Conservation Concerns
Banded mongooses aren't in danger of going extinct. They live across southern Africa in large numbers. But if a disease can jump from humans to one wild animal, it could do the same with others. A new human disease could be disastrous for an endangered species. That includes a lot of primates. Since they're so closely related to humans, it's not hard for them to get our diseases.
In 1996, scabies, a parasitic skin disease, was found in rare mountain gorillas that live along the border of the Democratic Republic of the Congo and Rwanda. The gorillas are a popular ecotourism attraction and get a lot of visits from researchers and rangers, too. Veterinarians who studied the outbreak concluded that the gorillas probably caught the parasites from humans (although they couldn't rule out the possibility that other animals were the source). One baby gorilla died. A more deadly human disease could wipe out an entire family of gorillas.
Animal diseases in humans have been well documented. Avian flu is a constant worry. Severe acute respiratory syndrome, or SARS, which in 2003 made people around the world flinch at every cough, probably originated in bats. HIV started as a primate virus and, according to the most commonly accepted theory, probably jumped to hunters when they killed, butchered, and ate infected chimpanzees.
It makes perfect sense that diseases would also go the other way, said University of Georgia epidemiologist David Stallknecht: "Humans are really putting a lot of infectious material on the ground, so it's just a no-brainer" that wild animals would sometimes get human illnesses. And not just in Africa—it could happen anywhere animals and people come into contact.
So why had it never been confirmed before Alexander encountered two sick mongooses in Botswana? Probably, Stallknecht said, because no one was looking.
In fact, there are plenty of examples of animals in captivity getting diseases from the humans they spend their days with. Zookeepers who work with primates know to stay home—or wear a face mask—when they have a cold, so their charges don't catch the sniffles.
Contagious diseases are a problem with less closely related animals, too. In 1996, three circus elephants from an Illinois farm died of tuberculosis; the bacteria that infected them was identical to that in the sputum of one of their human handlers who had the disease. Now elephant farmers in the U.S. are required to test the animals every year, checking for tuberculosis bacteria with a procedure called a "trunk wash."
Could Risks Boomerang Back to Humans?
As humans keep moving into wildlife territory for tourism or because of population pressures, they'll probably bring more disease to wild animals, warns Kristine Smith, a wildlife veterinarian who works on global health at the Wildlife Conservation Society. "More and more, some of the last wild places in the planet are heavily bordered by dense communities," she said—in many cases, desperately poor communities with little access to health care, and often no running water or sewers.
Researchers are also concerned that a human disease in wildlife might provide bacteria or viruses with another haven in which to evolve and combine with other pathogens, which could make them more dangerous later. For example, said Alexander, it's possible that tuberculosis could evolve to be more virulent when it enters a new host.
Human disease transmission to wildlife could come back around to hurt humans, too, Smith said. "If they're contracting diseases that we can get, they're going to be spreaders. Someone can give an animal a disease, and someone else can get it."
At this point, no infectious diseases have been shown to jump from humans to wild animals and back again; it may not happen often. Some of the diseases that jump may be relatively harmless to animals, or may not get back to humans at all—but scientists just don't know enough yet about how diseases move around.
Alexander hopes new genetic tests that can detect a long list of pathogens at once will give her and other scientists a an easy way to find human diseases in wildlife and determine their prevalence, leading to a clearer picture. "It seems improbable that every other animal is linked up in terms of pathogen transmission, but we don't give [diseases] to anybody else," she said. She hopes her work will help other wildlife experts and epidemiologists understand how to better protect free-ranging animals from human disease—and ultimately stop them from bringing it into our front yards.
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