Resistant Malaria Increasing on Thailand-Myanmar Border

Increase in artemisinin resistance in P. falciparum from 2001 to 2010; mainly due to parasite genetics

THURSDAY, April 5 (HealthDay News) -- From 2001 to 2010, an increase was seen in artemisinin resistance in Plasmodium falciparum (P. falciparum) on the Thailand-Myanmar border, which was largely attributable to parasite genetics, according to a longitudinal study published online April 5 in The Lancet.

To ascertain whether artemisinin resistance has spread or emerged on the Thailand-Myanmar border, Aung Pyae Phyo, M.D., from Mahidol University in Bangkok, and colleagues measured six-hourly parasite counts in 3,202 patients with uncomplicated hyperparasitemic falciparum malaria who were treated in clinics along the northwestern border of Thailand from 2001 to 2010. Patients were given oral artesunate-containing regimens. Parasites were genotyped and their clearance half-lives were estimated.

From 2001 to 2010, the researchers found that the parasite clearance half-lives lengthened from a geometric mean of 2.6 hours to 3.7 hours, and the proportion of slow-clearing infections increased from 0.6 to 20 percent. In 119 patients in western Cambodia, the mean clearance measured between 2007 and 2010 was 5.5 hours, and 42 percent of the infections were slow-clearing during that time. One hundred forty-eight multilocus parasite genotypes were identified in 1,583 infections that were genotyped; between two and 13 patients were infected with each genotype. There was an increase in the proportion of variation in parasite clearance which was due to parasite genetics, from 30 percent in 2001-2004 to 66 percent in 2007-2010.

"Genetically determined artemisinin resistance in P. falciparum emerged along the Thailand-Myanmar border at least eight years ago and has since increased substantially," the authors write.

One author is co-chairman of the World Health Organization antimalarial treatment guidelines committee.

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