The behaviour of free-ranging chimpanzees (Pan troglodytes) has been studied in the Taï National Park in Côte d'Ivoire since 1979. Three communities of chimpanzees have so far been habituated to the presence of humans during this research. As a reaction to an increasing number of disease outbreaks, and consequent deaths, the Taï Chimpanzee Health Project was founded in 2001. This project is a co-operation between the Max Planck Institute for Evolutionary Anthropology in Leipzig and the Robert Koch Institute in Berlin. The interdisciplinary collaboration of behavioural scientists, veterinarians and infectious disease biologists has helped to identify a surprising variety of pathogens such as anthrax, herpes and STLV (Simian T-cell Leukaemia Virus).

On 5 occasions between 1999 and 2006, a respiratory disease broke out among the chimpanzee communities, causing the deaths of at least 21 individuals. In addition to searching for the pathogens responsible for these outbreaks, questions arise as to where the diseases came from: do the pathogens circulate naturally among the chimpanzee population or were they imported?
Systematic studies have lead to the answers to these questions. Tissue samples of tested chimpanzees proved positive for two pathogens typical of respiratory tract infections in humans: the "respiratory syncytial virus" (RSV) and the human metapneumovirus (HMPV). Phylogenetic analyses also showed that the virus strains found in chimpanzees were closely related to pandemic strains currently circulating among human population groups. Hence, the transmission to chimpanzees probably occurred in the not too distant past. Clinical observations and demographic analyses indicate that this is not the first time this type of disease has broken out among the chimpanzees. But this is the first time that direct evidence for viral transmission from humans to apes has been found.
On the other hand, bio-monitoring data collected during our research has demonstrated that research and tourism also have a strong positive effect on the apes as they decrease poaching. The population density of the chimpanzees roaming in the vicinity of areas where research is taking place and in an adjacent tourism area was much higher than in the other areas of the national park. There is no doubt that this protective effect outweighs the chimpanzees' increased mortality caused by the introduction of human pathogens.
To safeguard the future of ape tourism and research, particular attention needs to be paid to a strict adherence to standards of hygiene. Only persons who are vaccinated (for example against measles, mumps and rubella) should be permitted access to the apes. Tourists and researchers alike should only be allowed into the proximity of the animals if they show no symptoms of disease whatsoever. Further, a minimal distance should be kept and the wearing of a mask should be obligatory.

Sophie Köndgen and Fabian Leendertz

Original Publication
_{Köndgen, S., Kühl, H., N'Goran, P. K., Walsh, P. D., Schenk, S., Ernst, N., Biek, R., Formenty, P., Mätz-Rensing, K., Schweiger, B., Junglen, S., Ellerbrok, H., Nitsche, A., Briese, T., Lipkin, W. I., Pauli, G., Boesch, C. & Leendertz, F. H. (2007) Pandemic Human Viruses Cause Decline of Endangered Great Apes. Current Biology 18, 1-5}