Description
Introduction – Objectives
Eliminating Plasmodium vivax poses challenges, primarily due to the high rate of infection resulting of hypnozoites reactivation if untreated. Testing and Treatment (TAT) strategies could pave the way for P. vivax elimination in low-transmission settings, but the absence of sensitive field tests to diagnose either the blood stages or the hypnozoite carriers remains a gap. Recent advancements in Polymerase Chain Reaction (PCR) and serology position them as promising tools to address these challenges. This study aims to describe a PCR-based TAT strategy (PCRTAT) implemented in Saint Georges de l’Oyapock (SGO), French Guiana, along with alternative strategies (seroTAT and seroPCRTAT) that could have been employed.
Methodology
PALUSTOP cohort survey was implemented in SGO from September 2017 to December 2018. Participants were screened at their inclusion for P. vivax carriage using PCR tests, and treated if positive. Participants were also tested by serology. Passive detection of P. vivax infection was implemented at the health center during the study period. Participants were categorized into theoretical overlapping treatment groups based on their 2017 PCR and serological results: those treated in PALUSTOP PCRTAT (positive PCR regardless of serology), and those treated in theoretical seroTAT (seropositive) and theoretical seroPCRTAT (PCR positive and/or seropositive).
Strategies were described in terms of participants targeted or missed, primaquine contraindications (pregnancy, G6PD severe or intermediate deficiency) and sociodemographic characteristics.
Furthermore, we compared the rates of P. vivax infection in the year following the test – diagnosed either at the health center or reported by participants – among the PALUSTOP-treated individuals, those who would have been additionally treated under seroPCRTAT, and those who would not have received treatment.
Results and Discussions
In 2017, of the 1567 included inhabitants, aged 0 to 92 years, 90 (6%) were P. vivax carriers with 74% of them seropositive (n=67), while an additional 323 participants were seropositive without P. vivax carriage for a total of 390 seropositive (25%). Across all evaluated strategies, 13% to 17% of participants had primaquine contraindications. PCRTAT missed 285 seropositive individuals while seroTAT would have missed 21 PCR-positive cases. The group that would have been additionally treated if seroPCRTAT had a higher risk of P. vivax infection in the following year than the untreated if seroPCRTAT (9% vs 2%). Those results highlight the challenges of selecting the most effective option into the real-world implementation of these strategies as both PCRTAT and seroTAT missed or would have missed potential P. vivax or hypnozoites carriers.
Conclusions
Serology and PCR are promising tools for implementing targeted treatment strategies in low-transmission settings of P. vivax, when field compatible sensitive tests will be available. Both seem necessary to capture blood stages and potential hypnozoite carriers, while avoiding the use of mass treatment. However, the high rate of primaquine contraindications and challenges with adherence to this long-posology scheme drugs need consideration when implementing these strategies to achieve elimination.
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