Human Delivered Parasites Kick Chimps While They're Down

It's no secret that Chimpanzees aren't in the best shape. With their habitats shrinking across the globe, wild populations of chimps total to only about 250,000, earning them an endangered status according to the IUCN Red List. Now new research has found evidence that parasites delivered by humans could be keeping these great apes down despite recovery efforts.

That's at least according to a study recently published in the journal PLOS Neglected Tropical Diseases, which details how a team of researcher visiting Tanzania's Gombe Stream National Park investigated the parasite Cryptosporidium (Crypto) and cross-species transmission risks from humans. The investigated how chimps could pick up the parasite even indirectly form humans, after it was passed from humans to domestic animals to the greater Gombe ecosystem.

"We found that people are likely exposing the endangered chimpanzees of Gombe to a particular species of Cryptosporidium, which may be contributing to their decline," Michele Parsons, a researcher from Emory University, reiterated in a statement. "It appears to be a case of spillover, or exchange of a pathogen, from humans to animals, instead of the other way around."

According to the study, Parsons and her colleague collected fecal samples from a number of chimps, baboons, humans, and domestic animals (both livestock and pets) that frequently interact with the Gombe area. They found Crypto infection rates of about 16 percent in wild primates, 4 percent in humans, and 10 percent the goats and sheep - and that's despite the fact that the chimps were exposed to the parasite through these sources and not the other way around.

So why the dominant infection rate in chimps? The researchers suggest that it's because the vulnerable animals are being assaulted by the parasite from multiple fronts. (Scroll to read on...)

DNA sequencing revealed three subtypes of the parasite in all, one of which is common among humans, while the others likely came from livestock, pets, or pigs specifically.

Baboons have been known to raid human neighborhoods, sifting through trash, while chimps frequently are caught raising agricultural fields where livestock exposure is most likely. When these animals return to the forests of Gombe, they likely are bringing the parasites with them.

So why is that a bad thing? Crypto is already one of the most well-known causes of waterborne disease across the globe, causing moderate-to-severe diarrhea and dehydration in infected humans. In chimps, it can even prove fatal, as great apes infected with simian immunodeficiency virus (SIV), the ancestor of HIV, often live a fraction of their normal lifespan after also being infected with Crypto.

That's why conservationists are calling for action to be taken to help reduce this kind of disease exposure, pointing to data that shows how chimp populations in Gombe have dropped by about 30 percent in the last two decades (from 150 to 100), despite the fact that the region officially became a protected wildlife park all the way back in 1968.

"When it comes to protecting endangered species, the focus is often limited to providing habitat and preventing hunting," Thomas Gillespie, who co-led the study alongside Parsons, explained. " "But disease also matters in conservation, and that's a relatively new message. Our research shows that if we're going to keep these iconic chimpanzees on the planet, we need to address the spread of infectious diseases."

Understanding where these diseases are coming from, he added, is the first step to establish "good baseline data in order to monitor emerging pathogens," and determine how and when to halt thier advance in human and vulnerable animal populations alike.

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