The county's West Mosquito Abatement District is monitoring the La Brea Tar Pits as part of a campaign to reduce the threat of the rare and potentially fatal St. Louis encephalitis virus.
The district this month placed 20 hens in a wood-and-wire chicken coop in a park outside the tar pits, a prime breeding location for mosquitoes. Because the disease is carried by birds and transmitted by mosquitoes to other animals, the "sentinel flock" of chickens will act as an "early warning system," Norman Hauret, district manager, said.
Hauret said monthly blood samples taken from the chickens will be sent to the state health department's virus laboratory in Berkeley for analysis, as will mosquitoes trapped in the area.
Two varieties of mosquitoes--the Culex tarsalis and the Culex quinquefasciatus-- are known to transmit the virus. The insect's breeding cycle peaks in the summer.
State and county health officials warned of the possibility of an epidemic last year when 26 cases of St. Louis encephalitis were reported in heavily populated areas of Southern California. Sixteen cases, including one fatality, occurred in Los Angeles County.
What baffles most officials is that St. Louis encephalitis is usually found in natural mosquito breeding grounds in rural or swampy areas. Dom Womeldorf of the state health department called last year's outbreak "unprecedented. It . . . caught everybody by surprise, because there is no history of it."
The state's last major outbreak of encephalitis occurred in 1952 in the Central Valley, where 500 people were affected.
No new cases have been reported this year.
But Ronald Perkins, president of the board of trustees of the mosquito abatement district, said, "The potential is there, like anything else. If you compare the 26 cases with all the millions of people in the Southern California area, the percentage might seem low. But when you look at the fact that we haven't had the virus for a long time, then it starts to become more alarming."
Added Hauret, "We are gearing up so that there is not a repeat of last year."
Public's Help Sought
Officials have asked for the public's help in controlling the mosquito population. Hauret said residents should try to eliminate standing pools of water in their backyards and neighborhoods--such as swimming pools, bird baths, old tires and discarded containers--where mosquitoes are likely to breed.
Hospitals have also been asked to be on the lookout for patients suffering from encephalitis, which has flu-like symptoms. The disease often goes unreported because most people experience only the early symptoms, said Betty Agee, who heads the county Department of Health Services' section on acute communicable disease control. "For every one case that is diagnosed, there are about 200 where it is not identified," she said.
In more serious cases, the virus has been known to result in brain damage and death. The greatest threat is posed to infants and the elderly.
State legislation that would have provided the abatement district with $3.5 million to help combat the potential outbreak was voted down this week in the Assembly's Health Committee. The bill would have increased mosquito eradication programs and encouraged the formation of additional mosquito abatement districts.