POST-TREATMENT RECURRENCE OF PLASMODIUM VIVAX FOLLOWING CHLOROQUINE AND PRIMAQUINE THERAPY: A PVMSP-1 AND DIAGNOSTIC COMPARISON STUDY

Abstract

Plasmodium vivax remains a major contributor to global malaria morbidity, particularly due to its ability to form dormant liver stages (hypnozoites) that cause relapses weeks or months after initial infection. These relapses complicate malaria control and elimination strategies, especially in endemic regions. This study aimed to evaluate the efficacy of a directly observed 14-day primaquine regimen in preventing P. vivax recurrence and to assess the utility of diagnostic and molecular tools in differentiating relapses from reinfections. A total of 120 patients with microscopically confirmed mono-infection of P. vivax were enrolled. All participants received standard chloroquine therapy followed by a supervised 14-day primaquine regimen. Patients were monitored over a 90-day follow-up period using light microscopy, rapid diagnostic tests (RDTs), and polymerase chain reaction (PCR) targeting the PvMSP-1 gene. Recurrent infections were genotyped to distinguish true relapses from new infections. Out of the 120 patients, 8 (6.7%) experienced recurrence during follow-up. PCR identified all 8 cases (100%), compared to 7 (87.5%) by RDT and 6 (75%) by microscopy. Genotyping analysis revealed that 6 of the 8 recurrences (75%) were genetically homologous to the primary infection, indicating relapse, while 2 cases (25%) were heterologous, consistent with reinfection. The overall efficacy of the primaquine regimen was 93.3%. Notably, recurrent infections were more frequent among male patients and those residing in rural areas. Additionally, relapses were often characterized by low-density parasitemia, which was frequently undetected by conventional diagnostic methods. The study demonstrates the high effectiveness of a supervised 14-day primaquine course in reducing P. vivax relapses in G6PD-normal individuals. Furthermore, the incorporation of PCR-based diagnostics and PvMSP-1 genotyping enhances the ability to accurately differentiate relapse from reinfection. These molecular tools are valuable for improving surveillance, optimizing treatment strategies, and guiding malaria elimination efforts in endemic regions.