From: Reuters
Published January 18, 2008 03:54 AM

Monkey malaria more widespread in humans: study

HONG KONG (Reuters) - A potentially fatal type of malaria is being commonly misdiagnosed as a more benign form of the disease, putting people at risk, researchers in Malaysia say.

Malaria parasite Plasmodium knowlesi was until recently thought to infect only monkeys, especially long and pig-tailed macaques that are its natural hosts.

But a study of samples taken from more than 1,000 malaria patients in Malaysia between 2001-2006 found that the disease was more widespread in humans than previously thought.

Four of those infected, all from Sarawak, died.


More than a quarter of the patients in Sarawak, on Malaysia's part of Borneo island, were infected with Plasmodium knowlesi, the researchers wrote in the latest issue of Clinical Infectious Diseases journal. A total of 960 of the patients in the sample group were from Sarawak.

"Our finding that P. knowlesi and not P. malariae (benign species) is a significant cause of potentially severe malaria in Malaysia and has important implications for clinical management and control strategies in the local setting, as well as for physicians attending patients," they wrote.

P. knowlesi has the shortest life cycle of all known malaria species, which means it replicates faster than the rest, unleashing a huge number of the parasite inside its victims.

Blood of the four dead patients had high levels of parasites and they had suffered severe abdominal pain, fever and chills.

The researchers said even a short delay in accurate diagnosis and treatment could lead to the rapid onset of complications, including liver and kidney failure.

The parasite is transmitted by a family of mosquitoes that is attracted equally to monkeys and humans. The researchers say the disease is not only restricted to Sarawak, but was present in Sabah, also in Borneo, and Pahang in peninsular Malaysia.

They said the distribution might even be more widespread. Confirmed infections have been found in Thailand and even in China in a worker who had returned from Myanmar.

"Given the evident severity of the illness that it causes, I would recommend that doctors treating patients with a laboratory diagnosis of P. malariae remain alert to the possibility that they may be dealing with the potentially more aggressive P. knowlesi," wrote Janet Cox-Singh at University Malaysia Sarawak's Malaria Research Centre.

"This would be particularly important in patients who have spent time in the forest fringe areas of Southeast Asia where the non-human primate host exists."

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