Introduction: Malaysia aims to eliminate human-only malaria by 2020. While cases of P. falciparum and P. vivax have fallen substantially, the incidence of zoonotic malaria from P. knowlesi continues to increase, presenting a major challenge to regional malaria control efforts.
Methods: We are conducting prospective surveillance studies in Sabah, Malaysia, determining trends in state-wide malaria incidence, clinical spectrum and deaths. Health staff at hospitals and District Health Offices across Sabah collect demographic and clinical data for all malaria diagnoses. PCR for Plasmodium species is performed at the State Reference Laboratory. Data are cross-checked against Ministry of Health malaria-notification and State Reference Laboratory databases. Data from 2015-17 were reviewed including case-notes of malaria deaths.
Results: In 2017, 2102 malaria diagnoses were recorded, with P. knowlesi by microscopy accounting for 2030/2058 (98.6%) available microscopy results. PCR was performed on 1822/2102 (87%) malaria patients, with P. knowlesi accounting for 1762 (96.7%), more than double the number of P. knowlesi cases recorded in 2015 (n=850) and the highest reported incidence to-date. In contrast, in 2017 PCR-confirmed P. falciparum and P. vivax accounted for 22 (1.2%) and 8 (0.4%) cases respectively, compared to 108 and 63 in 2015. Six malaria deaths occurred 2015-2017, all from P. knowlesi. Among fatal cases, novel predisposing factors were present in half, including pregnancy, morbid obesity and severe valvular heart disease. Delays in first presentation were common, with median duration of fever of 8 days (range 4-14).
Conclusions: P. knowlesi represents a major obstacle to malaria elimination in co-endemic countries in the region. Wider molecular testing for P. knowlesi, and reporting as such, is required in co-endemic countries, and malaria control programs require interventions effective against P. knowlesi. Strategies to improve awareness, earlier presentation, correct diagnosis and early use of intravenous artesunate, when indicated, should reduce case-fatality.