Submicroscopic burden of zoonotic P. knowlesi malaria on Mursala Island and P. falciparum and P. vivax transmission in mainland North Sumatra, Indonesia

Accurate molecular tools are essential for estimating zoonotic malaria transmission in Southeast Asia. This study applied ultrasensitive reverse-transcriptase real-time PCR to detect zoonotic malaria in febrile patients from eight mainland health facilities and Mursala Island, spanning three districts in North Sumatra, Indonesia. Among 64 participants on Mursala, 7 (10.9%) had confirmed Plasmodium knowlesi symptomatic infections, including two submicroscopic infections associated with severe anaemia. All were negative by microscopy and pan-pLDH rapid diagnostic tests. No P. knowlesi infections were identified among 947 participants from mainland sites; PCR detected malaria in 34%, including P. vivax (17.5%) and P. falciparum (7.5%). Of these, 30% were submicroscopic infections. No P. cynomolgi infections were identified. P. knowlesi transmission is low in North Sumatra, however, may cause serious disease. Molecular diagnostics remain crucial for identifying zoonotic malaria and should be integrated into surveillance systems to inform public health control measures.