Self-medication in orangutans: Evidence of natural anti-inflammatory agent application

By David Bartholomew @biobartholomew, University of Exeter & former Project Assistant of the Orangutan Health Project.

It was once believed that humans were the only species intelligent and capable enough to use medicine. Since 1978, though, there has been increasing evidence of other animals gaining medicinal benefits from plants, minerals and arthropods. Most notably, self-medication has been identified in all of the great apes, except until recently, in orangutans. A new study in Nature Scientific Reports undertaken by the Orangutan Health Project and University of Exeter has now found evidence of the first example of self-medication in orangutans and the first example of external application of plant material for anti-inflammatory purposes.

The only great ape to live outside of Africa, orangutans inhabit the islands of Sumatra and Borneo in south-east Asia. Since 2003, the Orangutan Health Project, coordinated by Dr. Ivona Foitová, has undertaken studies of orangutan behaviour, documenting everything from their feeding behaviour to their social interactions. Over 10 years, they managed to collect over 20,000 hours of observational data revealing insights into orangutan behaviour that have never been documented before. One such behaviour was the rubbing of leaves from a dragon tree Dracaena cantleyi onto their fur by seven females, all of which were carrying offspring, and one large flanged male. These peculiar observations led Dr. Helen Morrogh-Bernard and her colleagues to investigate the plant’s medicinal properties.

Female orangutans carrying offspring might use the anti-inflammatory properties of Dracaena cantleyi leaves to soothe joint and muscle pain that results from carrying the extra weight of their infant in the canopy. ©David Bartholomew

In the wild, the orangutans were observed chewing the leaves of the dragon tree into a pulp, producing a white soapy lather and then applying it purposefully to their fur for 15-45 minutes. By testing these soapy compounds on cell cultures, it was shown that the leaves contained anti-inflammatory properties, suggesting the orangutans use the plant for self-medication. This behaviour may allow orangutan mothers to relieve pain from carrying their young and for males to nurse wounds following fights.

For years, the local people of Borneo have been using the same leaves to relieve sore muscles and joints. This knowledge was likely obtained from observations of wild animals, revealing the importance of ethno-botany in discovering new plants with potential medicinal properties for both wild animals and humans.

Orangutans are believed to selectively make nests in trees that have anti-mosquito properties, reducing their risk of catching malaria. ©David Bartholomew

Following this study, the Orangutan Health Project is now trying to identify other plants with medicinal properties from observations of wild orangutan behaviour and from local ethno-botanic knowledge. They are also aiming to understand the role of human interactions with orangutans in spreading parasites and the different susceptibility of wild and rehabilitated semi-wild orangutans to diseases. Many semi-wild orangutans are habituated to human presence and readily accept food from tourists and guides in some parts of Indonesia. This could provide a potential transmission route for new diseases to wild orangutans. Comparisons of behavioural data between the two populations may also reveal whether these semi-wild individuals have learnt sufficient skills to undertake self-medicating behaviours to maintain their health. Combined, these findings will be critical in improving rehabilitation efforts, captive orangutan health and ultimately conservation efforts.

To find out more, read the article here.