Medicinal plant use 41Ashfordet al. (1990) in Batwa pygmies and gorillas in Uganda, was not found in the
human samples at Sonso.
Barrows concluded that ‘Although the results show that Budongo’s primates are
infected with a reasonably wide variety of helminths, over the time period of this study
parasite burdens, which in some cases might be considered to be reasonably heavy,
appeared to be well tolerated by chimpanzees.’ This conclusion is borne out by visual
inspection: the majority of the Sonso chimpanzees (there are exceptions such as the
adult male Tinka) have shiny coats and appear to be in very good condition.
Medicinal plant use
The Sonso chimpanzees, like chimpanzees in many parts of Africa,^13 use particular
plants for self-medication, and this may be one way in which they maintain good health
in the face of parasitic infections (Huffman et al. 1996; Huffman 1997, 2001). At Sonso,
a species of Commelinaceaeis used for this purpose:Aneilema aequinoctiale(Fig. 3.2).
This is a herb that grows up to around 1.5 m high on river banks and at roadsides in the
forest. Bakuneeta (pers. comm.) first observed an adult female chimpanzee self-medicating
using the leaves of this species by the side of a logging road that runs northwards
through Budongo Forest from the sawmill. The observation was made early in the morn-
ing. The chimpanzee was taking leaves into its mouth and pressing them in the mouth
rather than chewing them, before swallowing them. He also found whole or part whole
undigested leaves of Aneilemain chimpanzee faeces. Infants learn this behaviour by
close observation of their mothers (Huffman 2001). Since then, other individuals have
been seen self-medicating in the same way.
This herb is not only used in Budongo. Huffman et al.(1996) record it among a
number of plants used by the chimpanzees of Mahale and Kibale. The three samples
described were obtained from faecal samples. The presence of nematode larvae was
noted in the samples with Aneilemaleaves.
Huffman (1997, 2001) notes that all the various species used in self-medication by
chimpanzees, bonobos and lowland gorillas (totalling 35 species as of 2001, found at
sites across the continent) share the characteristic of having leaves covered in trichomes.
We collected leaves of Aneilema aequinoctialefrom Sonso and photographed them
under an electron microscope at Oxford University. Trichomes were indeed present
(see Fig. 3.3).
Huffman suggests that these leaves made rough by trichomes, consisting of material
that does not easily digest, are rapidly passed through the chimpanzee’s intestine and
this physical purge acts to remove the nematodes by excretion with the faeces. Huffman
(2001) includes a picture of a leaf of Aneilema aequinoctialetogether with a worm of
Oesophagostomum stephanostomum; this was one of 20 worms expelled in one dung
sample together with 50 folded Aneilemaleaves.
(^13) Use of such leaves has been reported at 13 sites from Bossou in West Africa right across to Budongo in
East Africa. The majority of these sites are physically isolated from each other.