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A mysterious heart bone in chimps points to cardiac disease

  • Chimpanzees and other great apes are widely afflicted by heart disease; three-quarters of chimps that die in captivity have been found to suffer from heart disease, and up to 90% of captive chimps could have it.
  • Using high-resolution 3D imaging, a team of researchers discovered that some chimp hearts contain a tiny bone known as an os cordis.
  • Researchers do not yet know how, or why, the bone forms in chimps, but it appears to be more prevalent in those with heart disease.
  • Researchers hope this finding will help conservationists keep captive chimps healthy, and increase broader knowledge of chimpanzee pathology.

In 2008, a chimpanzee named Dorothy died suddenly due to heart failure at Sanaga-Yong Chimpanzee Rescue in Cameroon. This year, another chimp battling cardiovascular disease, Tojo, died at Twycross Zoo in the U.K. For more than a decade, scientists have puzzled over heart troubles rife in chimps, monitoring those under human custody and analyzing their hearts. Now, the revelation of something startling inside these endangered primates’ hearts could advance chimp health and conservation.

Some chimp hearts contain an unusual bone called an os cordis, according to a paper published in Scientific Reports by researchers from the U.K. The bone is just a few millimeters long, and researchers are not yet sure how it forms. But since it’s more prevalent in chimps with heart disease, the authors believe its discovery provides a marker for this deadly illness and could have a big impact on efforts to boost the species’ welfare and survival.

“It was really a surprise because chimps are well studied,” says corresponding author Catrin Rutland, an anatomy and developmental genetics professor at the University of Nottingham’s School of Veterinary Science and Medicine. “We could see this dense body inside the heart, and immediately I thought, ‘That looks like an os cordis!’”

While it occurs without heart complications in grazing animals, dogs and otters, the os cordis has yet to be found in other apes. Investigations into whether they have it, too, are underway. Groups are collaborating across the world to identify risk factors for heart disorders in apes, allow early diagnosis and treatment, and aid in these species’ protection.

“For many years, great apes have been treated as furry humans with respect to cardiac disease,” says International Primate Heart Project manager Aimee Drane, who was not involved in the study. “This publication highlights species-specific differences.”

1) Micro-computed tomography and image reconstruction show the os cordis within chimp heart tissue. Image by Catrin Rutland.

Maintaining a healthy captive population

Cardiovascular problems widely afflict chimps and other great apes. With the global chimp population as low as 150,000 and declining in the face of habitat loss and hunting, uncovering how chimp hearts work and why they’re vulnerable could be critical to protecting these animals, Rutland says.

“Some conservation techniques are centered around sanctuaries or zoos, where we maintain chimpanzees to reintroduce into the wild,” she says. “To do that, we have to keep them healthy.”

Past research indicated that more than three-quarters of chimps that died in zoos had heart disease. Idiopathic myocardial fibrosis (IMF), a tissue growth associated with cardiac rhythm anomalies and sudden death, is the heart condition that chimps suffer most: it affects up to 90% of ex situ, or captive, individuals.

Rutland and her colleagues harnessed exceptionally high-resolution 3D imaging known as micro-computed tomography to inspect the hearts of 16 chimps that died in European zoos. They detected the os cordis only in the three chimps with pronounced IMF. Although it was the first time ever that these primates’ hearts were examined through this technology, the researchers knew they were observing bone because they’d scanned other bones using the same approach.

“Never did I imagine that we’d find an os cordis,” Rutland says. “We were trying to just get a look at fibrosis because we knew it was a real problem in chimpanzees.”

Drane says the discovery “helps identify abnormalities and classify disease.” It’s important, she says, to conduct broader research into how age, sex, genetics and the conditions of life in captivity are linked to cardiovascular illness in chimps, and to determine whether IMF is a concern for those in the wild.

Study co-author Craig Sturrock stands before the micro-computed tomography technology that revealed the os cordis. Image by Catrin Rutland.

Karen Terio, a pathologist with the Great Ape Heart Project and the Gombe Ecohealth Project, who wasn’t involved with the paper, says that since wild chimpanzees haven’t shown much fibrosis to date, they likely don’t have the heart bone.

“This finding is useful for the ex situ population, and having a robust, healthy ex situ population is important as a safeguard against extinction for a species,” she says. “The question becomes, is this cause or effect, or to what extent is it present? It’s probably a manifestation of heart disease, so we need to figure out what’s causing the fibrosis in the first place.”

The os cordis could impair cardiac electrical signals and raise the likelihood of irregular heartbeat and unexpected mortality, the study authors say. On the other hand, the bone could be an unhealthy heart’s coping mechanism.

“Some suggest that this bone can conduct electricity better than diseased heart tissue, so maybe the body is trying to help the heart keep beating,” Rutland says.

Pinpointing what’s behind cardiovascular issues in chimps will empower conservationists to care for them better in captivity.

“We don’t want to put them back into the wild having eaten the wrong diet, gotten the wrong level of exercise or had the wrong environment,” Rutland says. “That would potentially cause them to have heart disease later.”

Rebeca Atencia, executive director of the Jane Goodall Institute in the Republic of Congo and head vet at the Tchimpounga Chimpanzee Rehabilitation Centre, says stress may contribute to the appearance of the heart bone.

“Chimpanzees are suffering from stress in areas of deforestation,” she says, which is altering their social activities and communities. “If we understand the cardiac situation better, we can put systems in place to reduce stress and increase wellbeing.”

She proposes designating spaces exclusively for chimps, free from human interference.

A trio of wild chimps peers out from the trees in Uganda. Image by Julie Larsen Maher via Flickr (Public domain).

“People haven’t often heard of a bone in the heart, let alone in chimps,” says Rutland, whose team is currently exploring why and how the os cordis forms in chimps and its implications for their cardiovascular functions. “We’re really happy about the increased awareness of chimpanzees and getting children interested. One of my colleagues was at our local zoo and overheard parents saying, ‘Did you know bones have been found in the hearts of chimpanzees?’”

Such new and engaging detailed knowledge can inspire people to help save the species by making environmentally responsible purchases, supporting sustainable food production and fighting deforestation, she says.

For scientists, vets and wildlife managers, Terio says, the os cordis “gives one more piece of information about heart disease in chimpanzees. It’s something we need to be looking for, which gives us an indication of severity and what might be going on.”


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