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. 2014 Oct 2:13:390.
doi: 10.1186/1475-2875-13-390.

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

Timothy William, Jenarun Jelip, Jayaram Menon, Fread Anderios, Rashidah Mohammad, Tajul A Awang Mohammad, Matthew J Grigg, Tsin W Yeo, Nicholas M Anstey, Bridget E Barber  1
Affiliations

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

Timothy William et al. Malar J. .

Abstract

Background: While 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.

Methods: To 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.

Results: Notifications 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.

Conclusions: Notifications 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.

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Figures

Figure 1
Figure 1
Malaria notifications by species, 2004–2013. a. Inset graph shows malaria notifications 2011–2013 adjusted according to the estimated over/under diagnosis of each species calculated from the available microscopy and corresponding PCR results obtained from the State Reference Laboratory (data/calculations shown in Additional file 1). b. Percentage of total malaria notifications, 2004–2013.
Figure 2
Figure 2
Map showing districts and division of Sabah, with bar graphs showing annual Plasmodium malariae / Plasmodium knowlesi notifications, by division, from 2001–2013.
Figure 3
Figure 3
Malaria notifications by species and district, 2004–2013.
Figure 4
Figure 4
Plasmodium incidence by district, per 1,000 persons.
Figure 5
Figure 5
Age and sex distribution of Plasmodium malariae/Plasmodium knowlesi , Plasmodium falciparum and Plasmodium vivax mono-infections, from 2007–2013.
Figure 6
Figure 6
Monthly rainfall and notifications of Plasmodium malariae/Plasmodium knowlesi , for the districts of Kudat, Keningau, Tawau, Sandakan, and Kota Kinabalu. For illustrative purposes this figure excludes all data for Ranau as data are only available from July 2012, and all data from Jan-Jul 2009 as rainfall data from Keningau is not available from this time. Calculation of Spearman’s correlation coefficients includes all available data. Spearman’s correlation coefficients for association between monthly rainfall and notifications of P. malariae/P. knowlesi: 0.37 (p = 0.004), 0.32 (p = 0.016) and 0.30 (p = 0.024) for months 2, 3 and 4, respectively, following the rainfall.
Figure 7
Figure 7
Monthly notifications of Plasmodium malariae/Plasmodium knowlesi in Sabah.
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