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Measuring hidden parasites in falciparum malaria

PLOS



Stages in the life cycle of Plasmodium falciparum (Illustration: Coatney GR, Collins WE, Warren M, Contacos PG (1971) The primate malarias. (Bethesda): U.S. Department of Health, Education and Welfare.)
Click here for full-size image.

A new technique for measuring hidden malaria parasites and assessing severity of disease is described in a paper published on Aug 23rd in PLoS Medicine. Researchers led by Professor Nick White from Mahidol University, Thailand, looked at patients with the most dangerous type of malaria, falciparum malaria. Usually the severity of disease is measured by counting the number of parasites in the blood under the microscope, but this method ignores parasites which are in red blood cells trapped (sequestered) in the capillaries--the smallest blood vessels in the body.

The researchers estimated total amount of malaria parasites in the body by measuring a protein--Histidine-rich protein 2 (PfHRP2)--which is liberated into the blood when malaria-infected red cells spilt. Using this method in 337 patients with varying severity of falciparum malaria they found that the average parasite burden was more than six times higher in patients with severe malaria than in patients hospitalized without signs of severe disease, and was highest in patients who died. This finding fits with current thinking that sequestration of red cells containing the mature forms of the parasite is the most important pathological process in falciparum malaria.

Approximately 40% of the world's population, mostly living in the world's poorest countries, is at risk of malaria. In the tropical and subtropical regions of the world, malaria causes 300 million acute illnesses and at least 1 million deaths annually.

Estimates of plasma PfHRP2 concentrations may be useful as a research tool to assess patients' parasite loads and may also provide one way of assessing the severity of a patient's disease.

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Citation: Dondorp AM, Desakorn V, Pongtavornpinyo W, Sahassananda D, Silamut K, et al. (2005) Estimation of the total parasite biomass in acute falciparum malaria from plasma PfHRP2. PLoS Med 2(8): e204.

CONTACT:
Professor Nicholas White
Mahidol University
420/6 Rajvithi Rd.
Bangkok, Thailand10400
+662-354-9172
+662-354-9169 (fax)
nickw@tropmedres.ac

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