Low prevalence of sub-microscopic malaria among rural communities of an endemic area in Kapit Division, Malaysian Borneo

Abstract

Background Malaria remains a major public health concern, especially with zoonotic Plasmodium knowlesi presenting specific challenges in Southeast Asia. In Malaysia, Sarawak ranks second in P. knowlesi cases after Sabah. Rural populations in endemic areas experience increased exposure to forest and forest-edge zones where vector mosquitoes breed, thereby raising infection risk and complicating routine surveillance. These groups may carry asymptomatic or submicroscopic infections that act as hidden reservoirs, potentially hindering elimination efforts. This study aimed to assess the prevalence of Plasmodium infections, including submicroscopic cases, among rural communities in Kapit Division, a malaria-endemic area.

Methods A cross-sectional study was conducted from March 2024 to August 2025, including 376 participants aged 2 to 90 years. Venous blood samples were examined under a light microscope with Giemsa-stained thick and thin smears. Additionally, all samples underwent species-specific nested PCR to verify microscopy results and identify sub-microscopic infections. Hemoglobin levels were measured using a HemoCue® Hb 201 + analyzer. Face-to-face interviews were conducted using a standardized questionnaire. The data analysis was performed with IBM SPSS version 27.0.

Results The overall malaria prevalence was 5.32% (20/376; 95% CI 3.47–8.07%). Of these, 18 (90%; 18/20) infected individuals were febrile and microscopy-positive. Nested PCR detected two additional afebrile, submicroscopic infections (10%; 2/20). Molecular speciation identified 16 P. knowlesi, one P. falciparum, and one P. vivax among febrile participants. Both submicroscopic cases were P. knowlesi. All infections occurred in the Kapit District. Anemia was found in 17.6% (66/376) of participants. Of these, 4 were positive for P. knowlesi, with no significant association with the infection. Infection was significantly associated with age over 40 years (p = 0.02), non-field employment (p = 0.003), and higher household income (p < 0.001).

Conclusion This study shows low Plasmodium infection rates in Kapit, with some submicroscopic infections. This emphasizes the importance of molecular surveillance in eliminating malaria, as traditional diagnostics may overlook hidden reservoirs. To monitor ongoing transmission, prevent re-establishment of local human malaria, and control zoonotic P. knowlesi, routine surveillance should include both PCR and microscopy in endemic areas.