Changing epidemiology of malaria in Sabah, Malaysia: increasing incidence of Plasmodium knowlesi

Abstract

BackgroundWhile Malaysia has had great success in controlling Plasmodium falciparum and Plasmodium vivax, notifications of Plasmodium malariae and the microscopically near-identical Plasmodium knowlesi increased substantially over the past decade. However, whether this represents microscopic misdiagnosis or increased recognition of P. knowlesi has remained uncertain.MethodsTo describe the changing epidemiology of malaria in Sabah, in particular the increasing incidence of P. knowlesi, a retrospective descriptive study was undertaken involving a review of Department of Health malaria notification data from 2012–2013, extending a previous review of these data from 1992–2011. In addition, malaria PCR and microscopy data from the State Public Health Laboratory were reviewed to estimate the accuracy of the microscopy-based notification data.ResultsNotifications of P. malariae/P. knowlesi increased from 703 in 2011 to 815 in 2012 and 996 in 2013. Notifications of P. vivax and P. falciparum decreased from 605 and 628, respectively, in 2011, to 297 and 263 in 2013. In 2013, P. malariae/P. knowlesi accounted for 62% of all malaria notifications compared to 35% in 2011. Among 1,082 P. malariae/P. knowlesi blood slides referred for PCR testing during 2011–2013, there were 924 (85%) P. knowlesi mono-infections, 30 (2.8%) P. falciparum, 43 (4.0%) P. vivax, seven (0.6%) P. malariae, six (0.6%) mixed infections, 31 (2.9%) positive only for Plasmodium genus, and 41 (3.8%) Plasmodium-negative. Plasmodium knowlesi mono-infection accounted for 32/156 (21%) and 33/87 (38%) blood slides diagnosed by microscopy as P. falciparum and P. vivax, respectively. Twenty-six malaria deaths were reported during 2010–2013, including 12 with ‘P. malariae/P. knowlesi’ (all adults), 12 with P. falciparum (seven adults), and two adults with P. vivax.ConclusionsNotifications of P. malariae/P. knowlesi in Sabah are increasing, with this trend likely reflecting a true increase in incidence of P. knowlesi and presenting a major threat to malaria control and elimination in Malaysia. With the decline of P. falciparum and P. vivax, control programmes need to incorporate measures to protect against P. knowlesi, with further research required to determine effective interventions.Electronic supplementary materialThe online version of this article (doi:10.1186/1475-2875-13-390) contains supplementary material, which is available to authorized users.

A Sensitive, Colorimetric, High-Throughput Loop-Mediated Isothermal Amplification Assay for the Detection of Plasmodium knowlesi

“…1 In Sabah, Malaysia, while the total number of reported malaria cases has decreased since 1992, the absolute number and proportion due to P. knowlesi have increased significantly such that in 2013, 62% of malaria notifications were due to P. knowlesi, making it the most common cause of malaria in this region. 2 Plasmodium knowlesi malaria is difficult to diagnose by conventional microscopy. Ring and trophozoite stages of P. knowlesi appear morphologically very similar to both Plasmodium falciparum and Plasmodium malariae.…”

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“…According to retrospective review of Sabah Department of Health malaria notification data from 1992-2013, the percentage of malaria cases in Sabah caused by P. malariae/P. knowlesi was on the increasing trend from 1% in 1992 to 35% in 2011 and to 62% in 2013 [8] [9].…”