How does malaria impact wild African apes?

Malaria is a devastating infectious disease caused by a vector-borne parasite (Plasmodium falciparum) that is carried and transmitted by mosquitoes. In humans, symptoms usually start out mild (fever, chills, and headaches), but the infection can sometimes turn lethal within 24 hours. Although scientists have long been aware that apes can also be infected with this parasite, little has been known about how malaria affects them and how deadly it is. 

Now, a team of researchers led by the Washington University in St. Louis (WUSTL) has found that many species of great apes get malaria and – according to evidence from wild bonobos – the disease appears to harm them too.

“We don’t yet have a good handle on the symptoms and mortality risk,” said study lead author Emily Wroblewski, an assistant professor of Biological Anthropology at WUSTL. “The number of infected animals in captivity that have exhibited disease symptoms has been limited. Sometimes they show symptoms like fever and other things that might be associated with infection, and sometimes not. And in the wild these things are very difficult to track.”

Analyses of DNA in apes’ feces has revealed that malaria is widespread across the geographical ranges of wild chimpanzees and gorillas, with these species of great apes harboring at least 12 Plasmodium species, seven of which are closely related to the parasite causing about 95 percent of human deaths. However, bonobos appeared to have escaped infection in all but two locations where scientists have studied them in the wild. 

This provides experts the opportunity to compare infected populations – in which 38 percent of bonobos had detectable malaria parasites in their feces – to uninfected bonobos from ten other regions across their natural range in the Democratic Republic of Congo, in order to better understand some basic facts about how malaria impacts the health and mortality of great apes.

The scientists discovered that, in areas where the parasite was detected, bonobos were more likely to have particular variants of an immune gene (Papa-B), which are very similar to a human variant (HLA-B*53) that is associated with protection from developing severe and more deadly disease, suggesting that humans and bonobos may share similar immune mechanisms. 

“To us, this means that there is a selective advantage to individuals having these protective variants, because those individuals are more likely to survive their infection and reproduce, causing that variant to rise in frequency,” Wroblewski explained.

“Seeing infected populations differ from uninfected populations in this immune trait suggests that bonobos experience increased mortality or costs to their reproductive success because of their infection. The differences between the bonobo populations provides the first evidence of any kind, albeit indirect, that a wild great ape suffers any sort of consequences from their infection.”

Further research is needed to investigate how this particular immune gene variant protects both bonobos and humans. Better understanding these protective mechanisms could lead to the development of new treatments and vaccines for humans. Moreover, since many great apes are already endangered by anthropogenic factors, clarifying how diseases affect them is important for their future protection.

The study is published in the journal Nature Communications.

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By Andrei Ionescu, Earth.com Staff Writer

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