Written by: Jacob Negrey, PhD Candidate, Boston University
Respiratory viruses of human origin infect wild apes across Africa, sometimes lethally. In Uganda, outbreaks of viruses of human origin have been discovered in two different chimpanzee groups. We spoke to Jacob Negrey about the outbreaks and why they happened.
What viruses of human origins are we talking about?
Chimpanzees can be found throughout sub-Saharan Africa, from Senegal in the west to Tanzania and Uganda in the east. There are between 172,700 and 299,700 free-ranging chimpanzees left in the world, about 5,000 of which are in Uganda.
My colleagues and I recently analysed two outbreaks of respiratory disease in two different chimpanzee groups, both located in Uganda’s Kibale National Park.
Large segments of both chimpanzee groups showed signs of disease: 44% of 205 individuals in the first group, which is known as Ngogo, and 69% of 55 individuals in the second, Kanyawara.
Initially, we feared that the same virus caused both outbreaks, which would mean a single virus had been rapidly transmitted throughout the forest. But our team leader, Dr Tony Goldberg of the University of Wisconsin-Madison, tested samples, and we learned that the outbreaks were caused by two different viruses commonly found in humans.
In both cases, we identified viruses of the respiratory tract. In the Ngogo chimpanzees, we found metapneumovirus, which is known to have infected chimpanzees in other parts of sub-Saharan Africa.
At Kanyawara, we found parainfluenza virus 3, which has never before been observed in wild chimpanzees. Various strains of these viruses can be found in humans all over the world, although their full diversity remains poorly understood.
Chimpanzees infected with metapneumovirus and parainfluenza virus 3 showed the same signs of sickness that humans do: Coughing, sneezing, runny nose, lethargy, and weight loss. In humans, these viruses most severely affect infants, children, and the elderly. However, these viruses mostly cause very mild sickness.
In the last 20 years, we have learned a great deal about diseases afflicting wild chimpanzees. For instance, we now know that diseases posing considerable public health concerns for humans, such as Ebola and malaria, are also present in chimpanzees.
We have also learned that humans can easily transmit viruses to chimpanzees and other primates. Our research underscores growing evidence that human-to-ape disease transmission is among the greatest threats to the survival of great apes.
Are these viruses deadly? What’s the impact of this?
The severity of disease varies from virus to virus. While parainfluenza virus doesn’t appear life-threatening, metapneumovirus can be fatal for wild chimpanzees.
At Ngogo, 25 individuals died during an outbreak that lasted for 40 days. When we examined the body of a dead adult female chimpanzee, we found evidence of a sudden and severe infection. Indeed, severe disease from metapneumovirus infection seems much more common in chimpanzees than in humans. This severity may result, in part, because wild chimpanzees have not been previously exposed to these viruses. Because these strains of metapneumovirus and parainfluenza virus 3 originate with humans, wild chimpanzee immune systems are not prepared to fight them.
Furthermore, chimpanzees are slow to reproduce, so outbreaks of lethal disease can greatly reduce population sizes. That has pressing consequences for chimpanzee conservation.
Outbreaks have other devastating consequences for chimpanzee societies. The outbreak in the Ngogo community left several young chimpanzees orphaned, which is emotionally traumatic and may have important developmental consequences.
Are outbreaks of such viruses common in Uganda’s chimpanzees?
Unfortunately, it seems that transmission of human viruses to chimpanzees and other apes, including gorillas, is increasingly common. Last year, my collaborators reported on an outbreak of another common cold virus in Uganda’s Kanyawara chimpanzees. Of the 56 chimpanzees in the community, five died during the outbreak.
If we look at other countries where chimpanzees live, like Côte d’Ivoire, similar cases of human-to-chimpanzee viral transmission have been documented.
We cannot conclusively evaluate how frequently such viral outbreaks occur, because many wild chimpanzee groups are not monitored. We also cannot be certain how the viruses identified in our study were transmitted to chimpanzees – whether directly from humans, or indirectly through another species. However, we know that viral transmission between humans and chimpanzees can happen very easily—perhaps most easily through droplets released when coughing or sneezing.
There are a number of health protocols employed across sub-Saharan Africa to prevent human viruses from entering chimpanzee habitat; these include using hand sanitiser, wearing face-masks, implementing quarantine periods, and maintaining strict distances between humans and chimpanzees. These rules are upheld at research sites but are also important for chimpanzee groups visited by tourists People come from all around the world to view chimpanzees in the wild, and they bring viruses with them, whether they know it or not.
The more we understand about the viruses that endanger apes, and the more conscientious we are about ways disease can be transmitted, the better prepared we will be to protect wild ape populations in the future.
Jacob Negrey's research was funded by the Wenner-Gren Foundation, National Science Foundation USA (Grant Number BCS-1613393), National Geographic Society (Grant Number 9824-15), Nacey Maggioncalda Foundation, and Boston University. Further funding for this research was provided by the National Institute on Aging (Grant Number 5R01AG049395), Leakey Foundation, Horace H. Rackham School of Graduate Studies at the University of Michigan, University of New Mexico, and University of Wisconsin–Madison.