Where did Malaria Come From?

Remember, zoonotic diseases, the ones that have jumped species? Is malaria a zoonotic disease? Nah, you say, it’s a vector-borne disease. The female anopheles mosquito carries it from one host to another. Or is there more to the story, asks David Quammen in his awesome book, Spillover.

 

Then again, there are different types of malaria in humans, birds and monkeys. Which makes this a possibility:

“Because we humans are a relatively new primate, it was always logical to assume that our oldest infectious diseases had come to us – transmogrified at least slightly by mutation - from other animal hosts.”

 

One theory held that malaria took off in humans with the advent of agriculture. It led to dense aggregation of humans, irrigation led to stagnant water around those humans… you get the idea. The idea’s certainly “based on sensible deduction”. Another theory held the domestication of poultry as the transfer point. After all, those birds do have their own form of malaria.

 

Another set of theories are based on genetic forensics. The genetic code of the most virulent malarial parasite in humans seems to be a “twig” in the branch of a very similar virus abundant in chimpanzees. So did it get transferred from chimps to human via a mosquito bite?

 

Another group of scientists then found that the strain of malarial parasites in humans is far closer to that in a species called bonobo, aka pygmy chimpanzee. On the other hand, there could be a different explanation:

“If bonobos carry a form of (pathogen) that is so similar to what humans carry, those parasites may still be passing back and forth between bonobos and us.”

 

Or did it come from gorillas, as other studies find the nearly identical parasite in them and in humans. Or does that just mean the parasite has jumped back and forth across gorillas and humans in recent times?

 

See how hard it is to know for sure? If that’s very unsatisfying, let me end with a “use” for malaria that was found in 1917 by Julius Wagner-Juaregg. In that pre-antibiotic era, syphilis was a very painful disease. Wagner-Juaregg found that the bacteria causing syphilis “didn’t survive in a test tube at temperatures much above 98.6 degrees F”. Ergo, with “cold logic – revise that, hot logic”, he came up with the idea of “pyrotherapy”. Deliberately infect the syphilis patient with malaria. Their temperature would spike and “you might cook the bacteria to death”. Then cure them from the malaria with quinine!

 

It seems humans can weaponize anything, including diseases.