Characterizing Plasmodium vivax malaria in Ethiopia using PCR and serological assays in a P. falciparum co-endemic context: PvSTATEM baseline study

Abstract Background Eliminating Plasmodium vivax remains a formidable challenge due to dormant liver-stage parasites, hypnozoites, that cause relapses, evade detection, and sustain transmission. In the absence of diagnostic tools for hypnozoites, serological assays that capture recent exposure offer a promising indirect strategy to inform control and elimination programs. Methods To establish a baseline understanding of P. vivax epidemiology in a Plasmodium falciparum co-endemic setting in Ethiopia, we conducted an observational study in 36 clusters across West Arsi Zone, Oromia, between April and August 2024. Demographic, clinical, and behavioral data were collected, alongside capillary blood samples used for molecular detection of P. vivax and P. falciparum , and multiplex serological assays targeting eight P. vivax antigens. Mixed-effects logistic regression models were used to identify risk factors for infection and seropositivity, accounting for household and cluster-level clustering. Results Of the 7,920 targeted participants, 7,553 (95.36%) were enrolled, with balanced male-to-female ratio and a median age of 14 years (IQR: 7–29 years). The prevalence of P. vivax mono and mixed infection with P. falciparum by PCR was 6.1% (462/7,551) and 8.1% (609/7,551), respectively, while the corresponding prevalences for P. falciparum were 7.9% (57/7,551) and 9.9% (744/7,551). Seropositivity for P. vivax reached 41.33% (1,798/4,350), strongly correlating with cluster-level P. vivax PCR prevalence ( r  = 0.89; p <  0.001). Age-stratified analyses revealed cumulative exposure reflected in seropositivity, while PCR-detectable P. vivax infections peaked among school age children (9.6%, 263/2,730). Males, febrile individuals, and those reporting malaria within the past six months had significantly higher odds of P. vivax infection. G6PD enzyme deficiency was rare, observed in 0.25% of males and 0.76% of females. Conclusion This baseline study highlights substantial and heterogenous P. vivax transmission in West Arsi, underestimated by molecular diagnostics alone. The large reservoir of recent exposure revealed through serology, combined with the very rare G6PD deficiency, supports serology as a promising tool to identify populations at risk of relapse and strengthens the feasibility of targeted radical cure strategies for elimination efforts.