The first case of Monkey Malaria occurred in the spring of 1965, when a CIA spy entered the jungles of Malaysia pretending to be a surveyor with the U.S. army.
While the spy, known as B.W., didn’t accomplish much of note he did contract the first known case of monkey malaria.
Upon landing in the United State a Maryland hospital confirmed a diagnosis of Plasmodium knowlesi, a form of malaria previously thought to only infect macaques.
Five decades after B.W. came down with the disease, thousands of P. knowlesi cases have now been reported across Southeast Asia, in every country except Laos. In Malaysia, where the vast majority of cases have occurred, the monkey parasite is now the leading cause of human malaria, accounting for 66 per cent of the country’s 3,923 malaria cases last year, according to government statistics.
Scientists no longer relegate the disease to monkeys, labeling it the “fifth human malaria.”
“It’s surprising how little we do know about P. knowlesi,” stated Jonathan Cox, with the London School of Tropical Medicine and Hygiene. Cox is leading a project that is examining the disease’s emergence. “I don’t think it’s going to cause a pandemic or anything. But we don’t know enough about the risk factors to know exactly what we’re dealing with yet.”
Malaria is caused by the Plasmodium parasite and passed from human to human by mosquito bites. Every year nearly 200 million people in developing countries contract the disease and it kills an estimated 584,000, making it among the most deadly in the world.
Yet there are actually more than 150 species of malaria parasites, but each generally preferrs a specific host. Some like mice, other prefer snakes while still others only infect penguins. Prior to P. knowlesi coming along just four species were known to infect humans.
Scientists have long known that P. knowlesi could infect both monkeys and humans, as for a time patients with neurosyphillis were infected with the parasites as a form of treatment. Yet nobody thought that P. knowlesi infections were happening outside the lab.
Investigations at the time of the first case concluded it was a freak occurrence.
“The 1965 case was probably considered a curiosity,” said Dr. Christopher Plowe, a malaria expert at the University of Maryland. “We had no clue P. knowlesi was significant to human health.”
The husband and wife team of Balbir Singh and Janet Cox-Singh, malaria researchers who moved to Malaysian Borneo, made a startling discovery.
When investigating cases of P. malariae, a rarer and usually milder form of malaria, they found something odd.
Patients were getting really sick and sometimes dying which was highly unusual for P. malariae, which is usually a milder form of the deisease. The Singh team traveled by boat up the Rajang river to where cases were clustering and brought some blood samples back to their lab.
Using brand-new gene sequencing technology, they quickly realized why these cases were so abnormal. They weren’t P. malariae. They were P. knowlesi.
“Initially, we thought it was just one or two cases,” said Singh. “But what we found out was that virtually everything that’s been identified as P. malariae has been P. knowlesi.”
The two malarias look so similar under the microscope that its possible P. malariae hasn’t been in Malaysia for some time and instead its been P. knowlesi.
The big question now becomes understanding how P. knowlesi is being transmitted. Researchers still think that it is sporadically jumping from monkey to human but that raises an interesting, and deadly, possibility: Will it evolve to start spreading human-to-human?
Scientists still have a lot to learn about the new parasite, with a recent study revealing that humans are actually being infected by two subtypes of the parasite.
That brings up another interesting question: What would happen if mosquitoes were simultaneously infected by both P. knowlesi subtypes?
“Potentially you could get hybridization,” said Dr. Cox. “And that might change how pathogenic this parasite is.”