Knowlesi malaria — DTM&H MCQ
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Correct answer: C — Plasmodium knowlesi malaria
The correct answer is C, Plasmodium knowlesi malaria. P. knowlesi is a zoonotic simian parasite endemic to Malaysian Borneo and South East Asia, and its mature blood stages closely resemble P. malariae on thin film, causing frequent microscopic misdiagnosis. Unlike P. malariae, which has a 72 hour (quartan) erythrocytic cycle, P. knowlesi has a 24 hour cycle, producing quotidian fever and parasitaemia that can rise very rapidly within a single day, occasionally progressing to severe disease. This combination of Bornean travel history, malariae-like morphology, and rapid 24 hour parasite kinetics is the classic discriminator for knowlesi malaria and mandates PCR confirmation and treatment as for falciparum-equivalent risk. Why the other options are wrong: B. Plasmodium ovale malaria: Ovale has a distinct amoeboid trophozoite morphology with Schuffner dots and a 48 hour tertian cycle, and is geographically associated with West Africa, not Borneo, so it does not fit the morphology or kinetics described. D. Babesiosis: Babesia is a tick-borne piroplasm producing ring forms without pigment and without the true schizont or gametocyte stages seen in Plasmodium, and it is not endemic to Malaysian Borneo in the way P. knowlesi is. E. Acute toxoplasmosis: Toxoplasma does not appear as intraerythrocytic parasites on a thin blood film and does not cause a cyclical fever pattern, so it is incompatible with the film findings. A. African trypanosomiasis: Trypanosomes are extracellular flagellated organisms visible free in plasma, not within red cells, and the disease is confined to sub-Saharan Africa, not South East Asia. Key point: A malariae-like film plus rapid rise in parasitaemia over 24 hours in a traveller from Malaysian Borneo indicates P. knowlesi, not true P. malariae, and requires PCR confirmation and falciparum-level treatment urgency.
Reference: UK Malaria Treatment Guidelines (Lalloo DG et al., Journal of Infection 2016, current UK national guidance), https://www.journalofinfection.com/article/S0163-4453(16)00047-5/fulltext