This research is intended to study the efficacy of chloroquine (CQ) and primaquine (PQ) for Plasmodium vivax (P.vivax) infection, and also to study the recurrence rate among patients with P.vivax malaria on standard doses of CQ and PQ. For this study, PQ will be withheld for 28 days so as to study the efficacy of CQ alone.

This study will assess whether CQ is still effective against P.vivax or whether there are resistant P.vivax strains in Bhutan.

This study aims to assess the efficacy of Chloroquine alone, withholding Primaquine until day 28. Parasitic clearance and recurrence rates will be recorded. Patients whose blood stage of parasites are not cleared with the standard dose of Chloroquine, or any recurrences before day 28, will be treated with second line treatment (ACT).

The patients blood level of Chloroquine (drug concentration) at the time of a recrudescent infection will de determined to assess whether that could be due to resistance, or due to low level of Chloroquine.

Any relapses occurring after day 28 when not receiving Primaquine, or after completion of Primaquine dosage for a total of 14 days (from day 29 to 42), will be treated with repeat doses of the initial treatment. The recurrence rates will be recorded so as to develop the next phase of the study where the two different doses of Primaquine (high dose vs. low dose) will be compared.

Inclusion Criteria:

• >12 months of age
• infection with P.vivax parasitaemia monoinfection
• presence of axillary temperature >37.5 degrees or history of fever during the past 24 hours
• ability to swallow oral medication
• ability and willingness to comply with the study protocol for the duration of the study, including 12 months follow up
• informed consent from the patient/parent/guardian in the case of children

Exclusion Criteria:

• Presence of general danger signs in children aged under 5 years or signs of severe malaria according to the definitions of WHO
• Presence of severe malnutrition (defined as a child whose growth standard is below -3 z-score, has symmetrical oedema involving at least the feet or has a mid-upper arm circumference < 110 mm);
• History of haemolysis or severe anaemia
• Acute anaemia <7 mg/dL
• Presence of febrile conditions due to diseases other than malaria (e.g. measles, acute lower respiratory tract infection, severe diarrhoea with dehydration) or other known underlying chronic or severe diseases (e.g. cardiac, renal and hepatic diseases, HIV/AIDS);
• Regular medication, which may interfere with antimalarial pharmacokinetics
• History of hypersensitivity reactions or contraindications to any of the medicine(s) being tested or used as alternative treatment(s)
• a positive pregnancy test or lactating

Patients with P.vivax infections will be recruited from 6 sentinel sites and will be recruited for the study after informed consent is received.

An amendment has been approved to extend the study to 12 sites.