Malaria, P. knowlesi - Asia: background
Date: Wed 9 Sep 2009
Source: BBC News [edited]
<http://news.bbc.co.uk/2/hi/health/8246063.stm>
_Plasmodium knowlesi_ malaria 'poses human threat'
--------------------------------------------------
An emerging new form of malaria poses a deadly threat to humans,
research has shown.
It had been thought the parasite _P. knowlesi_ infected only monkeys.
But it has recently been found to be widespread in humans in
Malaysia, and the latest study confirms that it can kill if not
treated quickly. The work, by an international team, appears in the
journal Clinical Infectious Diseases.
Although the new form of the disease has so far been concentrated in
Southeast Asia, the researchers warn that tourism to the region could
soon see cases appearing in Western countries too.
Malaria kills more than a million people each year. It is caused by
malaria parasites, which are injected into the bloodstream by
infected mosquitoes. Of the 4 species of malaria parasite that often
cause disease in humans, _P. falciparum_, found most commonly in
Africa, is the most deadly. Another parasite, _P. malariae_, found in
tropical and sub-tropical regions across the globe, has symptoms that
are usually less serious.
_P. knowlesi_ had been thought only to infect monkeys, in particular
long-tailed and pig-tailed macaques found in the rainforests of Southeast Asia.
But following work by a team at the University Malaysia Sarawak it
has now been recognised as a significant cause of disease in humans.
The latest study shows that _P. knowlesi_ can easily be confused with
_P. malariae_ under the microscope.
Speedy reproduction
-------------------
However, unlike its cousin, _P. knowlesi_ has the ability to
reproduce every 24 hours in the blood -- meaning infection is
potentially deadly.
Researcher Professor Balbir Singh said this meant early diagnosis and
treatment were crucial.
The researchers carried out tests on over 150 patients admitted to
hospital in Sarawak, Malaysian Borneo, between July 2006 and January
2008 with malaria infection.
They found that _P. knowlesi_ accounted for more than two-thirds of
the infections, resulting in a wide spectrum of disease.
Most cases of infection were uncomplicated and easily treated with
drugs, including chloroquine and primaquine.
However, around 1 in 10 patients had developed complications, such as
breathing difficulties and kidney problems, and 2 died.
Although the fatality rate was just under 2 percent, that made _P.
knowlesi_ as deadly as _P. falciparum_ malaria. The researchers
stress it is hard to determine an accurate fatality rate given the
small number of cases so far studied.
Low platelet count
------------------
All of the _P. knowlesi_ patients had a low blood platelet count,
significantly lower than that usually found for other types of
malaria. However, even though blood platelets are essential for blood
clotting, no cases of excessive bleeding or problems with clotting
were identified.
The researchers believe the low blood platelet count could be used as
a potential way to diagnose _P. knowlesi_ infections.
Professor Singh said: "The increase in tourism in Southeast Asia may
mean that more cases are detected in the future, including in Western
countries. 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."
Source: BBC News [edited]
<http://news.bbc.co.uk/2/hi/health/8246063.stm>
_Plasmodium knowlesi_ malaria 'poses human threat'
--------------------------------------------------
An emerging new form of malaria poses a deadly threat to humans,
research has shown.
It had been thought the parasite _P. knowlesi_ infected only monkeys.
But it has recently been found to be widespread in humans in
Malaysia, and the latest study confirms that it can kill if not
treated quickly. The work, by an international team, appears in the
journal Clinical Infectious Diseases.
Although the new form of the disease has so far been concentrated in
Southeast Asia, the researchers warn that tourism to the region could
soon see cases appearing in Western countries too.
Malaria kills more than a million people each year. It is caused by
malaria parasites, which are injected into the bloodstream by
infected mosquitoes. Of the 4 species of malaria parasite that often
cause disease in humans, _P. falciparum_, found most commonly in
Africa, is the most deadly. Another parasite, _P. malariae_, found in
tropical and sub-tropical regions across the globe, has symptoms that
are usually less serious.
_P. knowlesi_ had been thought only to infect monkeys, in particular
long-tailed and pig-tailed macaques found in the rainforests of Southeast Asia.
But following work by a team at the University Malaysia Sarawak it
has now been recognised as a significant cause of disease in humans.
The latest study shows that _P. knowlesi_ can easily be confused with
_P. malariae_ under the microscope.
Speedy reproduction
-------------------
However, unlike its cousin, _P. knowlesi_ has the ability to
reproduce every 24 hours in the blood -- meaning infection is
potentially deadly.
Researcher Professor Balbir Singh said this meant early diagnosis and
treatment were crucial.
The researchers carried out tests on over 150 patients admitted to
hospital in Sarawak, Malaysian Borneo, between July 2006 and January
2008 with malaria infection.
They found that _P. knowlesi_ accounted for more than two-thirds of
the infections, resulting in a wide spectrum of disease.
Most cases of infection were uncomplicated and easily treated with
drugs, including chloroquine and primaquine.
However, around 1 in 10 patients had developed complications, such as
breathing difficulties and kidney problems, and 2 died.
Although the fatality rate was just under 2 percent, that made _P.
knowlesi_ as deadly as _P. falciparum_ malaria. The researchers
stress it is hard to determine an accurate fatality rate given the
small number of cases so far studied.
Low platelet count
------------------
All of the _P. knowlesi_ patients had a low blood platelet count,
significantly lower than that usually found for other types of
malaria. However, even though blood platelets are essential for blood
clotting, no cases of excessive bleeding or problems with clotting
were identified.
The researchers believe the low blood platelet count could be used as
a potential way to diagnose _P. knowlesi_ infections.
Professor Singh said: "The increase in tourism in Southeast Asia may
mean that more cases are detected in the future, including in Western
countries. 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."
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