Captive elephants can spread tuberculosis to humans—'an issue that’s been ignored'

As the coronavirus has heightened public awareness about disease transmission between animals and humans, some experts are warning about the risks of tuberculosis in captive U.S. elephants.

Photograph by Steve Terrill / Jaynes Gallery, Alamy
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Three out of four new or emerging infectious diseases in people come from animals, according to the Centers for Disease Control and Prevention. Some say this makes stopping the spread of tuberculosis among captive elephants more urgent then ever.

Photograph by Steve Terrill / Jaynes Gallery, Alamy

Captive elephants can spread tuberculosis to humans—'an issue that’s been ignored'

As the coronavirus has heightened public awareness about disease transmission between animals and humans, some experts are warning about the risks of tuberculosis in captive U.S. elephants.

Shortly after an emaciated captive elephant named Hattie performed with Circus Vargas, in Southern California, she died in a trailer going to an exotic animal farm in Illinois. Her cause of death, on August 6, 1996, was tuberculosis. Testing revealed that another elephant in Hattie’s circus group also was infected.

In the mid-1990s, after the deaths of several high-profile captive elephants in the United States, veterinarians became aware that the animals had the human strain of tuberculosis (TB). Since then, more than 60 captive elephants—some of which have since died—have been confirmed with the disease, says Susan Mikota, co-founder of Elephant Care International, a U.S.-based nonprofit that provides elephant health-care support. Last year, one elephant was diagnosed with TB at Point Defiance Zoo, in Washington State, and another at Oregon Zoo, in Portland. Today, an estimated 5 to 6 percent of the nearly 400 elephants in U.S. zoos, sanctuaries, and circuses are infected with TB.

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In 1996, days after her last circus performance, Hattie died of tuberculosis. After the deaths of several high-profile captive elephants in the United States in the mid-1990s, veterinarians became aware that the animals could transmit the human strain of TB.

The United States Department of Agriculture (USDA), which enforces the Animal Welfare Act, does not mandate TB testing.

Three out of four new or emerging infectious diseases in humans come from animals, according to the Centers for Disease Control and Prevention (CDC). This makes it important to stop the spread of tuberculosis among captive elephants, says Fleur Dawes, communications director for In Defense of Animals, an animal welfare organization that has campaigned to end the keeping of elephants in captivity.

There are multiple strains of TB—a bacterial infection that spreads through the air and can be transmitted by humans through coughs or sneezes. Infected elephants are thought to spread TB when they spray liquid or air out of their trunks, although no study has confirmed this. Elephants can contract both the human and bovine strains. For both humans and elephants, treatment is a months-long drug regimen.

Because elephants can get the disease from humans, they can transmit it back to us. In fact, 11 of 22 elephant handlers at the Illinois exotic animal farm where Hattie was being transported had positive reactions to a TB skin test in 1996—the first known cases of elephant-to-human TB transmission in the U.S.

Adam Langer, branch chief of surveillance, epidemiology, and outbreak investigations for the CDC, says TB bacteria can stay in the air for several hours, depending on the environment. Exposure risk depends on factors such as the concentration of bacteria in the air, how long the person was exposed, the size of the room, and the ventilation system. While prolonged contact is more likely to cause infection, “it is possible to become infected after a short exposure,” Langer says.

Because elephants are so massive and “have particularly large lungs…they can expel a relatively large number of bacteria into the surrounding air,” Langer says. “Therefore, sharing air space with an elephant with TB can pose a higher risk of becoming infected than the same exposure to a person.” People most at risk are those who spend “considerable amounts of time in an indoor environment with an elephant with infectious TB.” Experts say the danger of transmission to zoo- and circus-goers is low.

Although COVID-19 preoccupies us today, 1.5 million people died of tuberculosis globally in 2018, according to the World Health Organization. That makes it the leading infectious cause of death. (As of September 3, there have been nearly 860,000 reported deaths worldwide due to COVID-19.)

