Why do zoo apes get heart disease

The patient, a 25-year-old male named Dylan, is lying on a makeshift straw-bale bed. He has pads on his chest picking up his heart's electrical activity. A tube down his throat is supplying him with anaesthetic gas and oxygen. The room is basic; bare brick walls and a tiled floor. But the most modern of medical equipment is capturing the image and sound of his beating heart. But this is not a hospital, it is a zoo; Dylan is a chimpanzee. Vets and scientists at Chester Zoo are scanning Dylan's heart as part of a global project to find out how a zoo life affects great apes. Many of humans' closest cousins that are kept in captivity suffer from heart disease. Vets think that zoo life may mimic the sedentary, easy modern life in humans that is also linked to cardiac problems. But only a systematic examination of captive apes will reveal the underlying cause. Couch potato apes? "Ever since the middle of the 20th Century, apes in zoos have been known to have heart problems," explains Steve Unwin, the chief vet at Chester zoo, who is overseeing today's procedure. "What's not known is whether this is a genetic problem - something these animals are predisposed to, or perhaps simply caused by the fact that they live longer in captivity." In captivity, chimpanzees, can survive into their 70s. "But the wild it is harder to gauge," says Steve. "Jane Goodall (the famous British primatologist) studied groups in Gombe with individuals into their 50s, but deaths at a younger age in the wild is more common." The vets also want to find out if the problem lies in how the apes are kept - if zoo life is too sedentary, with a rich diet and too little exercise. "In humans, we might call this couch potato syndrome," he told BBC Nature. The heart health statistics for zoo apes are very similar to those of humans. In the US, more than a third of captive gorillas die of some form of heart disease. The British Heart Foundation estimates that the same conditions claim the lives of about one in three men and women in the UK. Veterinary researchers in US zoos started to look into this more than a decade ago. The team at Zoo Atlanta, led by Hayley Murphy, formalised the study into their Great Ape Heart Project, gathering data from zoos across the US. Dr Murphy has even trained some of the zoo's animals to take part in "awake heart ultrasounds". But the UK team, with the help of colleagues in the US and the Pan African Sanctuary Alliance, are taking the project into a new international phase - setting out to scan every zoo ape they can safely gain access to and, crucially, comparing their heart health with that of wild apes. "There are two main aims of this project," says Steve. "One: to find out what is 'normal' for a chimp, a gorilla, an orangutan [heart]. "The second is to help us prevent cardiac problems [in our apes] before they arise." This is where experts on human cardiac health come in. Apes and athletes The Chester Zoo team is working with sports physiologists, bringing their expertise (and their medical technology) into the research. Robert Shave, professor of sport and exercise physiology at Cardiff Metropolitan University has so far scanned 30 chimps and six gorillas - one enormous 220kg (485lb) male silverback at London Zoo required six men to lift into the examination room. It is, Prof Shave says, early days in the study. But so far they've seen subtle but important differences between human and ape hearts. "The walls of chimps' hearts seems to be slightly thicker, which is what we'd typically see in athletic humans or in humans with cardiac disease." In terms of changes to the heart muscle, heart disease can look a lot like athleticism; when arteries are narrowed or people are overweight, the heart "works harder" and becomes enlarged. The same is true in athletes. "So chimp hearts look like they may be similar to [those of] highly trained athletes," says Prof Shave. He has also recorded differences in the electrical activity of human and apes' hearts, so "normal" heart activity for a human is not necessarily the same as normal in an ape. As the study progresses, Prof Shave and his team will include wild apes in their study, to find out exactly what a healthy ape heart should look and sound like. "We're going to move out to the sanctuaries in Africa, where we can collect data from a large number of animals and understand what is absolutely normal," he explains to BBC Nature. "So, what is normal heart size? What is normal heart function?" When the team have the data that answers those questions, Prof Shave says, they will be able to use it as a "diagnostic tool" for any heart problems in captive apes. At Chester Zoo there have been no signs of heart disease in the chimp group. This, says Steve, could be due in part to the lifestyle and diet of their animals. "As much as possible, [we try to] simulate in captivity what they would do in the wild," he says. That includes giving their chimps sufficient space and cover - or foliage - in their enclosure, allowing them the space and privacy for the "fission/fusion" dynamics of a wild chimpanzee society. "We also have a nutritionist to make sure they get fed properly, so [part of this project] is about educating people too about how these animals should be kept," says Steve. Back in the examination room, next to the chimp enclosure, Dylan is groggily coming round from his anaesthetic. Steve hopes that the chimp's minor medical ordeal will make a major contribution to the health of apes in zoos around the world. "This is a global effort," he says, "to make sure we're looking after our apes as well as we possibly can." As a researcher whose expertise lies in human physiology, Prof Shave is interested in what the comparison between great apes and humans may reveal about our own hearts. "The environmental, nutritional, and physiological demands differ between species and, therefore, it is possible that the cardiovascular system in each of the species may be subtly different, he says. "[So] the comparison between great apes and humans may provide important insight into the way in which the human [heart] has evolved," he said.