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BMJ 2009; 339 doi: (Published 04 August 2009) Cite this as: BMJ 2009;339:b3144

Plasmodium falciparum has become resistant to artemisinin

Artemisinin is the first line treatment of uncomplicated falciparum malaria in areas where malaria is endemic, but evidence is emerging that the parasite is becoming resistant to this drug at the Thai-Cambodian border. This is the site where, in the 1950s and 1960s, resistance to chloroquine and sulfadoxine-pyrimethamine originated, before it spread across Asia and to Africa, contributing to millions of deaths from malaria.

After previous reports of possible artemisinin resistance, two open label randomised trials of 40 patients each, one in Pailin, western Cambodia, and the other in Wang Pha, northwestern Thailand, compared the efficacies of two treatments for uncomplicated falciparum malaria—oral artesunate for seven days, and artesunate for three days followed by two doses of mefloquine.

The trials showed that in vivo susceptibility to artesunate is reduced in Plasmodium falciparum found in Cambodia compared with parasites from Thailand. The median parasite clearance time was 48 hours in Thailand, compared with 84 hours in Cambodia. Rates of recrudescence in the monotherapy and combined groups, respectively, were two of 20 patients and one of 20 in Thailand, and six of 20 and one of 20 in Cambodia. The difference could not be explained by age, pharmacokinetics, in vitro sensitivity tests, or molecular correlates of P falciparum drug resistance.

The authors call for urgent containment measures to limit the spread of resistant parasites.

New approach shows promise for a vaccine against malaria

Immunity against malaria is difficult to achieve, either by natural exposure or by vaccination, and we still don’t know what precisely constitutes antimalarial immunity in humans. Previous attempts to develop a vaccine revolved around the use of irradiated infected mosquitoes; however, a minimum of 1000 mosquito bites over five or more immunisation sessions is needed to induce immunity in volunteers—clearly an inappropriate method for routine use. Some hope comes from the development of subunit …

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