Is a radical cure enough? Assessing a primaquine treatment for adult males in Cambodia to eliminate vivax malaria by 2025

Abstract Background: Elimination targets for Plasmodium vivax are approaching, wit the Cambodian target of 2025. Quantitative tools can assess if proposed strategies are likely to be sufficient to meet those targets. Methods: We calibrated the Optima Malaria transmission model to reported case data from 2011–2018 for six provinces with different transmission levels. The model had two human populations: males aged 15 years and older, and everyone else. We assessed the addition of the new low-dose primaquine intervention (0.25 mg/kg daily x 14 days) for diagnosed P. vivax infections where males aged 15 years and older were prescribed primaquine after testing glucose-6-phosphate-dehydrognase normal to the 2018 status quo (blood-stage treatment only). Results were evaluated over stochastic iterations of the calibrated compartmental model, incorporating best and worst case interpretations of the available case data given uncertainty over underlying P. vivax incidence in 2020.Results: Under 2018 status quo conditions in the absence of primaquine radical cure, we found that P. vivax elimination would be unlikely to be achieved by 2040 in any province. Elimination by 2025 was not projected in any province even with best case assumptions for primaquine intervention coverage, G6PD-based eligibility, and primaquine efficacy; however, we estimated that the addition of the primaquine intervention could reduce P. vivax transmission by 67%-83% by 2025. We found that sustained application of the primaquine intervention was likely to result in elimination by 2040 in all six provinces with best case estimated baseline incidence, and in the two lowest incidence provinces with worst case baseline incidence.Conclusions: Without additional novel interventions, the primaquine radical cure (0.25 mg/kg daily x 14 days targeting adult males with diagnosed P. vivax infections) is not projected to result in elimination from any province by the 2025 target even under the most optimistic interpretation of the available case data. However, the implementation of a primaquine intervention in Cambodia is likely to have a substantial impact on transmission of P. vivax and may make elimination feasible over the longer term.