Malaria: The Gorilla's Gift
Historically, scientists thought that the most severe form of malaria, known as falciparum malaria, first spread into humans from chimps. But now, by looking for the parasitic DNA in faecal samples from thousands of wild apes, including chimpanzees, gorillas and bonobos, Edinburgh University's Paul Sharp and his colleagues have found that, in fact, it was gorillas that gave us malaria rather than chimps. He talked our own Smitha Mundasad through the work, due to be published in Nature this week.
Paul - Before we set out on this particular study, there was one species of Plasmodium known to infect chimpanzees and that's a species called Plasmodium reichenowe which is quite closely related to Plasmodium falciparum - the worst cause of malaria in humans. What we have subsequently found is that there are in fact six similar species of Plasmodium and we found three species of Plasmodium that only infect gorillas. When we compare those different species of ape Plasmodium to the human species, all the evidence suggests that the human Plasmodium has originated by a jump from gorillas to humans.
Smitha - What implications does that have now for our understanding of malaria?
Paul - Well, the initial aspect of this of course is just that it satisfies our curiosity about where humans acquired their Plasmodium parasite from in the first place. But ultimately, it can also prompt us, or others, to ask whether there are any differences between the strains that infect gorillas and that infect humans. For example, it looks like only one of those six species has successfully jumped into humans and it looks like it may have only done it on one occasion. These parasites are transmitted from ape to ape by mosquitoes and we would expect those mosquitoes also to be biting humans who live in close proximity to the apes. So we would expect there have been many opportunities for those Plasmodium parasites to infect humans but most of those occasions, they simply aren't successful. It looks like the gorilla strain that did make it into humans must've undergone some kind of adaptation - it would be really interesting to find out what that was.
Smitha - Could these findings lead in some way to find treatments in the end?
Paul:: Any additional knowledge about what it is about these strains that allow them to infect humans or doesn't allow them to infect humans could lead to insights for therapies. Perhaps the most important implication of the work is that it says that there are these other species of parasites out there that might have the potential to infect humans in the future. And that would be particularly important if people were successful in curing humans of Plasmodium falciparum. There's a possibility that we're simply opening up the niche for one of these other ape parasites to jump into humans.
Smitha - Has this research thrown up any new questions?
Paul - There are all sorts of questions that arise out of this. We never find one of the chimpanzee parasites in faecal samples from gorillas and we never find one of the gorilla parasites in faecal samples from chimps. Presumably there's something about whether these parasites can successfully infect blood samples of other species, and it would certainly be intriguing to figure out - what is that species specificity? And of course, that then leads into the question of whether that specificity could change so that any of those parasites could infect humans in the future.
Smitha - Do you have plans for further research?
Paul - We do hope to look first of all at human samples to see whether any of these other ape species of Plasmodium have made it into humans. We also want to look further at the ape samples because Plasmodium falciparum, although it is the most common form of Plasmodium causing malaria in humans, is only one of four or five different species of Plasmodium that infects humans. We haven't really looked extensively at these ape samples to see whether the apes are infected by relatives of these other Plasmodium species that infect humans.