Infection Across Species

In 1996, human tuberculosis, one of the leading infectious diseases in the world, was found in two circus elephants traveling through Los Angeles County.

The discovery alarmed veterinarians and sparked a wave of research that now indicates that the cases were more of a trend than a fluke.

Since then, 18 cases have been found, including four in California. This has prompted researchers to conclude that the human tuberculosis bacterium, Mycobacterium tuberculosis, is emerging as a threat to North America’s aging Asian elephants, a species already inching toward extinction in the wild because of its increasing proximity to man.

The cases, which involved about 3.3% of the captive population, also are a vivid example of how a human disease can be transmitted to animals.

Some diseases, such as rabies and certain types of influenza, have been known to jump between animals and humans, according to Dr. Richard Montali, the chief veterinary pathologist at the Smithsonian National Zoological Park in Washington, D.C.

As for human TB, though it has been found in a range of species, it is not common for it to be transmitted to elephants.

The two elephants in 1996 had been coughing, and one had lost hundreds of pounds, both classic signs of the disease, said Dr. C. Patrick Ryan, a veterinarian most recently with the Department of Health Services in Los Angeles County, where one of the elephants died. The second elephant died on the trip home to Illinois.

Researchers think many of the infected animals were exposed in their Asian homelands, where most were born, or while in close contact with infected handlers in zoos and circuses in North America.

“The elephants got it from humans somewhere along the line,” said Dr. Susan Mikota, a veterinarian with the Audubon Center for Research of Endangered Species in New Orleans.

Using DNA fingerprinting, scientists at the U.S. Department of Agriculture have identified five distinct strains of human tuberculosis in eight different elephant groups in California, Illinois, Arkansas, Florida and Missouri.

The USDA recommends that elephants with the active disease be treated with the same drugs used on humans. Treatment costs about $50,000 per animal and is recommended for at least a year. The researchers’ findings appeared in a recent issue of the journal Zoo Biology.

The review paper was authored by Mikota, Montali and Dr. R. Scott Larsen, a veterinarian at North Carolina State University in Raleigh.

Most of the infected elephants have been privately owned--by circuses, concessionaires and others, Mikota said. Four cases have been diagnosed in zoo elephants, including one at the Los Angeles Zoo and another at the San Francisco Zoo.

Risk Greatest for Elephants’ Handlers

The disease may be more prevalent in performing animals because of their mobility, she said. There has been contact between the elephants in the eight groups affected; researchers at this point don’t know if the infected animals are transmitting the disease back to humans.

“It is more of a movement issue rather than a facilities issue,” Mikota said.

Tuberculosis is not an easy bug to catch and it is not transmitted by casual contact. However, elephants typically greet one another by breathing into each other’s trunks and often solicit a similar greeting from their keepers. Handlers, therefore, are considered at the greatest risk, Mikota said. Spectators typically are not close to circus and zoo elephants long enough to be considered at serious risk.

Human TB “is pretty contagious under the right conditions with people,” Montali said. “And there are great degrees of susceptibility among a whole span of mammals.”

It has been found in a range of animals, from nonhuman primates to parrots, he said. “It may have evolved in elephants over the years with their close exposure to man.”

Human tuberculosis is rarely found among African elephants and has not been identified in elephants in the wild, which leads researchers to believe it primarily is a human disease and elephants are accidental hosts.

“I’m much more concerned about people bringing tuberculosis to elephants than elephants giving tuberculosis to people,” said Dr. William Lindsay, director of veterinary care for Ringling Bros. and Barnum & Bailey Circus, which owns about 70 Asian elephants, the largest group in North America. Eight elephants at Ringling’s Center for Elephant Conservation, a breeding farm in Polk County, Fla., and its retirement center in Williston, Fla., have been diagnosed with human tuberculosis, Lindsay said

Tuberculosis, a potentially fatal disease that initially attacks the lungs, spreads through the air, usually when an infected individual coughs or sneezes. From the lungs, the bacteria can move through the bloodstream to other parts of the body, such as the kidneys, spine and brain. However, most infected individuals never develop the disease, and the organism can remain inactive for a lifetime, said Montali, the Smithsonian pathologist.

There were 17,531 human cases reported in the United States last year, according to the Centers for Disease Control and Prevention, 3,606 of those in California.

Worldwide, Asian elephants are considered endangered and are rarely imported into the U.S. Their wild population has plunged to about 40,000 from more than 100,000 in 1900, mainly because of conflicts with man, with whom the elephants compete for land. About 285 live in captivity in North America today.

Today’s tuberculosis cases are not unprecedented. The disease was described in elephants more than 2,000 years ago, and cases were reported intermittently throughout the 20th century, Mikota said. However, it was not until 1998 that the USDA established guidelines requiring all elephants to be screened yearly for the disease, and treatment protocols were set up. The guidelines also recommended that handlers be tested yearly.

Treatment, however, has been a challenge. Some animals must be trained to accept medication orally and rectally; all must be able to tolerate the frequent testing and collection of blood samples to determine drug levels.

Dosage Difficult to Determine

Calle, an Asian elephant transferred to the San Francisco Zoo from the Los Angeles Zoo, was diagnosed in 1997, before the USDA guidelines were in place. (Tuberculosis was found in another elephant that died at the Los Angeles Zoo in 1997.)

Calle was treated with human drugs--isoniazid, rifampin, pyrazinamide--in doses based on the formula used to treat people, said Dr. Freeland Dunker, zoo veterinarian. However, animals absorb drugs differently than humans, and the dosages had to be adjusted and readjusted. “It took six months and 21 formulations until we found something that would be absorbed,” Dunker said. But soon the pills made Calle sick, and she refused to take the medicine.

A Berkeley pharmacist concocted two-pound cocoa-butter suppositories in which to plant the powdered drugs, Dunker said. It did the trick. It ended up costing about $72,000 to treat Calle, not including personnel expenses, he said.

Some elephants have been asymptomatic. Others have shown signs of chronic weight loss or diminished appetites, or have developed coughs or an intolerance to exercise.

With so few cases nationwide, “we can develop trends and ideas about how this works,” Montali said. “But epidemiologically we’re just beginning to understand it. “We’re not at the point where we can draw conclusions, but the learning curve is going up rapidly.”