The risk of tuberculosis transmission has been “ignored for far too long,” Dawes says. “Unfortunately, I think it takes something like this pandemic to really put the potential risks into focus.”

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Packy, at Oregon Zoo, in Portland, gets his morning bath. He was euthanized in February 2017 after he developed a drug-resistant strain of TB.

More than two decades after those first cases of elephants infecting people with TB, transmission is still occurring. Last year at Point Defiance Zoo, in Washington State, eight staffers tested positive for a latent, or inactive, form of tuberculosis. They likely contracted the disease from the zoo’s two elephants, Hanako and Suki, who tested positive two months later. In February, Hanako (who also had cancer in her left front foot and advanced joint disease) was euthanized. Suki, elderly at 55, is still alive, but the zoo announced last November that she wouldn’t be treated because the medication could weaken her immune system.

No perfect TB test for elephants

Just as testing humans for COVID-19 has been fraught with difficulties, testing animals as large as elephants for TB is also challenging. Opinions differ over the best methods to use.

Ascertaining whether humans have TB involves taking blood tests and chest x-rays, but it’s impossible to image the lungs of an elephant that may weigh more than 10,000 pounds. “We don’t have x-rays that are strong enough to take pictures of their lungs,” says Michele Miller, the research chair in animal tuberculosis at Stellenbosch University, in South Africa.

Because TB can lie undetected in elephants (and people), it’s possible that apparently healthy animals are infected without anyone knowing, Miller says.

To test elephants, veterinarians have two options: A blood test reveals tuberculosis antibodies but doesn’t necessarily confirm the presence of active disease—instead, it can signal that an elephant had the infection in the past or has latent TB. The other method is a trunk-wash test, which isolates the organism that causes the disease and requires squirting saline solution into the elephant’s trunk, then collecting and analyzing the exhaled liquid for the TB bacterium.

Neither test is perfect, and each can produce false positive or negative results.

The stakes are high when an elephant is infected. Veterinarians take the Hippocratic oath and are sworn to protect human health as well as animal health, so euthanasia may be recommended as a last resort because of the risk an infected elephant may pose to its human caretakers, says Kay Backues, director of animal health at Tulsa Zoo, in Oklahoma.

Treating an elephant for TB is not only costly—up to $60,000—but also may cause serious side effects, such as liver damage and loss of appetite. Moreover, if the test is a false positive, Miller says, “you put that animal through treatment that it didn’t need to have.”

Two tests are better than one

In 2013 at Oregon Zoo, in Portland, a routine trunk-wash sample collected from a 29-year-old bull Asian elephant named Rama tested positive for tuberculosis, even though the elephant hadn’t shown any signs of illness.

Captive elephants regularly have blood drawn, and when a preserved sample of Rama’s blood from May 2012 was analyzed, TB antibodies were found—about a year before his positive trunk-wash test. Two other elephants at the zoo—Rama’s father, Packy, and his brother, Tusko—also had antibodies in their blood. Tusko, it turned out, may have had antibodies as early as 2005.

Packy was later euthanized because he’d developed a drug-resistant strain of TB (as were Rama and Tusko, but for reasons unrelated to TB). In May 2017, four years after Rama’s initial diagnosis, a trunk-wash sample from a female elephant named Shine was positive for TB. The zoo announced that she would receive treatment. Then, in September 2019, they reported that they would begin treating another infected elephant, Chendra, right after she suffered a miscarriage. (The zoo noted that the TB and miscarriage were unrelated.) None of the elephants had appeared sick.

Seven Oregon Zoo staffers and a volunteer also tested positive for a latent tuberculosis infection. The staffers, who were offered treatment, had been in the elephants’ barn or within 15 feet of the animals weekly at least during the previous year; the volunteer, however, had spent only one hour in the elephants’ barn throughout the year. (The volunteer had received treatment by the time news of the outbreak was released.)

