A man and a woman walked around a campground near Crystal Lake in Angeles National Forest, wearing gas masks and surgical gloves as they wielded syringes, spray cans of automotive starter fluid and toothbrushes. Five small animals shuffled back and forth in cage-like traps under a nearby tree.
The duo's appearance and equipment were puzzling, almost comical, but their task was very serious. They were preparing to test the captured animals for plague, then kill them to avoid the possibility of spreading the disease.
The two are part of a six-person team run by the Los Angeles County Department of Health Services that monitors "vector borne" diseases, those carried from one organism to another by intermediaries like fleas and mosquitoes.
A large portion of the unit's time is devoted to tracking plague. This ancient scourge, the same "Black Death" that ravaged Europe in the Middle Ages, is alive and well and living in ground squirrels in the hills that ring Los Angeles.
Once a week, inspectors disperse into the hills, checking ground squirrel populations and capturing rodents to test their blood and the fleas in their fur for evidence of plague.
The check at Crystal Lake last summer found that two of the 16 squirrels tested were carrying plague bacteria, the second such finding in the San Gabriel Valley area this year, health officials said. Plague bacteria also were found in squirrels in the eastern part of San Gabriel Canyon in January.
The team also found plague bacteria in the Hollywood Hills in March and in three squirrels captured in Vasa Park, a private picnic ground in Agoura, in June.
Thus far, no other plague bacteria have been found in the foothills of the San Gabriel Valley this year, according to Art Tilzer, director of the county vector control department.
The sites where bacteria were found and surrounding areas have since been posted with warning signs and dusted with insecticide to kill the fleas that spread the disease, Tilzer said. And county agricultural officials plan to set out poison to reduce the squirrel population.
Tilzer said that hikers and campers should not panic because the bacterium, Yersinia pestis, often exists harmlessly in the blood of burrowing rodents.
"It is routinely found in animals around the country," Tilzer said.
But occasionally, for reasons that scientists cannot explain, the bacteria become virulent, causing a "die-off" or "epizootic," the animal equivalent of a human epidemic.
Hosts for Plague
Scientists say that ground squirrels act as what is called the reservoir, or host, for the plague bacteria, according to Frank Hall, the senior biologist in charge of the surveillance program. Some rats are plague hosts, too, but plague has not been seen in Los Angeles' urban rat population for decades, Hall said.
Fleas are the vector, the carrier of the bacteria from animal to animal or to man.
"Man becomes accidentally involved in plague when the squirrel dies and the flea leaves looking for a warm blooded-animal," Tilzer said.
"What we have done at Crystal Lake as a result of the findings is kill off the fleas," Tilzer added. "There are no signs of die-off in the area."
Dr. Shirley Fannin, associate deputy director of disease control programs for the county, said, "While ground squirrels stay alive, the fleas will stay on their bodies.
"But if you get a die-off, then an area can be hopping with infected fleas. When some warm body walks by, they jump on and take a blood meal wherever they can," she said.
The warm body can be that of a person or a pet, she said. House pets infested with plague-carrying fleas can become a bridge, carrying the fleas into contact with humans.
Cases of plague in humans are rare, according to Allan Barnes, director of the plague branch of the federal Centers for Disease Control in Fort Collins, Colo. Only six cases have been reported this year in the United States; one of those was in Nothern California.
The two most recent cases of bubonic plague in Los Angeles County occurred in 1984, and both involved residents of the San Gabriel Valley.
That year a Claremont veterinarian contracted the disease from an infected cat. Tilzer said that the cat had an open sore and the bacteria could have passed from the cat's blood to the man if the man had a cut and touched the sore. Another possibility, he said, was that the man got it when the cat sneezed or coughed.
Since the cat was in an advanced state of infection, the bacteria had reached its lungs and it had acquired pneumonic plague.
The other person was a woman from Bradbury who had visited a campground near Bakersfield and contracted the disease there. When the disease surveillance staff went to the campground, they found plague-infected animals.
Both victims were cured.