Plasmodium Vivax Malaria Clinical Trial
Official title:
Development of a Safe and Reproducible Human Sporozoite Challenge Model for Plasmodium Vivax in Healthy Adults in the United States
The purpose of this study is to demonstrate that volunteers can be safely and reproducibly infected with Plasmodium vivax (P. vivax) by the bites of experimentally infected Anopheles dirus (An. dirus) mosquitoes carrying P. vivax sporozoites in their salivary glands.
The study is a proof-of-concept clinical investigation designed to develop a safe and
practical sporozoite challenge model for Plasmodium vivax in humans with a goal of 100%
infectivity rate. The development and standardization of such a model will make possible
efficacy evaluations of candidate P. vivax vaccines in Phase 2a trials. This trial is
conducted in collaboration with Armed Forces Research Institute of Medical Sciences (AFRIMS)
investigators in Bangkok, Thailand, who will be recruiting adult blood donors from a pool of
patients who present with active P. vivax infections in Thailand. Samples of P. vivax
infected blood will be collected and fed via membrane feeding apparatus to colony-reared
Anopheles dirus mosquitoes at the AFRIMS Entomology Lab. A portion of the same blood will
meanwhile be screened for potential co-infections at the AFRIMS Retrovirology Laboratory.
When screening tests have confirmed the presence of only P. vivax in the blood (no
co-infections with other malaria species), and selected dissection on days 3-7 has revealed
oocyst production in the blood-fed mosquitoes, the mosquitoes will be transported from the
AFRIMS insectary in Thailand to the WRAIR insectary in the US by a standard procedure (herein
described) including permits and assurance against accidental release of the infected
mosquitoes. Transport will be conducted in compliance with Thai exporting and US importing
requirements.
Our study will involve two cohorts, each to be challenged once, in the hope of demonstrating
reproducibility of the entire challenge procedure. Each cohort comprises up to 6 healthy
adult volunteers. The first cohort will be challenged with 5 bites from P. vivax-infected
mosquitoes each carrying at least a grade 2 sporozoite infection (>10 sporozoites in salivary
gland).
If all six volunteers in the first cohort develop P. vivax infection, the same procedure will
be repeated in the second cohort. If the first cohort has less than 100% infectivity rate,
the second cohort will be challenged with up to 10 grade 2 infective bites to ensure 100%
infectivity rate. Volunteers will be closely monitored post-infection, and will be treated
with standard chloroquine and primaquine therapies when the infection becomes patent in the
peripheral blood.
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