Abstract
BackgroundThe simian parasite Plasmodium knowlesi is a common cause of human malaria in Malaysian Borneo, with a particularly high incidence in Kudat, Sabah. Little is known however about the epidemiology in this substantially deforested region.MethodsMalaria microscopy records at Kudat District Hospital were retrospectively reviewed from January 2009-November 2011. Demographics, and PCR results if available, were recorded for each positive result. Medical records were reviewed for patients suspected of representing family clusters, and families contacted for further information. Rainfall data were obtained from the Malaysian Meteorological Department.Results“Plasmodium malariae” mixed or mono-infection was diagnosed by microscopy in 517/653 (79%) patients. Of these, PCR was performed in 445 (86%) and was positive for P. knowlesi mono-infection in 339 (76%). Patients with knowlesi malaria demonstrated a wide age distribution (median 33, IQR 20–50, range 0.7-89 years) with P. knowlesi predominating in all age groups except those <5 years old, where numbers approximated those of Plasmodium falciparum and Plasmodium vivax. Two contemporaneous family clusters were identified: a father with two children (aged 10–11 years); and three brothers (aged one-11 years), all with PCR-confirmed knowlesi malaria. Cases of P. knowlesi demonstrated significant seasonal variation, and correlated with rainfall in the preceding three to five months.ConclusionsPlasmodium knowlesi is the most common cause of malaria admissions to Kudat District Hospital. The wide age distribution and presence of family clusters suggest that transmission may be occurring close to or inside people’s homes, in contrast to previous reports from densely forested areas of Sarawak. These findings have significant implications for malaria control. Prospective studies of risk factors, vectors and transmission dynamics of P. knowlesi in Sabah, including potential for human-to-human transmission, are needed.
Highlights
The simian parasite Plasmodium knowlesi is a common cause of human malaria in Malaysian Borneo, with a high incidence in Kudat, Sabah
The wide age distribution and presence of family clusters suggest that transmission may be occurring close to or inside people’s homes, in contrast to previous reports from densely forested areas of Sarawak
The highest proportion has been reported at Kudat District Hospital (KDH), on the north-east tip of Sabah, where 87% of patients admitted with malaria in 2009 were infected with P. knowlesi [8]
Summary
The simian parasite Plasmodium knowlesi is a common cause of human malaria in Malaysian Borneo, with a high incidence in Kudat, Sabah. Recent studies conducted in the densely forested Kapit District in Sarawak found that P. knowlesi primarily infected adults with a recent history of forest exposure, and that clustering of cases did not occur [4,10]. These findings suggest that in this region transmission occurs in forested areas away from people’s homes, and that human-to-human transmission, demonstrated experimentally [11], does not appear to be occurring. The epidemiology of malaria in Kudat from 2009–2011 was investigated
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