Rare human outbreak of monkey malaria detected in Malaysia
Handful of people diagnosed with parasite found in
macaques has scientists worried about increasing contact between monkeys
and humans.
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.
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 can 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 study https://www.nature.com/articles/d41586-018-04121-4#ref-CR1" rel="nofollow - 1 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.
Barber suspects that P. cynomolgi infections have been occurring in people for years, but it may be misdiagnosed for another human malaria parasite, Plasmodium vivax, which
looks similar. Routinely-used malaria diagnosis tools such as
microscopy and genetic tests such as polymerase chain reaction may not
be able to distinguish between the two species, she says.
A jump in encounters
P. cynomolgi
is the second species of malaria parasite known to infect both monkeys
and humans in the wild. In 2004, Singh and his team discovered https://www.nature.com/articles/d41586-018-04121-4#ref-CR2" rel="nofollow - 2 that a different monkey parasite, Plasmodium knowlesi, was also causing malaria in humans. Since then, patients infected with P. knowlesi
have been reported all over southeast Asia. In 2013, such casesmade up
57% of malaria infections in Malaysia, and the number of new cases
continues to increase each year. P. knowlesi can cause serious illness if not treated. The five individuals diagnosed with P. cynomolgi were also infected with P. knowlesi, says Singh.
The
rise in monkey-malaria infections among humans comes at a time when
scientists are increasingly concerned about the effect of land clearing
on disease spread. It could be making it easier for some simian
infections to jump between macaques and humans, they say: closer
proximity to macaques increases a person’s chances of getting bitten by
mosquitoes infected with malaria. “Malaria parasites can be promiscuous
in their host specificity,” says Richard Culleton, a malaria scientist
at Nagasaki University in Japan. “They sometimes jump around.”
A 2016 study https://www.nature.com/articles/d41586-018-04121-4#ref-CR3" rel="nofollow - 3 at the northern tip of Borneo found a high incidence of P. knowlesi
among humans in villages that had cleared some of the forest
surrounding them. Study leader Kimberly Fornace, a malaria researcher at
the London School of Hygiene and Tropical Medicine, says macaques moved
closer to human settlements after their forests were felled. They also
found people living closer to macaque habitats. To work out whether
land-use changes have also driven P. cynomolgi transmission to
humans, researchers would have to determine if people with the infection
had traveled to forests where the parasite is found in macaques, says
Fornace.
Although P. cynomolgi infections might not yet
pose a major health concern, researchers say, any new infections make it
harder for public-health officials and governments to eliminate malaria
in these regions. The hosts of P. cynomolgi, long-tailed and pig-tailed macaques (Macaca fascicularis and Macaca nemestrina,
respectively), live across southeast Asia. This complicates efforts to
eradicate malaria, say researchers, because there is a vast reservoir of
the parasite within the monkey population. “We have been fighting
malaria with drugs and bed nets, but we cannot apply these measures on
wild macaques,” says Culleton.
If people are constantly at risk of
exposure to monkey malaria parasites at the fringes of forests, those
areas cannot be considered malaria free, he says. “That becomes a real
problem. And I’m not sure what the solution is.”
Source: https://www.nature.com/articles/d41586-018-04121-4" rel="nofollow - https://www.nature.com/articles/d41586-018-04121-4