You can give your cat the flu. You can also pass pneumonia to a chimpanzee or tuberculosis to a bird. This kind of human-to-animal disease transmission, known as reverse zoonosis, has been seen on every continent except one: Antarctica. Now, human-linked pathogens in bird poop reveal, for the first time, that even animals on this isolated, ice-bound landmass can pick up a bug from tourists or visiting scientists. This newly identified infection route could have devastating consequences for Antarctic bird colonies, including population collapse and even extinction.
“[We’re] obsessed about the potential for novel diseases to jump from wildlife to humans and cause an epidemic,” says ornithologist and ecologist Kyle Elliott at McGill University in Montreal, Canada, who was not involved in the new study. “In reality, the transmission of novel diseases from humans to wildlife has been far more disastrous.”
The list of diseases that animals pass on to humans is long: anthrax, Ebola, tuberculosis, and Zika, to name just a few. By contrast, diseases known to move exclusively from humans to animals is much shorter, including human strains of influenza and mumps. Some pathogens—like Salmonella and Campylobacter—bounce from animal to human and back again. But some strains are specific to people, and simple blood tests can determine whether a pathogen started out in an animal or a human host.
Microbiologist Marta Cerdà-Cuéllar at the Research Center for Animal Health in Barcelona, Spain, was skeptical of a mainstream scientific idea—that reverse zoonosis doesn’t exist in Antarctica. So she and colleagues collected fecal samples from 666 adult birds from 24 different species throughout the Southern Ocean, including rockhopper penguins, Atlantic yellow-nosed albatrosses, giant petrels, and skuas. Fearing that already deposited waste might be contaminated, the scientists scooped their poop from the birds themselves, a tricky business that meant catching them and cleaning them out with sterile swabs.
“Penguins are very strong … and skuas are extremely clever,” says Jacob González-Solís, an environmental and evolutionary biologist from the University of Barcelona who was on the team. If you fail to catch a skua during your first approach, he says, it will never let you get close again.
They collected their samples from 2008 to 2011 at four locations: Livingston Island, off the Antarctic Peninsula; and the Southern Ocean outposts of Marion Island, Gough Island, and the Falkland Islands, which are on many of the seabirds’ migration routes. Birds and humans in the more isolated islands are coming into increasing contact, thanks to research centers there and growing numbers of tourists.
From the fecal samples, the scientists isolated and identified bacterial species and compared them to strains in humans and domestic animals. DNA from Campylobacter jejuni, which causes food poisoning, was a close match for such strains, suggesting humans may be passing their bacteria on to local seabirds, the researchers report online in Science of the Total Environment. The presence of certain strains of Salmonella and an antimicrobial-resistant type of another gastrointestinal bug, C. lari, which was found in all four locations, supports that conclusion, Cerdà-Cuéllar says.
Elliott says it’s hard to predict which species will be impacted by the spread of these microbes. “We often think of polar environments as being too cold and that disease transmission is not a huge threat, but the authors have clear evidence that … bacteria can spread widely in polar environments.” González-Solís predicts that, even though Salmonella and Campylobacter don’t kill most infected wildlife, the pathogens could have “devastating” consequences to Antarctic bird colonies, because this is the first time most birds there have been exposed to these strains.
So, say the paper’s authors, governments and scientific organizations need to do more to limit human impacts in Antarctica. For example, they should enforce existing rules about carrying home human waste—which can spread bacteria—says marine and polar ecologist Thomas Brey of the Alfred Wegener Institute in Bremerhaven, Germany, who is the German representative to the Scientific Committee of the Commission for the Conservation of Antarctic Marine Living Resources.
Elliott is pessimistic. “One reason that Antarctica remains largely protected is because of lobbying from tourist and scientific groups,” he says. “While we should do as much as possible to reduce transmission, it’s hard to believe that we will stop tourism and science at these sites, and so it is hard to believe that humans won’t continue to transmit pathogens.”