Encephalitis Virus Found in L.A., Long Beach

Los Angeles County health officials reported Monday that the potentially deadly St. Louis encephalitis virus, a seasonal threat that surfaced last month, has spread to Griffith Park in Los Angeles and El Dorado Park in Long Beach, suggesting that it has become endemic in the county’s mosquito population.

Routine blood samples taken last month from “sentinel chickens” kept in coops in the parks tested positive for the virus, which can cause inflammation of the brain and spinal cord. Authorities received confirmation of the test results Sept. 3, less than a month after announcing that the virus had been detected in birds in Monterey Park and at two Orange County sites.

“Once it gets into the mosquito population, it doesn’t go away,” said Dr. Shirley Fannin, director of disease control programs for the county’s public health department. “It’s probably going to be endemic and be here for centuries.”

But Fannin said the virus--which has not been found in humans since 1992--would be most intense only for the next few months, until cooler weather lowers mosquito activity in the Los Angeles Basin.

“The susceptible people will get it, and either have a mild, moderate or severe case, and that’s it,” she said. “It’s another risk we live with.”

The virus cannot be transmitted from person to person but can be carried from birds to people by mosquitoes. Mosquitoes pass it on to their larvae when they breed. There is no cure.

Health officials from the Greater Los Angeles County Vector Control District said that if weekly surveillance showed increases in the population of the culex tarsalis--the common mosquito that carries the virus--they would consider restricting park hours to keep people out early and late in the day, when mosquito activity is greatest. They have already posted warning signs in the parks.

Technicians from the South Gate-based district will also continue monthly sweeps of potential breeding areas, from flower pots to swimming pools.

Fannin cautioned people to wear insect repellent, pants and long-sleeve shirts if they plan to work outdoors, and urged the removal of standing water--a potential breeding ground for mosquitoes--from yards and garbage disposal areas.

Dr. Jack Hazelrigg, manager of the vector control district, said blood samples from one chicken cooped in Griffith Park and one in El Dorado Park tested positive for the virus. Chickens and wild birds are kept in several Southern California abatement districts as an early warning system. Once a “sentinel chicken” tests positive for the virus, he said, it is removed from the program and released to a public owner. The virus cannot be passed to eggs.

Health experts have been on the lookout for the virus since 1984, when it infected 26 Southern Californians, killing six. Children, the elderly and others with fragile immune systems are most vulnerable. In more than 90% of infections, the virus, named for the city where it was first isolated in 1933, causes nausea and flu-like symptoms, Hazelrigg said.