Actively Recruiting
Clinical Study to Assess Minimum Infective Mosquito Bites for Plasmodium Vivax Malaria Infection in Healthy Thai Adults Using Controlled Human Infection
Led by University of Oxford · Updated on 2026-03-27
24
Participants Needed
1
Research Sites
N/A
Total Duration
On this page
Sponsors
U
University of Oxford
Lead Sponsor
M
Mahidol University
Collaborating Sponsor
AI-Summary
What this Trial Is About
Researchers are studying the minimum number of mosquito bites infected with Plasmodium vivax needed to reliably cause malaria infection in healthy adults from Thailand. This study aims to develop a mosquito-delivered controlled human malaria infection (CHMI) model that better reflects natural transmission, supports safer vaccine testing, and improves relevance to endemic populations. The study is funded by the UK Wellcome Trust and builds on previous human challenge studies with P. vivax and P. falciparum. Participants will be exposed to bites from 1 to 3 P. vivax-infected mosquitoes in a sequential adaptive design to find the lowest infective dose. The study begins with one mosquito bite and increases to two or three if infection is not consistently achieved. This approach avoids excessive parasite exposure that could affect vaccine efficacy assessments. The research takes place at the Faculty of Tropical Medicine in Thailand, an expert center for malaria research. Volunteers will be closely monitored in a hospital setting until antimalarial treatment is completed and symptoms improve. Follow-up includes clinical assessments, immune response testing up to one year after treatment, and monitoring for any adverse events. The primary outcome is the minimum number of infected mosquito bites needed to cause infection within 21 days. Participants must remain reachable and reside locally during the study and follow-up period, which lasts about one year after treatment initiation.
CONDITIONS
Brief Title
Clinical Study to Assess Minimum Mosquito Bites for P. Vivax Infection in Thai Adults
Who Can Participate
Eligibility Criteria
You may qualify if you...
- Healthy adult aged 20 to 55 years weighing more than 50 kg
- No recent malaria infection
- Positive for Duffy antigen/chemokine receptor (DARC) on red blood cells
- CYP2D6 alleles consistent with normal metaboliser status
- Normal Glucose-6-phosphate dehydrogenase (G6PD) enzyme activity
- Women must use continuous effective contraception during the study and for 3 months after challenge
- Agreement to avoid blood donation during the study and for 1 year afterwards
- Willing to take curative antimalarial treatment after challenge
- Willing to be admitted for hospital monitoring until treatment completion and symptom resolution
- Willing to reside in Bangkok during clinical study and treatment
- Willing to be followed for 1 year after treatment starts
- Reachable by mobile phone 24/7 from challenge until treatment completion
- Able to read and write Thai and provide correct informed consent responses
- Provided written informed consent
- Low cardiovascular risk (less than 10% in 10 years)
- At least a bachelor's degree education
You will not qualify if you...
- History of clinical malaria
- Positive malaria PCR, film, or serology indicating recent exposure
- History of severe allergy to mosquito bites
- G6PD mutation
- Any medical condition posing undue risk or interfering with study results (e.g., serious cardiac, renal, hepatic, neurological disease; severe malnutrition; congenital defects; febrile illness)
- Chronic disease or regular medication use
- Planned travel outside Bangkok from challenge until 3 months after
- Use of systemic antibiotics with antimalarial activity within 30 days before challenge
- Use of immunoglobulins or blood products in the year before enrollment
- Receipt or planned receipt of investigational products or vaccines within 30 days before or during study
- Prior investigational vaccine likely to affect trial data
- Immunosuppressive or immunodeficient conditions including HIV, asplenia, or recurrent severe infections
- Immunosuppressant medications within 6 months before enrollment (except inhaled or topical steroids)
- Allergic diseases worsened by malaria infection
- Female participants who are pregnant, lactating, or planning pregnancy within 1 year post-challenge
- Contraindications to antimalarial drugs used in the study
- Use of medications known to interact with study antimalarials
- Use of drugs that may prolong QT interval
- Family history of early cardiac disease or sudden death
- Clinical conditions known to prolong QT interval
- History of cardiac arrhythmias including clinically significant bradycardia
- QTc interval ≥ 450 ms on screening ECG
- History of alcohol or drug abuse
- Concurrent participation in another clinical study during this study
- Abnormal liver, kidney, calcium, magnesium tests or low hemoglobin
- Thalassemia or hemoglobinopathies
- Positive for hepatitis B, hepatitis C, HIV, syphilis, or HTLV I/II infection
AI-Screening
AI-Powered Screening
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Your Study Journey
Duration - 2 to 4 weeks
Participants are screened for eligibility to participate in the trial.
1 visit (in-person)
Duration - Up to 21 days after mosquito bite challenge
Participants receive controlled bites from 1 to 3 Plasmodium vivax-infected mosquitoes to induce malaria infection, starting with one mosquito bite and escalating based on infection results.
Visits as needed for monitoring up to 21 days after challenge
Duration - Up to one year after antimalarial treatment initiation
Participants are monitored for immune responses and safety for up to one year after starting antimalarial treatment.
Multiple visits over one year for immune response and safety assessments
Trial Site Locations
Total: 1 location
1
Faculty of Tropical Medicine, Mahidol University
Bangkok, Thailand, 10400
Actively Recruiting
Research Team
N
Nicholas Day, MD
J
Jetsumon Sattabongkot Prachumsri, Ph.D
How is the study designed?
Study Type
INTERVENTIONAL
Masking
NONE
Allocation
NA
Model
SEQUENTIAL
Primary Purpose
OTHER
Number of Arms
1
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