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Plasmodium knowlesi infection: a diagnostic challenge
  1. Lijia Fan1,
  2. Shir Ying Lee2,
  3. Evelyn Koay3,
  4. Christian Harkensee1
  1. 1Department of Paediatrics, National University Health System, Singapore, Singapore
  2. 2Department of Haematology Oncology, National University Health System, Singapore, Singapore
  3. 3Department of Laboratory Medicine, National University Health System, Singapore, Singapore
  1. Correspondence to Dr Lijia Fan, Li_jia_fan{at}


Plasmodium knowlesi malaria is an uncommon, but highly prevalent parasitic infection in parts of Malaysia. This is the case of a 14-year-old Singaporean boy presenting to our emergency department with an 11-day history of fever following a school trip to Malaysia. Hepatosplenomegaly was the only clinical finding; laboratory tests showed thrombocytopaenia, lymphopaenia, mild anaemia and liver transaminitis. Specific malaria antigen tests were negative, but the peripheral blood film showed plasmodia with atypical features, with a parasite load of 0.5%. PCR confirmed the diagnosis of P knowlesi. The patient was successfully treated with chloroquine. The clinical course of P knowlesi malaria is indistinguishable from that of Plasmodium falciparum. This case highlights the importance of taking detailed travel history, careful examination of malaria blood films and judicious use of molecular techniques. Antigen tests alone may have missed a malaria diagnosis altogether, while blood film examination may wrongly identify the species as Plasmodium malariae or P falciparum. Third-generation PCR assays can be used to reliably identify P knowlesi.

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