Abstract

The mountain gorillas in the Virunga Volcanoes of Rwanda, Uganda and Democratic Republic of Congo seem able to tolerate certain species of gastrointestinal parasites without manifesting signs of sickness. Close contact between people and this endangered population is not new, as the fertile Virunga region has supported a high-density human population (up to 400 people/km²) for decades. However, in 1994, as a result of the war and genocide in Rwanda, there was a massive increase of human traffic crossing the park, followed by a military presence. Due to the close genetic relatedness of humans and gorillas there is the possibility of anthropozoonotic disease transmission with potentially devastating consequences for this endangered species.

In 1996–1997, a study carried out in Rwanda by the Mountain Gorilla Veterinary Centre and researchers of University of Tennessee found three intestinal parasites (Trichuris trichiura, Chilomastix sp. and Endolimax nana) not previously identified in habituated gorillas, but known to infect humans. Fecal samples (n=98) were collected from 74 free-ranging gorillas in the Volcanoes National Park with the collaboration of Karisoke Research Center. All samples were examined using centrifugal flotation (zinc sulfate and Sheather’s sugar solutions). Larval cultures were performed to further identify the strongyle eggs seen on flotations. Examination of these samples revealed that 72 of 74 (97%) were infested with strongyles/trichostrongyle-type, 63 of 74 (85%) with Anoplocephala gorillae, 7 of 74 (9%) with Probstmayria sp., one of 74 (1%) with Trichuris trichiura, one of 74 (1%) with a psoroptic mite, and one of 74 (1%) with one unidentified mite. Trichrome stains from 70 of 74 (95%) of gorillas were examined and revealed that 31 of 70 (44%) had Endolimax nana (cysts), 11 of 70 (16%) Iodamoeba buetschlii (trophozoites), 63 of 70 (90%) E. nana and/or I. buetschlii (trophozoites), 31 of 70 (44%) Chilomastix sp. (cysts and trophs), 19 of 70 (27%) Entamoeba hartmanni (cysts and trophozoites), 14 of 70 (20%) Entamoeba coli (cysts and trophozoites), one of 70 (1%) Entamoeba histolytica (trophozoite), and two of 70 (3%) Giardia sp. These newly identified parasites may indicate an increase in contact with human fecal material.

A comparative study is underway in the Virunga National Park, Democratic Republic of Congo, and we may find further evidence of human impact on the gorillas’ health. The Virunga National Park shelters six habituated gorilla groups (about 24% of the gorilla population in the Virunga region).

Pressures on this protected area were enormous after the establishment of two major refugee camps on the edge of the park in 1994. Human presence in the forest has once again increased significantly with the war in the Democratic Republic of the Congo (formerly Zaire) after October 1997, which is potentially disastrous to the gorilla population.

Thus, there is a need to monitor closely the health of the Virunga population. Specifically, we should periodically assess changes in the spectrum of parasites carried by gorillas and variation in parasite loads. This should assist with the control of potential disease outbreaks and provide additional data for the long-term management of this very endangered primate.