This study aims to determine whether a 14 day course of 0.5 mg/kg/day primaquine can eliminate subclinical P. vivax infections detected by high volume ultra-sensitive PCR (uPCR).

This is a randomized, Single blind trial in G6PD normal participants with subclinical P. vivax infections in Laos. Participants with subclinical P. vivax infections and those meeting the enrolment criteria will be randomly assigned to one of two treatment arms:

• Intervention: Dihydroartemisinin-piperaquine (DP) therapy 3 days dosing plus 14 days of supervised primaquine (7mg/kg total dose) administered once per day (0.5 mg/kg/day).
• Control arm: Dihydroartemisinin-piperaquine (DP) 3 days dosing therapy plus 14 days identical primaquine placebo.

Participants found to be G6PD deficient (G6PDd) will be treated with primaquine 0.75mg/kg/week for 8 weeks according to WHO recommendations. Primaquine and placebo will be administered with food (biscuits), which has been shown to reduce gastrointestinal side effects. All doses of study drugs will be supervised. If participants cannot visit the study centre, or fail to attend during the 14 days of supervised therapy, team members will visit them in their homes, schools or work to ensure complete dosing.

Findings:

The study showed that a 14-day course of primaquine added to mass drug administration with dihydroartemisinin-piperaquine prevented recurrent asymptomatic P. vivax infections (doi: 10.1186/s12936-019-3091-5)

Inclusion Criteria:

• Participants with subclinical mono- or mixed P. vivax infections (uPCR) can be enrolled.
• Able to participate as decided by the investigators, and willing to comply with the study requirements and follow-up.
• A participant (or parent/guardian of children below age of consent) is willing and able to give written informed consent to participate in the trial.

Exclusion Criteria:

• Currently pregnant or breastfeeding (female of child-bearing age).
• Inability to tolerate oral treatment.
• Previous episode of haemolysis or severe haemoglobinuria following primaquine.
• Known hypersensitivity or allergy to the study drugs.
• Blood transfusion in last 90 days, since this can mask G6PD deficiency.
• An acute malaria episode requiring treatment.
• A febrile condition due to diseases other than malaria (e.g. measles, acute lower respiratory tract infection, severe diarrhoea with dehydration).
• Anaemia (Haemoglobin (Hb) < 9 g/dL
• Presence of any condition which in the judgment of the investigator would place the participant at undue risk or interfere with the results of the study (e.g. serious underlying cardiac, renal or hepatic disease; severe malnutrition; HIV/AIDS; or severe febrile condition other than malaria); co-administration of other medication known to cause haemolysis or that could interfere with the assessment of antimalarial regimens.
• Currently taking medication known to interfere significantly with the pharmacokinetics of primaquine and the schizontocidal study drugs