Severe and uncomplicated Plasmodium knowlesi malaria in North Kalimantan and Sabang, Aceh, and suspected Anopheles vectors across Kalimantan, Indonesia

BackgroundPlasmodium knowlesi is an emerging cause of zoonotic malaria in Southeast Asia. Current detection tools limit insight into the extent of transmission across Indonesia. This study aimed to enhance molecular and entomological surveillance around clinical cases to evaluate P. knowlesi transmission in Kalimantan and Aceh, Indonesia. MethodsFebrile patients presenting to district-level health facilities in Malinau, North Kalimantan, and Sabang, Aceh, were screened for malaria using routine diagnostic tools and ultrasensitive reverse-transcriptase PCR. Clinical and epidemiological data were collected. Overnight human landing catch mosquito surveys were conducted around P. knowlesi case locations in North Kalimantan. Anophelines were morphologically identified and compared to 2016-18 Ministry of Health entomology data across four Kalimantan provinces. Generalised linear mixed models (GLMM) compared mosquito group distributions across habitats. ResultsFrom December 2019 to September 2020, 429 patients were enrolled. Plasmodium knowlesi was the major cause of malaria transmission in Malinau and Sabang. In Malinau, 15/81 (18.5%) patients had malaria, comprising 10 (12.2%) P. knowlesi and 5 (6.1%) P. vivax infections. In Sabang, 6/348 (1.7%) patients had malaria, including 4 (1.1%) P. knowlesi infections. Two patients from Malinau met WHO-criteria for severe disease (hyperparasitaemia >100,000/{micro}L). Microscopy and pan-pLDH-based rapid diagnostic tests had >90% sensitivity for detecting P. knowlesi, although misidentification with P. vivax occurred. Risk-associations with P. knowlesi infection included forest-related activities, with all cases in adult males. Anopheles leucosphyrus group vectors (An. balabacensis and An. latens) were identified in farm, forest, and village environments in North Kalimantan, in coastal (An. hackeri), farm and forest (An. leucosphyrus) sites in Central Kalimantan, and forest sites (An. leucosphyrus) in South Kalimantan. GLMM analyses predicted fewer Anopheles leucosphyrus and barbirostris group mosquitoes in coastal habitats. Anopheles species diversity was highest in farm environments (mean Shannon-Weiner index H'=0.84, SD=0.49). ConclusionsPlasmodium knowlesi is a common cause of febrile illness and severe malaria in North Kalimantan. Findings support the need for ongoing access to appropriate diagnostics and treatment in non-zoonotic malaria elimination-phase settings. Competent vectors were found beyond traditional forest habitats across Kalimantan, with targeted vector monitoring and strengthened molecular surveillance essential for zoonotic malaria control efforts in Indonesia.