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Researchers Identify Deadly New Malaria Strain

September 9, 2009

New research has shown that an emerging new form of malaria caused by the parasite Plasmodium knowlesi, originally believed to only infect monkeys, also poses a deadly threat to humans, BBC News reported.

It has been found to be widespread in humans in Malaysia and the international team of experts says it can be deadly if it is not quickly treated.

So far the new form of the disease has been concentrated in South East Asia, but researchers warned that Western countries could soon see new cases due to tourism in the Asian region.

P. falciparum, found most commonly in Africa, is the most deadly of the four species of malaria parasite that often cause disease in humans. P. malariae, found in tropical and sub-tropical regions across the globe, has symptoms that are usually less serious.

The researchers wrote in the journal Clinical Infectious Diseases that P. knowlesi had been thought only to infect long-tailed and pig-tailed macaques found in the rainforests of South East Asia, but it has now been recognized as a significant cause of disease in humans, according to the team from the University Malaysia Sarawak.

P. knowlesi can easily be confused with P. malariae under the microscope, the study warned. But P. knowlesi has the ability to reproduce every 24 hours in the blood, which makes any possible infection more lethal.

That means early diagnosis and treatment are crucial, according to researcher Balbir Singh.

Tests on over 150 patients admitted to a hospital in Sarawak, Malaysian Borneo, between July 2006 and January 2008 with malaria infection found that P. knowlesi accounted for over two-thirds of the infections, resulting in a wide spectrum of disease.

While the majority of infection cases were uncomplicated and easily treated with drugs, including chloroquine and primaquine, around one in ten patients had developed complications, such as breathing difficulties and kidney problems.

Two patients even died from the infection. With a fatality rate less than 2 percent, P. knowlesi is considered as deadly as P. falciparum malaria. But researchers noted it was hard to determine an accurate fatality rate since only a small number of cases have been studied so far.

Low blood platelet counts — significantly lower than that usually found for other types of malaria — were found in all of the P. knowlesi patients.

But while blood platelets are essential for blood clotting, no cases of excessive bleeding or problems with clotting were identified.

The low blood platelet count could even be used as a potential way to diagnose P. knowlesi infections, researchers said.

“The increase in tourism in South East Asia may mean that more cases are detected in the future, including in Western countries,” said Singh.

Singh advised that any clinicians assessing a patient who has visited an area with known or possible P. knowlesi transmission should be aware of the diagnosis, clinical manifestations, and rapid and potentially serious course of P. knowlesi malaria.

Malaria, which kills more than a million people each year, is caused by malaria parasites, which are injected into the bloodstream by infected mosquitoes.

Image Caption: Band-form trophozoite of P. knowlesi in a Giemsa-stained thin blood smear from a human patient that traveled to the Philippines.  Image courtesy of the Wadsworth Center, New York State Department of Health.

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