- Along with humans, great apes like gorillas and chimpanzees are known to get infected with malaria, but evidence about the parasite’s effects on bonobos has been scant.
- A recent study that analyzed the feces of bonobo across the species’ range found that one bonobo population showed evidence of both malaria infection and a genetic variation that would likely protect them against severe disease.
- This genetic variation was less common in other populations, suggesting that other bonobo groups could be in trouble if climate change brings malaria-carrying mosquitoes into their habitats.
Gorillas and chimpanzees, like humans, have long been known to get infected with malaria. But evidence of the parasite’s effects on bonobos, one of humankind’s closest genetic relatives, has been scant. Now, new research suggests that bonobos do suffer from malaria infection, and that the disease could threaten the survival of some of the species’ wild populations.
An international team of scientists examined bonobo fecal samples collected from the Democratic Republic of Congo (DRC) — the only country where bonobos (Pan paniscus) occur — and stored in the laboratory of virologist Beatrice Hahn at the University of Pennsylvania.
For ten of the sites included in the study, only one fecal sample out of more than 1,400 analyzed tested positive for evidence of malaria parasites. But among a population living on either side of the Lomami River, a major tributary of the Congo River that runs parallel to it in the central DRC, 38% of bonobos had evidence of malaria parasites in their feces.
It wasn’t immediately clear to the researchers what cost the disease has on the Lomami River bonobos, known to the researchers as the TL2 population; telltale signs such as lethargy or reduced reproductive ability are hard to detect in the field. But malaria had evidently exacted a price in the past: the bonobos possessed variants of an immune gene that likely protect them against severe cases of malaria.
“There would have to be a cost for natural selection to favor those immune variants,” said Emily Wroblewski, assistant professor of biological anthropology at Washington University in St. Louis and the lead author of the study documenting the findings.
“This isn’t smoking-gun proof [that malaria is harming bonobos], but it’s proof going in that direction,” she added.
Wroblewski and her colleagues say the protective mechanism against serious strains of malaria among the TL2 bonobos is similar to some human variants. So-called display molecules take digested bits of protein to the surface of cells while they’re still in the liver, and show them to immune cells. If the display molecules happen to capture a bit of protein from a malaria parasite, and the immune cells detect that, the anomaly kicks off the bonobos’ immune system before the parasites enter the bloodstream.
“Basically it’s able to — we think — better alert the immune system to infection in infected cells sooner,” Wroblewski said.
Populations of bonobos further west of the TL2 population were found to possess the same immune variant, but at a much lower frequency. This could leave them vulnerable to more serious malaria infections, such as those that damage the brain and vital organs.
Climate change increases the likelihood of such infections occurring, with changing weather patterns facilitating the spread of malaria-carrying mosquitoes to populations that haven’t had to face the pathogen for a long time.
Should that happen, Wroblewski and her colleagues say that individuals within those populations that possess the immune gene variant, albeit at low frequency, would have a reproductive advantage.
“Hopefully [over time] that would offer some protection for those populations, but we just don’t know,” she said. “Disease is always a huge threat to survivorship and that’s always a concern when it comes to these endangered great apes which are already under so much threat.”
There are currently no reliable figures on overall bonobo numbers, but the IUCN, the global wildlife conservation authority, suggests that hunting and habitat loss could have driven their numbers to as few as 15,000. It’s not clear what kind of toll malaria has taken on the apes; among humans, malaria killed around 619,000 people in 2021, from 247 million infections, according to the WHO.
Martin Surbeck, an associate professor in human evolutionary biology at Harvard University, who was not part of the malaria study, said other diseases also pose a threat to bonobos, including respiratory diseases transmitted by humans.
“What this [latest research] shows is that the health of local human communities and their pathogens should be researched as well, to come up with a One Health approach,” he said, in reference to the concept that recognizes the interconnectedness between humans, animals and their environment.
“It seems to me that these results also hint that more concrete conservation actions should be taken, which protect both human and animal health.”
Wroblewski, E. E., Guethlein, L. A., Anderson, A. G. , Liu, W., Li, Y., Heisel, S. E., … Parham, P. (2023). Malaria-driven adaptation of MHC class I in wild bonobo populations. Nature Communications, 14(1). doi:10.1038/s41467-023-36623-9
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