Rare human outbreak of monkey malaria detected in Malaysia

Several people in Malaysia have become infected with a species of monkey malaria parasite that, until recently, had been recorded in just one person outside of the lab.

Although only a few cases have been detected, researchers are worried that the ongoing destruction of monkeys’ forest habitat is increasing the amount of contact between people and primates, providing more opportunities for infections to jump to people.

The report was published in the journal Nature.

In January, researchers identified the parasite Plasmodium cynomolgi in five people being treated for malaria in hospitals and clinics around Kapit, a heavily forested area in the centre of the island of Borneo. Although laboratory trials in the United States in the 1960s showed that mosquitoes could transmit the parasite from macaques to humans, researchers had thought that in the wild, P. cynomolgi was transmitted only among macaques. That view changed in 2014, when a study1 re-examined malaria patient samples and found that a Malaysian patient had been infected with P. cynomolgi in 2011.

Malaria specialist Balbir Singh of the University Malaysia Sarawak presented the latest cases at a scientific meeting of the Malaysian Society of Parasitology and Tropical Medicine, held in Kuala Lumpur last month. He says that many more cases of P. cynomolgi in humans might be detected if researchers look for them. Singh was able to detect the cases because his tests used primers — short sequences of targeted DNA — that could distinguish P. cynomolgi from closely related parasites.

The monkey parasite is unlikely to start a public-health emergency, researchers say. It does not seem to cause serious illness in people, and it can be treated with antimalarial drugs, says José Rubio, a malaria scientist at the Carlos III Health Institute in Madrid.

But malaria scientist Bridget Barber, of the Menzies School of Health Research in Darwin, Australia, says that it will be important to determine the prevalence of P. cynomolgi in human populations in other areas and to study if the species can cause severe disease. She says it is too early to comment on the health burden of the parasite.