(HealthDay News) – From 2001–2010, 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, MD, 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 2001–2010. Patients were given oral artesunate-containing regimens. Parasites were genotyped and their clearance half-lives were estimated.
From 2001–2010, the researchers found that the parasite clearance half-lives lengthened from a geometric mean of 2.6 hours–3.7 hours, and the proportion of slow-clearing infections increased from 0.6% to 20%. In 119 patients in western Cambodia, the mean clearance measured between 2007–2010 was 5.5 hours, and 42% 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% in 2001-2004 to 66% 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.