Malaria species jumps from apes to humans

Malaria is a disease caused by the protozoa of plasmodium species that is transmitted via the infected female Anopheles mosquito. Traditionally, there are four plasmodium species that cause natural human malaria infection: Plasmodium falciparum, Plasmodium vivax, Plasmodium ovale, and Plasmodium malariae.

[Image: Rossche - Long-tailed macaque]

Just four? Not anymore.

Several simian plasmodium species have been reported to be able to infect humans. At least seven species of monkey malaria have been reported as transmissible to man by mosquito bite: Plasmodium cynomolgi, Plasmodium brasilianum, Plasmodium eylesi, Plasmodium knowlesi, Plasmodium inui, Plasmodium schwetzi, and Plasmodium simium. The first known incident occured in 1960, when two laboratory workers became accidentally infected with Plasmodium cynomolgi via an Anopheles mosquito[1].

Plasmodium cynomolgi predominately causes malaria in macaque monkeys but is – as mentioned above - also known to cause experimental and rare natural zoonotic infections in humans. Recently, however, Plasmodium cynomolgi has made the zoonotic jump and started naturally infecting humans[2].

The first naturally acquired human infection with Plasmodium cynomolgi occurred at the start of 2011 in a 39-year-old Malay woman from the east coast of Peninsular Malaysia[3]. Behind her house there is a small, forested area with occasional sightings of long-tailed macaques (Macaca fascicularis).

Since then, there have been another symptomatic infection of a tourist travelling to Malaysia, cases in Malaysian Borneo, two additional Malaysian cases and multiple asymptomatic infections in Cambodia.

The significance of Plasmodium cynomolgi that is transmissible cannot be ignored nor underestimated.

[1] Eyles et al: Vivax-type malaria parasite of macaques transmissible to man in Science – 1960
[2] Bykersma: The New Zoonotic Malaria: Plasmodium cynomolgi in Tropical Medicine and Infectious Diseases – 2021. See here.
[3] Ta et al: First case of a naturally acquired human infection with Plasmodium cynomolgi in Malaria Journal – 2014. See here.