Encephalitis Virus May Remain for Long Time, Authorities Fear

A potentially fatal mosquito-borne encephalitis virus that began to flourish in Southern California last fall, killing at least one person, may have found a new long-term home in Los Angeles and Orange counties, state and county health officials say.

The outbreak of St. Louis encephalitis late in 1984 was the first of its magnitude on record in a heavily populated urban area in California, said Charles Myers, regional supervisor for vector biology in the state Department of Health Services.

“The general opinion was that it couldn’t happen here,” he said. “It’s supposed to happen only in sparsely settled agricultural areas, and there was no record of it elsewhere until 1983, when we had two cases in Los Angeles. Then suddenly in 1984, we had 16 in Los Angeles, five in Orange County, four in Riverside County and one in San Diego County.”

One of the 1984 victims, a woman in her early 60s, died in January, Los Angeles County health officials said.

‘New Phenomenon’

“It’s a new phenomenon in this area, and it looks like it might now be endemic” to Los Angeles and Orange counties’ metropolitan sectors, said Laurie Habel, epidemiologist with the Los Angeles County Department of Health Services.

One of the first reports of the presence of the virus-carrying mosquitoes in an urban Southern California neighborhood came early last September when it was learned they were breeding in a marsh in Irvine.

The discovery was made when several chickens in a so-called “sentinel flock,” maintained by the Orange County Vector Control District to monitor insect populations, were found to have traces of the virus in their blood. At about the same time, similar evidence turned up in a flock near San Pedro.