Parasites belong to the group of pathogens that includes viruses, bacteria, fungi, and prions. Although they have a rather unfortunate reputation, the majority of living organisms are parasitic and they play an important role in orangutan population dynamics and ecosystem diversity. With habitat fragmentation and increasing exposure to human settlements, the dynamic of parasites and their effect on remaining wild orangutan populations are becoming the focus of increasing research (Foitova et. al., 2009).
Parasitic infections can have a devastating impact on the health of any individual, and orangutans, who in some regions suffer prolonged periods of lean fruit availability and decreased nutrition, can be particularly susceptible. Studies have shown there are a number of external factors that influence the susceptibility of populations to parasitic infections, including density, contact with humans and climatic factors which affect temperature and humidity. For example, some species of parasites were found to affect chimpanzees more significantly during periods of higher rainfall, and comparison of parasite levels in Bukit Lawang, a popular tourist destination in Sumatra, and Ketambe, where human contact is low, has found that levels are significantly higher in Bukit Lawang, where several species of pinworm have also been documented (Foitova et. al., 2009).
Research published in 2002 recorded the presence of 10 parasites in 371 fecal samples from 24 wild and semi-wild orangutans, and similar studies in 2005 and 2007 showed similar levels, with 16 parasite species found in 421 samples and 13 parasite species in 376 samples respectively, including Chilomastix mesnelii, Endolimax nana, Balantidium coli, Dientamoeba fragilis, and Entamoeba hartmanni. Variations were found in parasites found most commonly in wild and semi-wild populations, indicating that exposure to humans and outside influences can result in orangutans hosting parasites not typically found in wild populations (Foitova et. al., 2009).
Although this area of research is in its infancy, it is assumed orangutans, like chimpanzees, eat plants containing bioactive substances, which reduce the level of parasitic infections, and orangutans at Sebangu in Borneo have been seen self-medicating (Morrogh-Bernard, 2008).
Foitova, I., Huffman, M.A., Wisnu, N. & Olsansky, M. (2009). Parasites and their impacts on orangutan health. In Wich, S.A., Atmoko, S.S.U., Setia T.M. & Van Schaik, C.P., editors, Orangutans: Geographic variation in Behavioral Ecology and Conservation, Oxford University Press, UK.
Morrogh-Bernard, H. (2008). Fur-rubbing as a form of self-medication in Pongo pygmaeus. International Journal of Primatology, 29, pp. 1059-1064.