Single dose primaquine to reduce gametocyte carriage and <i>Plasmodium falciparum</i> transmission in Cambodia: An open-label randomized trial

<div><p>Background</p><p>Single low dose primaquine (SLD PQ, 0.25mg/kg) is recommended in combination with artemisinin-based combination therapy (ACT) as a gametocytocide to prevent <i>Plasmodium falciparum</i> transmission in areas threatened by artemisinin resistance. To date, no randomized controlled trials have measured primaquine’s effect on infectiousness to Anopheline mosquitoes in Southeast Asia.</p><p>Methods</p><p>Cambodian adults with uncomplicated falciparum malaria were randomized to receive a single 45mg dose of primaquine (equivalent to three SLD PQ) or no primaquine after the third dose of dihydroartemisin-piperaquine (DHP) therapy. A membrane-feeding assay measured infectiousness to <i>Anopheles dirus</i> on days 0, 3, 7, and 14 of blood-stage therapy. Gametocytemia was evaluated by microscopy and reverse-transcriptase PCR.</p><p>Results</p><p>Prior to trial halt for poor DHP treatment efficacy, 101 participants were randomized and 50 received primaquine. Overall microscopic gametocyte prevalence was low (9%), but gametocytemic subjects given primaquine were gametocyte-free by day 14, and significantly less likely to harbor gametocytes by day 7 compared to those treated with DHP-alone, who remained gametocytemic for a median of two weeks. Only one infectious subject was randomized to the primaquine group, precluding assessment of transmission-blocking efficacy. However, he showed a two-fold reduction in oocyst density of infected mosquitoes less than 24 hours after primaquine dosing. In the DHP-alone group, four subjects remained infectious through day 14, infecting roughly the same number of mosquitoes pre and post-treatment. Overall, microscopic gametocytemia was an excellent predictor of infectiousness, and performed better than submicroscopic gametocytemia post-treatment, with none of 474 mosquitoes infected post-treatment arising from submicroscopic gametocytes.</p><p>Conclusions</p><p>In a setting of established ACT resistance, a single dose of 45mg primaquine added to DHP rapidly and significantly reduced gametocytemia, while DHP-alone failed to reduce gametocytemia and prevent malaria transmission to mosquitoes. Continued efforts to make single dose primaquine widely available are needed to help achieve malaria elimination.</p></div

Baseline characteristics of study subjects.

<p>Baseline characteristics of study subjects.</p

Infectiousness to mosquitoes during follow-up.

<p>Infectiousness to mosquitoes during follow-up.</p

Gametocytemia and mosquito infection among infectious patients.

<p>Gametocytemia and mosquito infection among infectious patients.</p

Relationship of microscopic gametocytemia to prevalence of mosquito infection.

<p>The results of 35 membrane feeding assays performed on gametocytemic blood from 14 subjects pre and post-treatment. Black circles denote assays performed pre-treatment (Day 0), while colored squares denote assays performed post-treatment (Days 3, 7, 14) on subjects in the DHP-only group (indigo) and subjects in the DHP+PQ group (green). Additionally, the only two mosquito infections observed to arise from submicroscopic gametocytemia (pre-treatment) are depicted on the y-axis. Raw data for infected mosquitoes is available in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0168702#pone.0168702.t003" target="_blank">Table 3</a>. Note pre-treatment data (black circles) were previously presented in Ref 18.</p

Gametocyte prevalence during 42-day follow-up.

<p>Gametocyte prevalence for each regimen, as measured by microscopy. Dihydroartemisinin-piperaquine (DHP) was dosed on days 0–2. Primaquine (PQ) was dosed on day 2. Error bars indicate the upper and lower limits of the 95% CI. *Indicates a statistically significant difference between groups based on a one-tailed Fisher’s exact test.</p

Kaplan-Meier survival curves of gametocyte clearance by treatment regimen.

<p>Twelve subjects that were gametocytemic at day 2, just prior to primaquine (PQ) dosing as measured by microscopy, are included. 95% confidence bands are shown.</p