The P. vivax populations emerging from hypnozoites commonly differ from the populations that caused the acute episode. Activation of heterologous hypnozoite populations is the most common cause of first relapse in patients with vivax malaria.

Cally Roper and colleagues analyze the distribution of sulfadoxine resistance mutations and flanking microsatellite loci to trace the emergence and dispersal of drug-resistant Plasmodium falciparum malaria in Africa.

Parasite clearance data from 18,699 patients with falciparum malaria treated with an artemisinin derivative in areas of low (n=14,539), moderate (n=2077), and high (n=2083) levels of malaria transmission across the world were analyzed to determine the factors that affect clearance rates and identify a simple in vivo screening measure for artemisinin resistance. The main factor affecting parasite clearance time was parasite density on admission. Clearance rates were faster in high-transmission settings and with more effective partner drugs in artemisinin-based combination treatments (ACTs). The result of the malaria blood smear on day 3 (72 h) was a good predictor of subsequent treatment failure and provides a simple screening measure for artemisinin resistance. Artemisinin resistance is highly unlikely if the proportion of patients with parasite densities of <100,000 parasites/microL given the currently recommended 3-day ACT who have a positive smear result on day 3 is <3%; that is, for n patients the observed number with a positive smear result on day 3 does not exceed (n + 60)/24.

Measuring baseline levels of adherence and identifying risk factors for non-adherence are important steps before the introduction of new antimalarials. In Mbarara in southwestern Uganda, we assessed adherence to artemether-lumefantrine (Coartem) in its latest World Health Organization blister formulation. Patients with uncomplicated Plasmodium falciparum malaria were prescribed artemether-lumefantrine and received an explanation of how to take the following five doses at home. A tablet count was made and a questionnaire was completed during a home visit. Among 210 analyzable patients, 21 (10.0%) were definitely or probably non-adherent, whereas 189 (90.0%) were probably adherent. Age group was not associated with adherence. Lack of formal education was the only factor associated with non-adherence after controlling for confounders (odds ratio = 3.1, 95% confidence interval [CI] = 1.1-9.7). Mean lumefantrine blood levels were lower among non-adherent (n = 16) (2.76 microg/mL, 95% CI = 1.06-4.45) than among adherent (n = 171) (3.19 microg/mL, 95% CI = 2.84-3.54) patients, but this difference was not statistically significant. The high adherence to artemether-lumefantrine found in our study suggest that this drug is likely to be very effective in Mbarara provided that patients receive clear dosage explanations.