How TB Jumps From Humans to Wildlife -- Vet Seeks Clues

Helen Fields
for National Geographic magazine
February 20, 2009

In ordinary circumstances, Kathleen Alexander would gladly have let her two kids run around the front yard on their own. But during her stint as senior wildlife veterinary officer for Botswana's Department of Wildlife and National Parks from 1995 to 2001, things were not exactly normal. Their front yard was Chobe National Park, a 4,000-square-mile (10,360 square-kilometer) park in northern Botswana with lots of free-ranging wildlife. Alexander always went outside with her children, so they wouldn't get "smushed by an elephant."

But one sunny day in June 2000, she encountered a different problem: two banded mongooses, so thin their ribs stuck out, wandering around the sand pit where the children liked to play. These groundhog-sized animals are common through sub-Saharan Africa, but they run away from humans. Alarmingly, these mongooses weren't afraid of her. "It was clear they were sick," she recalled.

(See more photos.)

Alexander trapped one of the animals and tested it. Her tests revealed it was sick with tuberculosis—the human version. For the first time, free-range wild animals were confirmed to have contracted a human disease.

(For more on non-human strains of tuberculosis read "Lions in South Africa Pressured by TB Outbreak, Hunters.")

It's well known that diseases can—and do—move from animals to people. Avian influenza, which comes from birds, was first confirmed in humans in 1997. But the opposite had never been proven for wild animals, although animals in captivity were sometimes known to get human illnesses.

Tracking TB in Mongooses

Tuberculosis (TB), a highly contagious disease that spreads when an infected person coughs, sneezes, or spits, is a serious problem across southern Africa. Most people in Botswana are infected by the time they are adults. Tuberculosis and HIV often go together; many people with AIDS actually die of TB. The towns of Kasane and Kazungula, next to Chobe National Park, are no exception. Those towns are also infused with wildlife. Warthogs wander the streets and mongooses are common.

Alexander believes mongooses probably pick up the bacteria that cause tuberculosis by nosing around human waste. They like to investigate possible food sources by sticking their noses straight into garbage piles, septic tanks, and sputum. Alexander thinks bacteria get into tiny cuts on their noses, then spread through their bodies. Unlike humans, who can be infected with tuberculosis for years, mongooses appear to sicken and die immediately.

Since that first discovery in 2000, Alexander, who now teaches at Virginia Tech, has been tracking tuberculosis in Chobe National Park's mongooses with support from the National Geographic Society's Committee for Research and Exploration. She hopes to learn more about how the mongooses get infected with tuberculosis and how they fit into the park ecosystem. (National Geographic News is owned by the National Geographic Society.)

Most of the mongooses in the park now sport GPS collars that record their movements. "Following them on foot is just not possible because of all the elephants and lions," Alexander said. She hopes to figure out what they do all day and who their major predators are. Maybe domestic dogs hang out with mongooses in the wild, which would mean they could carry deadly bacteria back to their owners. Or perhaps scavengers like hyenas are getting tuberculosis from mongoose carcasses.

In the meantime, tuberculosis outbreaks among mongooses continue. Alexander has documented five since 2000, and dozens of animals have died. One troop that hangs around a tourist lodge had more than 20 healthy animals eight years ago; after a 2008 outbreak, only seven remain.

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