Question: How was the original malaria parasite formed?

Julian Rayner answered on 13 Mar 2011:

Great question! We think of malaria as a human disease, but actually most vertebrates get malaria – from apes and monkeys to birds and lizards and snakes. All of these are infected by different Plasmodium parasites, and often the parasites that will infect one vertebrate species won’t infect another – we can’t get mouse malaria, for example. So malaria parasites have probably been around for a very long time, and been infecting vertebrates for pretty much as long as they have been vertebrates. Where the original parasite came from is therefore mostly a guess, but there are certain things about the Plasmodium genome sequence that look a little like algae. So our best guess is that the original parasite was a single celled algae that adapted to live inside other cells, instead of living extracellularly on its own. It’s a good way to make a living – there are lots of parasitic cells in the world.

An easier question to answer is how humans first got malaria. This was almost certainly a transmission from apes and monkeys – so a mosquito bit an infected ape, then bit a human a few days later, and passed the infection across. The most deadly form of human malaria, Plasmodium falciparum, almost certainly came from gorillas originally, a discovery that I helped make last year (probably my biggest thrill as a scientist to date).