Ill chimpanzees search for different plants with medicinal qualities

Some plants that chimpanzees eat when they are sick or injured have been found to have medicinal properties, providing some of the strongest evidence yet that our close relatives self-medicate.

Although there have been reports for decades of chimpanzees using plants to self-medicate, it's difficult to pinpoint when wild animals get sick and what effect their diet may have.

Elodie Freyman Oxford University researchers tracked wild chimpanzees in Uganda's Budongo Forest, recording when they became ill and what they ate. By analysing feces for signs of intestinal parasites and examining urine samples for elevated levels of immune cells, the researchers identified chimpanzees with obvious wounds or intestinal infections.

An analysis of 53 plant extracts ingested by sick or injured chimpanzees found that 88 percent were effective against bacteria pathogenic to humans, including antibiotic-resistant strains like MRSA, and extracts from all species sampled had anti-inflammatory properties.

This systematic approach has allowed the researchers to identify and characterize more species used by chimpanzees than ever before. Kirsty Graham “It's a very impressive project,” said Robert Cole, a researcher at the University of St. Andrews in the UK who was not involved in the work.

Sick chimpanzees would leave the safety of their group to eat certain plants, often choosing plants that were rarely eaten in that area. The rarity of these events makes self-medicating behavior very difficult to observe, but at the same time, it is one of the strongest pieces of evidence that it is a targeted response to illness.

Chimps are typically hesitant to try unfamiliar foods that might be dangerous, Freiman says, so choosing to eat an unusual plant means they have a special reason to do so: “If they're sick, they're not going to stuff their mouths with things that might make them sicker,” she says.

But this doesn't capture everything that's going on, Graham says, because chimpanzee diets are still very diverse. Over generations, a chimpanzee community may be able to overcome this reluctance to new foods if chimpanzees learn from other animals which plants to eat. Simultaneous direct comparisons of the diets of sick and healthy chimpanzees might reveal whether these are active choices, Graham suggests.

Team Members Fabian Schultz Researchers at the Brandenburg University of Applied Sciences in Germany hope that by identifying active compounds in plant extracts, they might uncover promising drug candidates for humans. “What if we could save human lives by following the example of our animal companions?” he says.

In a report released earlier this year, an orangutan, another great ape, was spotted applying plant leaves directly to a wound in an apparent act of self-medication.