitoes which transmit the virus.

No human cases have been reported, county vector officials said. Although St. Louis encephalitis can cause death in humans, most people exhibit only cold- or flu-like symptoms, allowing the virus to go undetected, said James P. Webb, county vector ecologist.

“The symptoms are so mild that doctors never order a blood test that would reveal the virus,” he said.

The Vector Control District carries out an encephalitis surveillance program that includes testing of wild birds, caged chickens and mosquitoes for the disease. Of 51 house sparrows tested in the Huntington Beach area, five were carrying the virus. A couple of chickens and other fowl in Irvine also tested positive for the virus.

Evidence of the virus has also been detected in chicken flocks in Los Angeles, Imperial and Riverside counties. No human cases have been reported in those counties, health officials say.

Wild birds are the natural reservoirs for the disease. When an uninfected female mosquito bites an infected bird, the virus is transferred to the mosquito. The insect can subsequently transmit the virus to humans through its bites.

The last epidemic of St. Louis encephalitis in Southern California occurred in 1984, causing one fatality among 26 human cases. There were a total of five cases reported in Orange County, with no fatalities.

Because the virus is transmitted by mosquitoes, county officials are asking homeowners to inspect their yards for standing water that the insects could use for breeding.

There are 21 varieties of mosquitoes in Orange County and all require water to breed. But it is not flood control channels and marshes, such as the Bolsa Chica Wetlands and Upper Newport Bay, that are the heavy breeding grounds for the insects. Webb said 60% of the county’s mosquito population use suburban back yards for breeding.

“Those dishes under flower pots and buckets filled with water, even rain gutters, are the places I’m most concerned with,” he said.

Webb also recommends that residents not spend time outdoors during the evening, when mosquitoes are most active, and that they keep themselves covered when outside and use insect repellents. The breeding season should be over by the end of October, he said.

Anyone having problems with large mosquito populations should call the Vector Control District, (714) 971-2421.