3^rd Edition of Infectious Diseases World Conference 2026

Abstract

Simian malaria is a significant emerging health concern in Southeast Asia, with zoonotic malaria infections caused by parasites such as Plasmodium knowlesi, P. cynomolgi, and P. inui. Effective control and eradication of malaria require the development of rapid, specific, and sensitive diagnostic assays to detect infections in non-human primates, which serve as reservoirs for these zoonotic pathogens. Although the Rapid Diagnostic Test (RDT) has been widely implemented for detecting human malaria infections, their applicability for diagnosing simian malaria remains unclear. This study aimed to evaluate the sensitivity and specificity of the Malaria Ag Pf/Pan rapid test (BiolineTM, South Korea) for detecting simian malaria in blood samples collected from Thai cynomolgus macaques (Macaca fascicularis). Seventy-five blood samples were obtained from wild macaques in Ranong Province, southern Thailand, where human-macaque interaction occurred. Malaria parasites in these samples were detected using the Pf/Pan RDT, and the results were compared with microscopic examination (a classical method) and nested PCR analysis (a reference standard). The comparison of time consumption revealed that RDT is the fastest method, delivering results within 15 minutes. In contrast, nested PCR requires approximately 2 hours, and microscopic examination varies depending on the specialist. The diagnostic performance of the tests was assessed using Kappa (κ) and McNemar's tests. Statistical analysis revealed that when compared to nested PCR, microscopy demonstrated a sensitivity of 29.73%, a specificity of 100%, and fair agreement (κ = 0.3). The RDT showed a sensitivity of 27%, a specificity of 100%, and similar fair agreement (κ = 0.273). The nested PCR analysis revealed statistically significant differences when compared to both microscopy and RDT (p < 0.001). Both microscopy and RDT exhibited a positive predictive value (PPV) of 100%, ensuring accurate identification of positive cases, but their negative predictive values (NPVs) were low (59.38% and 58.46%, respectively), indicating a high rate of false negatives. When compared between RDT and microscopy, the RDT demonstrated lower sensitivity (81.82% for RDT and 96.92% for microscopy) and comparable specificity (98.44% for RDT and 90.00% for microscopy). Both comparisons showed almost perfect agreement (κ = 0.834) and no significant differences in diagnostic performance (p = 1). Confirming with nested PCR, the RDT could detect three simian malaria species: P. knowlesi, P. inui, and P. cynomolgi. In conclusion, RDT is a sensitive and specific method for diagnosing at least three species of simian malaria in Cynomolgus macaques, with performance comparable to classical microscopic technique. These findings suggest that RDT could be effectively applied for rapid screening of simian malaria infections in macaques, especially in the field setting where the wild-caught non-infected animals need to be released to their natal habitat as soon as they recover from anesthetization.