Chimps, Dirt, and Malaria

National Geographic is reporting on an interesting story about self medicating by eating dirt. Chimps in Uganda’s Kibale National Park have been observed eating dirt. Not just any dirt, though, but a type rich in kaolinite:

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.

Recent research published in Naturwissenschaften suggests a different reason. Chimps also eat Trichilia rubescens. What happens when the two are combined is quite interesting.

From National Geographic:

Eating the bitter vegetation alone gives the chimps no health benefit, researchers say. Instead the plant’s malaria medicine is activated when fine soil particles bind with chemicals in the leaves.


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.”

The researchers tested the idea by grinding up the leaves of Trichilia rubescens and soaking them in a solution that mimiced the digestive juices in the chimp stomach. Then they looked for antimalarial activity. None was observed. They repeated the procedure, this time adding samples of the soil consumed by the chimps. This time the results were positive. In theory the relationship looks good. The one caveat is that this has not been tested in living chimps.


3 Responses

  1. Interesting story.
    The site you link to, though, makes noise. When you go to the site a person from an ad starts speaking to you.
    Shame on National Geographic!

  2. Some browsers offer add-ons, extensions that would block this for you. I went to the page and didn’t have the experience you had, Greg. I was, am mostly running FireFox.
    In this particular instance, I believe the ad you mentioned was blocked by the following:
    – Adblock Filterset.G Updater
    – Adblock Plus
    – Adblock Plus: Element Hiding Helper 1.0.2:
    Internet Explorer 7 now also offers such extensions in a package, a free add-on called Internet Explore Pro, I believe. It’s not, though, yet as robust as the FF stuff noted above.

  3. We eat kaolinite too — it is an additive in food, medicine, and toothpaste plus in cosmetics, natural insect repellent sprays on fruits and vegetables, and other products. Most relevantly, for years kaolinite was the active ingredient in Kaopectate, an anti-diarrhoeal med, before it was replaced by palygorskite and then bismuth subsalicylate. Jared Diamond also writes here about parrots (and humans) eating kaolinite and other micas found in soils because of these minerals’ ability to bind chemically to toxic substances.

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