Plasmodium knowlesi malaria in humans is widely distributed and potentially life-threatening

By J. Cox-Singh, T. Davis, Kim-Sung Lee, Sunita S. G. Shamsul, A. Matusop, Shanmuga Ratnam, H. A. Rahman, D. Conway, Balbir Singh. Clinical Infectious Diseases, 2008

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Background Until recently, Plasmodium knowlesi malaria in humans was misdiagnosed as P. malariae. The present objectives were to determine the geographic distribution of P. knowlesi in the human population in Malaysia and to investigate four suspected fatal cases. Methods Sensitive and specific nested-PCR was used to identify all Plasmodium species present in blood from i) 960 patients with malaria hospitalized in Sarawak, Malaysian Borneo from 2001-2006, ii) 54 P. malariae archival blood-films from 15 districts in Sabah, Malaysian Borneo (2003–2005) and four districts in Pahang, Peninsular Malaysia (2004–2005), and iii) suspected knowlesi fatalities. In the four latter cases, available clinical and laboratory data were reviewed. Results P. knowlesi DNA was detected in 266 of 960 (27·7%) of the samples from Sarawak hospitals, 41 of 49 (83·7%) from Sabah and all 5 from Pahang. Only P. knowlesi DNA was detected in archival blood films from the 4 fatal cases. All were hyperparasitemic and developed marked hepatorenal dysfunction. Conclusions Human infections with P. knowlesi, commonly misidentified as the more benign P. malariae, are widely distributed across Malaysian Borneo and extend to Peninsular Malaysia. Because P. knowlesi replicates every 24 hours, rapid diagnosis and prompt effective treatment are essential. In the absence of a specific routine diagnostic test for knowlesi malaria, we recommend that patients in, or who have travelled to, South-east Asia who are ill with a ‘P. malariae’ hyperparasitemia diagnosis by microscopy should receive intensive management as appropriate for severe falciparum malaria.

Subfields: Parasitology, Public Health, Environmental and Occupational Health, Surgery

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