Determining the Human Diseases Transmissible to the Great Apes of Western Uganda
IAAAM 2000
Jonathan M. Sleeman, MA, VetMB, MRCVS; Matthew B. Rooney, BA, DVM
Colorado State University, College of Veterinary Medicine and Biomedical Sciences, Department of Clinical Sciences, Veterinary Teaching Hospital, Fort Collins, CO, USA


Uganda is home to two subspecies of great apes. There are an estimated 3000-4000 chimpanzees (Pan troglodytes schweinfurthii) in twelve isolated forest blocks across western Uganda.3 The mountain gorilla (Gorilla gorilla beringei) is restricted in its distribution to two small populations in Uganda: one of approximately 300 individuals in the Bwindi Impenetrable Forest National Park, and the other population of 45 animals in Mgahinga National Park that is continuous with the rest of the Virunga population.8

Due to the close genetic relationship of nonhuman primates and humans, there exists a high potential for the transmission of diseases from humans to great apes.7 The habituation of mountain gorillas and chimpanzees for tourism and research has increased contact with humans. In addition, habituation has altered the behavior of the mountain gorillas such that more time is spent foraging outside the park.4 Uganda has a burgeoning human population that is projected to increase from 21 million to 32 million by 2015.1 Southwestern Uganda, which contains the two mountain gorilla populations, is in an area of particularly high human population density (300 people/km2). These factors will increase pressure on the parks for conversion to agricultural land and increase human encroachment into the forests for harvesting of forest products further increasing human contact with chimpanzees and gorillas. The transmission of an infectious disease from humans to these great ape populations could be regarded as one of the biggest threats to the survival of these species, particularly as the introduction of a novel pathogen to an immunologically naive population would result in greater morbidity and mortality.5

To determine the most common potential anthropozoonotic diseases and estimate the degree of risk for transmission from the local human population, a review of all the outpatient diagnoses made in 1997 by local hospitals in the western districts of Uganda containing great ape populations was performed in May-July 1998. Data were accessed from the Ugandan Ministry of Health's Health Monitoring Information System, the Institute of Public Health, Makerere University, and from district medical offices. Data were not available from two districts that contain chimpanzees. Diagnoses were classified according to World Health Organization guidelines, and a disease was determined to be anthropozoonotic based on available literature.2,7 Results revealed that in 1997, 2.93 million outpatient diagnoses were made in the 13 western districts studied, representing a human population of over 5.24 million people.1 Of all the diagnoses made, between 68.2% and 79.4% (mean for all districts = 73.2%) were the result of an infection that could be transmitted to the great apes. This review identified malaria, respiratory tract infections, intestinal parasites, diarrheas (dysentery, acute and persistent), skin disorders, measles, tuberculosis and occasionally poliomyelitis as the most likely types of anthropozoonotic diseases (Table 1). However, a recent study indicates that human malaria is unlikely to be transmitted to African great apes.6

This knowledge is important in fully assessing the risks, and can be used to derive appropriate measures to prevent disease transmission. In addition, it provides the local health authorities, donors and policy makers with information that should help to improve the human health in the region through appropriate public health measures such as vaccination campaigns. Some of these measures may be as simple as improved sanitation by providing or increasing the number of properly constructed pit latrines in the villages close to forest, or even within the forest areas that have a high level of human activity. Further studies which are necessary to determine more precisely the types and prevalence of anthropozoonotic diseases, and include medical questionnaire surveys of the local population living in close proximity to two forest blocks containing great apes, have been initiated.

In conclusion, there appears to be a high prevalence of infectious diseases in the human population that could be transmitted to the great apes of the same region. The anthropozoonotic potential of these diseases should be more fully evaluated and measures to mitigate the impact of human contact with great apes should be devised. The Ugandan government's Health Monitoring Information System can be useful in monitoring disease trends in the local human population, and serve as a warning system for detecting potential disease threats to the gorillas and chimpanzees. This study illustrates that human and wildlife health are interconnected, and there is a need for a multidisciplinary approach to safeguard the health of both.

Table 1. Selected outpatient diagnoses for 13 western districts of Uganda for the period January 1997 to December 1997.

These diagnoses were considered the most likely diseases transmissible from humans to chimpanzees and gorillas of the same region.



(% of all diagnoses)




Respiratory tract infections



Intestinal parasites






Skin disorders










(2,717 from one district)


a. Recent study indicates that human malaria is probably not transmissible to African great apes.


This study was funded by Colorado State University, College of Veterinary Medicine and Biomedical Sciences and the Center for Conservation Medicine, Tufts University School of Veterinary Medicine. We thank the following persons for assistance with this study: Dr. Alex Opio, Dr. Henry Wamani, Mr. Semujja Lubowa, Dr. Katungu, and Dr. Kabagambe, Ministry of Health, Republic of Uganda; Dr. Fred Wabwire-Mangen, Dr. Margaret Lamunu, and Dr. Henry Serwadda, Institute of Public Health, Makerere University; Dr. Gladys Kalema, Uganda Wildlife Authority; and Ms. Debby Cox, Jane Goodall Institute.


1.  Anonymous. 1997. Statistical abstract. Ministry of Planning and Economic Development, Republic of Uganda.

2.  Brack M. 1987. Agents transmissible from simians to man. Springer-Verlag, Berlin.

3.  Edroma E, N Rosen, P Miller. 1997. Conserving the Chimpanzees of Uganda. Population and Habitat Viability Assessment for Pan troglodytes schweinfurthii. Entebbe, Uganda. Conservation Breeding Specialist Group, Apple Valley, Minnesota.

4.  Goldsmith M. In preparation. A preliminary look at the effects of ecotourism on gorilla behavioral ecology. Am. J. Primatol.

5.  McCallum H, A Dobson. 1995. Detecting disease and parasite threats to endangered species and ecosystems. Trends in Ecol. and Evol. 10: 190-194.

6.  Ollomo B, S Karch, P Bureau, N Elissa, AJ Georges, P Millet. 1997. Lack of malaria parasite transmission between apes and humans in Gabon. Am. J. Trop. Med. Hyg. 56: 440-445.

7.  Ott-Joslin JE. 1993. Zoonotic diseases of nonhuman primates. In: M.E. Fowler (ed.): Zoo and Wild Animal Medicine Current Therapy 3. W.B. Saunders Co., Philadelphia, Pennsylvania, Pp. 358-373.

8.  Werikhe S, L Macfie, N Rosen, P Miller. 1997. Can the mountain gorilla survive? Population and Habitat Viability Assessment for Gorilla gorilla beringei. Kampala, Uganda. Conservation Breeding Specialist Group, Apple Valley, Minnesota.

Speaker Information
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Jonathan M. Sleeman, MA, VetMB, MRCVS

Matthew B. Rooney, BA, DVM

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