Scientists at the University of Edinburgh’s School of Biological Sciences and the University of Pennsylvania have solved a century-old mystery about the evolutionary links between malaria parasites and chimpanzees, according to Science Daily.

In what could be a groundbreaking discovery, the scientists found that the parasite P. malariae – one of six species that causes malaria in humans – originated in African apes before evolving to infect people.

The team said malaria caused by P. malariae is often associated with mild disease; however, if untreated, it could cause long-lasting, chronic infections.

The evolutionary mystery has its origins in the 1920s when scientists found chimpanzees infected by parasites that were identical to P. malariae.

It was initially thought that both parasites belonged to the same species. However, until now, this could not be verified as researchers did not study the genetic make-up of the chimpanzee strain.

Now, scientists have used leading-edge techniques to study the parasites’ DNA. They found that there are three distinct species. One species – P. malariae – infects mainly humans, while the other two infect apes.

Of the two ape-infecting parasites, one was found in chimpanzees, gorillas, and bonobos in Central and West Africa, which is only distantly related to the human parasite. But the other ape-infecting parasite is much more closely related to the one that infects humans.

The findings, published in the journal Nature Communications, was funded by the National Institutes of Health, revealed that the human malaria parasite population went through a genetic bottleneck.

The scientists explained that P. malariae was originally an ape parasite but a small number of parasites switched hosts to begin infecting humans.

Lead author Dr. Lindsey Plenderleith said, “Among the six parasites that cause malaria in humans, P. malariae is one of the least well understood. Our findings could provide vital clues on how it became able to infect people, as well as helping scientists gauge if further jumps of ape parasites into humans are likely.”