Had the zoo relied more heavily on testing the elephants’ blood, Mikota wonders, “would those have maybe been diagnosed earlier?”

Oregon Zoo veterinarian Kelly Flaminio says that may have been the case “if the screening tests that were available in 2012 and 2013 were as effective as the ones we have now.” Early detection of TB in elephants is improving, she says, but “it is still incredibly difficult to definitively diagnose.”

Testing: a matter of choice

What happened at Oregon Zoo shows why it makes sense to use both available tests, says Michele Miller, who co-authored a study on the 2013 Oregon Zoo case. “When you go to the doctor, and you’re not feeling well, they’re going to run a battery of tests,” she says. “The information you get back from a panel of different tests is going to give you a more complete picture of the health of the animal or the person than just one test.”

But testing captive elephants in the U.S. for tuberculosis hasn’t been required since 2015. That’s when the USDA withdrew its policy mandating TB testing as part of standard veterinary care for elephants.

Since then, it’s been left to individual facilities and veterinarians to decide what testing should be done. State health officials regulate the movements of elephants across state lines, and they vary in their strictness and requirements when it comes to TB testing.

Adam Langer, of the CDC, declined to comment on the USDA’s 2015 decision, adding that state and federal regulations “require facilities that house animals (including elephants) to take appropriate measures to protect workers and the public from any potential health or safety hazard posed by the animals in their care.” This requirement covers TB, he says.

According to USDA spokesperson Andre Bell, the agency ended its testing requirement after the United States Animal Health Association, a national nonprofit animal health forum, of which the USDA is a member, “could not agree on an updated version” of the TB testing guidelines the USDA was using. Though many facilities still use the old guidelines, “they are just not required to do so or report the results,” he says. If an elephant is found to have the disease, the USDA has recommended that it not “travel or have public contact” until treatment has been completed.

What risk to the public?

No one can explain how that Oregon Zoo volunteer got infected, says Tulsa Zoo’s Kay Backues, since tuberculosis “is transmitted by close, prolonged, aerosol contact.” Based on what’s known about tuberculosis in humans, watching an elephant from 20 feet away is extremely low-risk, Backues says—and so is walking alongside, or even riding, an elephant. “You get up on its back, you go around the little circle, and you go back—and in a big arena, or a great big expo center, I do not consider that an elephant TB exposure.” It’s not as if you’re standing in front of an elephant “having it blow air into your face.” (Most U.S. facilities have stopped offering elephant rides, but some circuses and unaccredited zoos continue to feature them.)

To date, no documented case exists of TB transmission from a circus, zoo, or sanctuary elephant to patrons.

But an incident at Taronga Zoo, in Sydney, Australia, serves as a cautionary tale about how easily and mysteriously TB can spread, Mikota says. In 2011, a chimpanzee in the zoo was diagnosed with tuberculosis, less than a year after a trunk-wash test showed that a zoo elephant was shedding TB. The chimps’ holding area was about 350 feet from the elephants’ enclosure. That’s “a lot farther than some elephants are from the public,” Mikota says.

“Visiting the zoo or visiting the circus is not a TB risk,” Backues insists.

Mikota acknowledges that there haven’t yet been any known transmissions of TB from captive elephants to members of the public. But because transmission is not well-understood or studied, she believes the possibility is a serious concern. She says only one small study on the Oregon Zoo transmission has been conducted—“hardly enough evidence to say that transmission of TB from elephants to humans is only an occupational health concern versus a public health concern.”

“Absence of evidence is not evidence of absence … [Elephants] can blow out their trunk—wind can take it.”

Wildlife Watch is an investigative reporting project between National Geographic Society and National Geographic Partners focusing on wildlife crime and exploitation. Read more Wildlife Watch stories here, and learn more about National Geographic Society’s nonprofit mission at nationalgeographic.org. Send tips, feedback, and story ideas to NGP.WildlifeWatch@natgeo.com.