Plague Hunters in Combat Against Ancient Enemy

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.

Weekly Tests

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.

Infected Cat

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.

Plague has been monitored by the federal government since the turn of the century, when it was placed on a list of potentially catastrophic diseases by an international body that later became the World Health Organization, Barnes said.

Two Types of Plague

When the bacteria infect humans, the disease can take bubonic or pneumonic form. Bubonic plague is characterized by swollen lymph nodes and a high fever. It develops slowly over a few days and is not very contagious. If not treated, it can be fatal. Pneumonic plague attacks the lungs.

Both forms of plague can be treated with common antibiotics, but pneumonic plague progresses so swiftly that treatment often comes too late.

“The mean time from start to death is 1.8 days” for pneumonic plague, Barnes said. It can be spread through a cough or sneeze.

The full destructive potential of plague last was felt in the United States in 1924, Barnes said, when an epidemic swept a small section of downtown Los Angeles and killed 33 people in a three-week period.

Ripe Situation

“The situation was really ripe,” said Fannin, adding that there were huge populations of rats in Chinatown and ground squirrels in the Chavez Ravine area, where Dodger Stadium now stands.

“The disease went rapid-fire from one human to another,” she said, and was stopped when 10 square blocks were cordoned off by armed guards. Within a decade, Los Angeles had put together a major rat-control program, she said, and plague was not seen in the city again until the 1970s.

Health officials said that plague came back not in the urban areas but mostly in communities next to the mountains, like Diamond Bar and Bradbury.

Tilzer said that the bacteria are found in the county from three to 10 times a year. Over the last 10 years, plague bacteria have been found in Azusa Canyon, Claremont, Bradbury and more than a dozen locations in Angeles National Forest.

Fannin said the vector unit was started in 1979 in an effort to understand how the disease is distributed in ground squirrels and how to control it. Members of the surveillance unit, who go out every day of the week, periodically visit about 400 sites around the county to conduct surveys of squirrel populations.

The highest priority is given to popular camping and park areas where there are many squirrels, Hall said.

The squirrel population is calculated by counting burrows, counting squirrels that are above ground and estimating the number that might be out of sight, he said.

On subsequent visits, a significant drop in the squirrel population can thus be quickly noticed.

What the scientists hope not to find is evidence that a “die-off” is in progress, Hall said. One indicator is abandoned burrows, which are sometimes covered with cobwebs. Flies buzzing around a burrow entrance also signal a die-off, he said.

Setting Traps

At some sites, traps--wire-mesh containers the size of shoe boxes in which animals are caught alive--are set, so that samples of blood and fleas can be taken from them.

As the inspectors start the testing procedure, the reason for each item in the inspectors’ odd armamentarium becomes clear. The spray cans of starter fluid, normally used to drive water from a damp carburetor, contain ether and thus make an economical anesthetic. All the animals remain unconscious throughout the procedure and are killed with an extra dose of ether.

“It seems cruel,” Hall said, but he added that if a blood sample from a tested animal later turned out to be positive for plague and that animal had been released, the department might be held responsible for any consequences.

The ether, along with the possibility of disease in the animals, make the gas masks a necessity.

The toothbrushes are used to brush fleas from the animals’ fur. Opossums tend to produce the most. Hall said he once brushed 240 fleas from one opossum.

Delayed Results

The fleas are counted and placed in tubes filled with a salt solution. Along with blood samples, the fleas are sent to the Centers for Disease Control in Colorado.

But there is often a six-week wait before the results are returned, Hall said.

“The slow turnaround time has been a thorn in our side,” Fannin said. “We know about things four to six weeks after they happen, but we keep worrying that something is going to happen in that gap.”

She said that the county plans to run the plague tests in its veterinary services laboratory.

In areas where there are signs of infection, such as Agoura, inspectors have also gone door-to-door asking pet owners to have dogs or cats tested. Pets and other animals brought to animal shelters around the area are also frequently tested, Hall said. In 1980, county tests pinpointed a resurgence of plague in the Topanga Canyon area, Hall said.

Adult Education

The plague unit also hopes to teach humans that wild animals can pose a serious health risk, Fannin and Hall said.

“The public should be aware whenever they are in a campground to avoid contact with a wild animal,” Tilzer said. “They should leave domestic pets at home and not set up camp somewhere where a lot of wild animals roam.”

Wild animals should be “treated with respect,” Fannin said. Sightings of dead or dying animals should be reported to health officials, but the animals should not be touched.

Homeowners in rural areas should control ground squirrel populations and all homeowners should report rat problems.

The plague surveillance program in Los Angeles County is regarded as the best in the county, said Barnes of the disease center in Colorado. It gets to the source of the disease before it can jump to humans, he said. But the very factors that make the program work also make it difficult to measure its success.

“With preventive programs like this, you’ve got to believe that you’re doing good,” said Hall. “I feel that we’ve probably saved some lives, but it’s impossible to know for sure.”