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

Abstract

Background: Single low dose primaquine (SLD PQ, 0.25mg/kg) is recommended in combination with artemisinin-based combination therapy (ACT) as a gametocytocide to prevent Plasmodium falciparum 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.

Methods: 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 Anopheles dirus on days 0, 3, 7, and 14 of blood-stage therapy. Gametocytemia was evaluated by microscopy and reverse-transcriptase PCR.

Results: 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.

Conclusions: 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.

Fig 1. Schematic of gametocyte and mosquito infectivity status through treatment in 101 randomized participants.

Participants in the primaquine (PQ) and non-primaquine arms are depicted in the same ordered configuration from Day 0 pre-treatment through Week 2 post-treatment. Subjects with patent gametocytes detected by microscopy are colored black, while subjects who infected at least one mosquito on membrane feeding are colored blue. Persons that were both gametocytemic and infectious are colored half black-half blue. Persons who missed follow-up are shown as missing.

Fig 2. Gametocyte prevalence during 42-day follow-up.

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.

Fig 3. Kaplan-Meier survival curves of gametocyte clearance by treatment regimen.

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.

Fig 4. Relationship of microscopic gametocytemia to prevalence of mosquito infection.

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 Table 3. Note pre-treatment data (black circles) were previously presented in Ref 18.