Primates can help us to anticipate the diseases of the future

An international investigation into how diseases are spread amongst primates could help scientists to anticipate outbreaks that may affect humans in the future. Emerging infectious diseases such as SARS and HIV/AIDS are those that have only recently occurred in humans. Such diseases pose a significant threat to global health as humans often lack the natural immunity to fend off infections. Moreover, it takes time for the medical research community to develop effective treatments and vaccines for new diseases.

By learning more about the ways in which diseases spread amongst primates, scientists hope to more effectively predict and prepare for the future diseases that are most likely to threaten humans. Previous research has suggested that humans are most likely to share disease pathogens with the Great Apes – our closest primate relatives. However, the results of the new study, which was conducted by researchers from Trinity College Dublin, Harvard University and Georg-August-Universität, showed that the prevalence of contact between humans and primates also has an important role to play.

Despite being one of our closest relatives, orangutans did not share as many pathogens with humans as had been expected. Conversely, humans shared more than the expected number of disease pathogens with macaques – a more distantly related primate cousin. The researchers believe that such results can be attributed to the fact that orangutans spend much of their time in trees, and so contact with humans is limited.

I spoke to Dr Natalie Cooper, lead author of the study and Assistant Professor at Trinity College Dublin’s School of Natural Sciences, to find out about some of the more surprising findings that she and her colleagues have uncovered. I began by asking Dr Cooper, whose results are due to be published online in the journal Ecology Letters, whether or not she had expected her investigation to corroborate the traditionally held theory that humans share the most pathogens with their closest primate relatives.

"Yes," she replied. "We expected to find that closely related species such as chimps and gorillas would share more pathogens with one another and with humans than more distantly related primates. What we actually found was that we share fewer pathogens than expected with orangutans and more than we expected with Old World monkeys such as macaques and baboons. Even so, humans still share most pathogens with chimps and gorillas – two of our closest relatives."

I asked Dr Cooper at what point it became clear that contact was an important factor in determining the number of disease pathogens that humans share with primates.

"Well at first, we ignored humans," she explained. "Instead, we looked across all primates and tried to determine whether or not more closely related primates shared more pathogens. This approach also enabled us to add other variables. We could account for factors such as the kinds of habitat that different primates inhabited. We discovered not only that it was important for species to be similar in terms of how closely related they were, but also in terms of their ecology and habitat. From here, we surmised that one possible reason behind the odd results that we had obtained was that humans have more contact with some species than they do with others.

"I guess I would say that common ancestry is a really important factor, but it’s not the only factor," continued Dr Cooper. "The implications are that we shouldn’t just be worrying about diseases that might come from chimps, gorillas and orangutans. We should also worry about those that might originate in more distantly related primates, and even within other kinds of species such as rodents and domesticated animals. We might not be very closely related to rats, for example, but we do have a lot of contact with them in domestic situations."

Approximately 60 per cent of emerging diseases are derived from animals. For example, many scientists contend that AIDS is likely to have originated through the hunting and butchering of wild primates in Africa. If researchers can broaden their understanding of how diseases spread amongst primates, therefore, they might be able to better predict and prepare for the outbreaks of the future. Dr Cooper, whose research was funded by Harvard University and the United States’ National Science Foundation, believes that her team’s findings could represent an early step on the road to predicting and pre-emptively acting against emerging diseases.

"This is only the first stage," explained Dr Cooper. "In the future, we hope that researchers will investigate diseases found within Old World monkey populations, but not amongst humans. From here, they can try to work out whether or not these diseases are likely to pass across the human-primate barrier. If such a transition is found to be likely, scientists can start to develop suitable treatments for these diseases."

I concluded our interview by asking Dr Cooper about any further research that she has planned in this area. Does she intend to use these results to predict future diseases that might emerge within human populations?

"Unfortunately, I think that we still have a few more steps to take before we reach this point," answered Dr Cooper. "The first thing that we need to do is to fill in some of the research gaps that we have identified. We have discovered massive gaps where certain types of primate in certain areas simply aren’t being surveyed for diseases. This doesn’t seem to be connected to the likelihood of such diseases being passed to humans. It just appears to be that certain regions are poorly sampled. The first step, therefore, will be to fill these gaps. We need to do this before moving onto the next stage. That is where my research is heading next."