A new study has discovered that chimpanzees can fight off malaria by swallowing mouthfuls of dirt and leaves, which act as 'self-medication' for the animals.
According to a report in National Geographic News, Clay soils consumed by both chimps and humans in Uganda's Kibale National Park contain high concentrations of the mineral kaolinite, a main ingredient in some anti-diarrheal medications.
Experts had previously suggested that chimps ate the fine-grained clay to help ward off intestinal ailments or to obtain added minerals in their diet.
But a French team recently observed that the chimps eat dirt before or after consuming leaves from the Trichilia rubescens plant, which contains potent medicinal chemicals.
According to the researchers, eating the bitter vegetation alone gives the chimps no health benefit. Instead, the plant's malaria medicine is activated when fine soil particles bind with chemicals in the leaves.
'Chimps often select dirt that has been exposed on the roots of newly fallen trees,' said study co-author Sabrina Krief, of the Muséum National d'Histoire Naturelle in Paris. 'This may be to avoid worms, bacteria, and stones,' she explained.
Soil-eating may also provide a soothing coating to the animals' digestive tracts.
Though in humans, soil consumption has often been viewed as a sign of metabolic disorder or even mental illness, the practice is relatively common among animals and is now understood to yield important health benefits.
Like humans, chimps can suffer the potentially fatal effects of malaria, although the types of Plasmodium parasites that cause the disease in chimps are different from the four known to infect people.
In previous laboratory studies, Krief's team had found that extracts of the Trichilia plant were effective in fighting the parasite that causes malaria in chimps.
'I noticed that the chimps often eat soil just before or after eating Trichilia leaves,' Krief said. 'I wondered what might be the effect of mixing the two substances.'
To investigate, Krief and colleagues constructed a laboratory model that duplicated chimpanzees' chewing and digestion.
The researchers ground up leaves and soaked them in an acid solution similar to the chimps' digestive fluids. The mixture was then tested for its ability to kill the malarial parasite.
Solutions of artificially digested leaves without soil showed no anti-malarial activity.
But when samples of the soil consumed by the chimps were added to the mix, the researchers found a strong disease-fighting effect.
According to Jim Moore, an anthropologist at the University of California, San Diego, 'It's been known for a long time that chimpanzees selectively eat certain plants in ways and at times that only really make sense if they are self-medicating.'