Plasmodium vivax Relapse Rates Following Plasmodium falciparum Malaria Reflect Previous Transmission Intensity

Abstract

From 2003 through 2009, 687 of 2885 patients (23.8%) treated for Plasmodium falciparum malaria in clinical studies in Myanmar or on the Thailand-Myanmar border had recurrent Plasmodium vivax malaria within 63 days, compared with 18 of 429 patients (4.2%) from 2010 onward (risk ratio [RR], 0.176; 95% confidence interval, .112-.278; P < .0001). Corresponding data from 42 days of follow-up revealed that 820 of 3883 patients (21.1%) had recurrent P. vivax malaria before 2010, compared with 22 of 886 (2.5%) from 2010 onward (RR, 0.117; 95% CI, .077-.177; P < .0001). This 6-fold reduction suggests a recent decline in P. vivax transmission intensity and, thus, a substantial reduction in the proportion of individuals harboring hypnozoites.

Keywords: P. falciparum; P. vivax; Malaria; relapse.

Figure 1.

A, Proportions of acute Plasmodium falciparum malaria episodes that were followed by Plasmodium vivax malaria within 9 weeks in each study, by treatment. Studies of artemether-lumefantrine (AL) and artesunate-pyronaridine (AsPyr) with 6 weeks of follow-up and of artesunate monotherapy (As) with 4 weeks follow-up are also included. Studies of dihydroartemisinin-piperaquine (DP) and artesunate-mefloquine (AsMq) with <9 weeks of follow-up were excluded because shorter durations of follow-up (typically ≤ 6 weeks) with these slowly eliminated drugs miss a substantial proportion of relapses. B, Proportions of acute P. falciparum malaria episodes that were followed by P. vivax malaria within 9 weeks in each study, by location (ie, Myanmar-Thailand border vs elsewhere in Myanmar). AsAq, artesunate-amodiaquine.