Clinical Study to Assess Minimum Mosquito Bites for P. Vivax Infection in Thai Adults

inclusion criteria 1. Healthy adult aged 20 to 55 years with weight more than 50 kg. 2. No recent malaria infection. 3. Red blood cells positive for the Duffy antigen/chemokine receptor (DARC). 4. CYP2D6 alleles consistent with normal metaboliser status. 5. Normal level of Glucose-6-phosphate dehydrogenase (G6PD) enzyme activity by the WHO definition. 6. Women only: Must practice continuous effective contraception for the duration of study period until 3 months post-challenge. 7. Agreement to refrain from blood donation during the course of the study and for 1 year after the end of their involvement in the study. 8. Willing to take a curative antimalarial regimen following challenge. 9. Willing to be admitted in the Hospital for Tropical Diseases for clinical monitoring until antimalarial treatment (chloroquine) is completed and their symptoms are settling. 10. Willing to reside in Bangkok for the duration of the clinical part of the study, until all antimalarial treatment has been completed. 11. Willing to be followed up for 1 year post treatment initiation. 12. Reachable (24/7) by mobile phone during the period between challenge CHMI and completion of all antimalarial treatment. 13. Able to read and write in Thai and able to answer ALL questions on the informed consent questionnaire correctly. 14. Provided written informed consent to participate in the trial. 15. Cardiovascular risk assessment is low (less than 10% in the next 10 years according to the cardiovascular risk assessment from Thai NCD Division, DDC, MoPH (2016) 16. Educational level: has at least a bachelor's degree. The volunteer MUST NOT enter the study if any of the following apply: 1. History of clinical malaria. 2. Positive malaria PCR OR malaria film OR malaria serology (recent exposure by Multiplex Bead Based Immunoassay) 3. History of severe allergy to mosquito bite 4. G6PD mutation 5. Presence of any medical condition (either physical or psychological) 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, hepatic or neurological disease; severe malnutrition; congenital defects or febrile condition) 6. Presence of chronic disease or chronically use of medication. 7. Plan to travel outside of Bangkok within the period of challenge until 3 months after. 8. Use of systemic antibiotics with known antimalarial activity in the 30 days before challenge (e.g. trimethoprim-sulfamethoxazole, doxycycline, tetracycline, clindamycin, erythromycin, fluoroquinolones and azithromycin). 9. Use of immunoglobulins or blood products (e.g. blood transfusion) at any time in the year preceding enrolment. 10. Receipt of an investigational product or any vaccine in the 30 days preceding enrolment (D0), or planned receipt during the study period. 11. Prior receipt of an investigational vaccine likely to impact on interpretation of the trial data or the P. vivax parasite as assessed by the Investigator. 12. Any confirmed or suspected immunosuppressive or immunodeficient state, including HIV infection, asplenia, history of splenectomy, recurrent, severe infections, and chronic infection. 13. Immunosuppressant medication within the past 6 months preceding enrolment (D0) (inhaled and topical steroids are allowed). 14. History of allergic disease or reactions likely to be exacerbated by malaria infection. 15. Female participant who is pregnant and, lactating during the course of the study, or planning pregnancy within 1 year post-challenge. 16. Contraindications to the use of antimalarial treatment (e.g. chloroquine or primaquine or atovaquone / proguanil, DHA piperaquine). 17. Use of medications known to have a potentially clinically significant interaction with antimalarial drug that will be used in this study (chloroquine or primaquine or atovaquone / proguanil, DHA/ piperaquine). 18. Use of medications known to cause prolongation of the QT interval as state in the section of prohibited drugs that may have effect on prolongation of the QT interval.\* 19. Known existing positive family history in both 1st AND 2nd degree relatives \< 50 years old for cardiac disease. 20. Family history of congenital QT prolongation or sudden death. 21. Any clinical condition known to prolong the QT interval. 22. History of cardiac arrhythmia, including clinically relevant bradycardia. 23. Screening ECG demonstrates a QTc interval ≥ 450 ms 24. Suspected or known or history of alcohol abuse 25. Suspected or known or history of drug abuse. 26. Concurrently participating in another clinical study, at any time during the study period. 27. Finding on safety laboratory values as defined below: * Abnormal ALT \[\>upper normal range\] * Abnormal serum creatinine \[\>upper normal range\] * Clinically significant abnormalities in corrected calcium and magnesium blood levels * Haemoglobin \< 11 g/dL * HbA1C \>upper normal range 28. Thalassaemia disease or haemoglobinopathies. 29. Positive hepatitis B surface antigen or seropositive for hepatitis C virus, or HIV, Syphilis, HTLVI/II