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

NCT07257965 | Recruiting DMC

• 1 other identifier: MAL25001
• Study Type: interventional
• Target: 24
• Locations: 1 country
• Sites: 1

Brief Summary

This study is a human challenge study to assess the minimum infective mosquito bite dose in a controlled human malaria Infection (via P. vivax sporozites) in healthy volunteers. The results will inform the development of a P. vivax mosquito-delivered CHMI trial platform, supporting safer and more accurate vaccine efficacy assessments. Conducting the trial in individuals genetically and immunologically similar to the target population will also enhance the relevance of findings to real-world endemic settings. This study is funded by the UK Wellcome Trust. The grant reference number are Oxford/MORU: 212336/Z/18/Z and 212336/Z/18/A, and Mahidol University: 212336/A/18/Z and 212336/A/18/A.

Conditions

Plasmodium Vivax Infection

Keywords

Malaria; Mosquito bite; Plasmodium Vivax Infection

Outcome Measures

Primary Outcomes (1)

• The minimum number of infected mosquito bites.

  The minimum number of infected mosquito bites needed to reliably result in a P.vivax infection in all 8 participants at a given bite dose group, as defined by two consecutive positive qPCR results or presence of parasitemia on malaria blood film

  Up to 21 days after the individual CHMI

Secondary Outcomes (7)

• Prepatent period across different groups.

  Up to 21 days after the individual CHMI

• Humoral immune responses

  Up to one year after antimalarial initiation

• Humoral immune responses

  Up to one year after antimalarial initiation

• Cellular immune responses

  Up to one year after antimalarial initiation

• Cellular immune responses

  Up to one year after antimalarial initiation

Study Arms (1)

Number of mosquito bite (1 or 2 or 3)

EXPERIMENTAL

Number of mosquito bites assigned sequentially based on the adaptive design

Other: Mosquito bite (1 or 2 or 3)

Interventions

Mosquito bite (1 or 2 or 3) OTHER

Successful feeding of 1, 2, or 3 Plasmodium vivax-infected mosquitoes

Number of mosquito bite (1 or 2 or 3)

Eligibility Criteria

• Age: 20 Years - 55 Years
• Sex: all
• Healthy Volunteers: Yes
• Age Groups: Adult (18-64)

You may qualify if:

• Healthy adult aged 20 to 55 years with weight more than 50 kg.
• No recent malaria infection.
• Red blood cells positive for the Duffy antigen/chemokine receptor (DARC).
• CYP2D6 alleles consistent with normal metaboliser status.
• Normal level of Glucose-6-phosphate dehydrogenase (G6PD) enzyme activity by the WHO definition.
• Women only: Must practice continuous effective contraception for the duration of study period until 3 months post-challenge.
• 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.
• Willing to take a curative antimalarial regimen following challenge.
• Willing to be admitted in the Hospital for Tropical Diseases for clinical monitoring until antimalarial treatment (chloroquine) is completed and their symptoms are settling.
• Willing to reside in Bangkok for the duration of the clinical part of the study, until all antimalarial treatment has been completed.
• Willing to be followed up for 1 year post treatment initiation.
• Reachable (24/7) by mobile phone during the period between challenge CHMI and completion of all antimalarial treatment.
• Able to read and write in Thai and able to answer ALL questions on the informed consent questionnaire correctly.
• Provided written informed consent to participate in the trial.
• 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)

Sponsors & Collaborators

• University of Oxford: lead
• Mahidol University: collaborator

Study Sites (1)

Faculty of Tropical Medicine, Mahidol University

Bangkok, 10400, Thailand

RECRUITING

MeSH Terms

Conditions

Malaria

Condition Hierarchy (Ancestors)

Protozoan Infections; Parasitic Diseases; Infections; Mosquito-Borne Diseases; Vector Borne Diseases

Study Officials

• Nicholas Day, MD

  University of Oxford

  PRINCIPAL INVESTIGATOR

• Jetsumon Sattabongkot Prachumsri, Ph.D

  Mahidol University

  PRINCIPAL INVESTIGATOR

Central Study Contacts

Nicholas Day, MD

CONTACT

+66-(0)2-3549170; nickd@tropmedres.ac

Jetsumon Sattabongkot Prachumsri, Ph.D

CONTACT

+66-(0)2-3549100; jetsumon.pra@mahidol.ac.th

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: NA
• Masking: NONE
• Purpose: OTHER
• Intervention Model: SEQUENTIAL
• Sponsor Type: OTHER
• Responsible Party: SPONSOR

Model Details: Three groups assigned sequencially. This is a single-centre, adaptive-design, Plasmodium vivax sporozoite-stage mosquito-bite Controlled Human Malaria Infection (CHMI) trial conducted in healthy, malaria-naïve Thai adults

Study Record Dates

• First Submitted: November 14, 2025
• First Posted: December 2, 2025
• Study Start: February 2, 2026
• Primary Completion (Estimated): August 31, 2027
• Study Completion (Estimated): August 31, 2027
• Last Updated: March 27, 2026

Record last verified: 2026-03

Data Sharing

• IPD Sharing: Will share
• Shared Documents: STUDY PROTOCOL, SAP
• Time Frame: After completion of trial activities and once the study data have already been used for the study purposes, including publication.

Locations

TH (1)