Monday, August 3, 2009

Malaria in Cambodia

Researchers recently announced that a strain of malaria parasite in Cambodia has become resistant to "arteminisnin-based drugs". This development "could put millions of lives at risk" (Resistance). "Artemisinin-based combination therapies are the recommended first-line treatments of falciparum malaria in all countries with endemic disease. There are recent concerns that the efficacy of such therapies has declined on the Thai-Cambodian border, historically a site of emerging antimalarial-drug resistance" (Dondorp).

"Choloroquine and sulfadoxine-pyrimethamine resistance in P.falciparum emerged in the late 1950s and 1960s on the Thai-Cambodian border and spread across Asia and then Africa, contributing to millions of deaths from malaria. "Since the first reports of chloroquine-resistant falciparum malaria in southeast Asia and South America...drug-resistant malaria has posed a major problem in malaria control. By the late 1980s, resistance to sulfadoxine-pyrimethamine and to mefloquine was also prevalent on the Thai-Cambodian and Thai-Myanmar (Thai-Burmese) borders, rendering them established multidrug-resistant (MDR) areas" (Wongsrichanalai).

"Artemisinins have been available as monotherapies in western Cambodia for more than 30 years, in a variety of forms and doses, whereas in most countries...they have been a relatively recent introduction." An "extended period of often-suboptimal use, and the genetic background of parasites from this region, might have contributed to the emergence and subsequent spread of these new artemisinin-resistant parasites in western Cambodia." "In contrast, artemisinin derivatives have been used almost exclusively in combination with mefloquine on the Thai-Burmese border, where parasitologic responses to artemisinins remain good, even after 15 years of intensive use" (Dondorp).

The recent study compared patients from Cambodia with those from Thailand. "Researchers (Wellcome Trust-Mahidol University Oxford Tropical Medicine Research Program) discovered that on average "patients in Thailand were clear of malaria parasites within 48 hours" but Cambodian patients averaged 84 hours" (Resistance). "These markedly different parasitologic responses were not explained by differences in age" and "adverse events were mild and did not differ significantly between the two treatment groups" (Dondorp). Dr Arjen Dondorp declared, "Our study suggests that malaria parasites in Cambodia are less susceptible to artemisinin than those in Thailand". Currently, artemisinin is used to "clear the parasites at an early stage, preventing them further maturing and reproducing" (Resistance). Since its introduction, "artemisinin-based combination therapies has reduced the morbidity and mortality associated with malaria" (Dondorp).

However, with the new emergence of resistant malaria parasites, the number of malaria related deaths is expected to rise. "Measures for containment are now urgently needed to limit the spread of these parasites from western Cambodia and to prevent a major threat to current plans for eliminating malaria"(Dondorp). "Sixty percent of Cambodia's landscape poses a malarial risk. One million Cambodians are infected with malaria each year" (Wongsrichanalai). "Malaria remains one of the primary causes of mortality in Cambodia... Sustained efforts through local and national malaria control will be necessary to contain Cambodia's malaria epidemic" (Wongsrichanalai).

Image from Donorp. Graph from comparative study between Cambodia and Thailand, and how well the drugs treat malaria.

Dondorp AM, Nosten F, Yi P, et al. Artemisinin resistance in Plasmodium falciparum malaria. N Engl J Med 2009;361:455-467.
Population Reference Bureau. "Fewer Malaria Cases in Cambodia."
"Resistance to Malaria Drug Reported in Cambodia." US World News. 29 July 2009.
Wongsrichanalai C, Pickard AL, et al. Epidemiology of drug-resistant malaria. 2002 Apr.

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