Plasmodium knowlesi malaria — DTM&H MCQ

Correct answer: E — Plasmodium-specific PCR

The correct answer is E, Plasmodium-specific PCR. This traveller has returned from Malaysian Borneo, a recognised hotspot for Plasmodium knowlesi, with daily (quotidian) fevers and band-form trophozoites in small red cells lacking Schuffner's dots, a picture that is morphologically indistinguishable from P. malariae on light microscopy. Unlike true P. malariae, P. knowlesi has a 24-hour asexual cycle, can produce parasitaemia rising rapidly to dangerous levels, and is a recognised cause of severe and fatal malaria in Southeast Asia, so species confirmation cannot be left to morphology alone. PCR is the only reliable method to distinguish P. knowlesi from P. malariae and P. falciparum and is required to guide correct treatment and risk stratification, particularly given the 5% parasitaemia already present. UK guidance on malaria diagnosis and management supports molecular confirmation whenever knowlesi is possible on epidemiological and morphological grounds. Why the other options are wrong: B. Repeat thick and thin film in 12 hours: Repeat microscopy will not resolve the morphological overlap between P. knowlesi and P. malariae and simply delays definitive species identification while parasitaemia can rise quickly. C. Rapid diagnostic test for HRP2 and pLDH: RDTs are validated mainly for P. falciparum and P. vivax detection; pan-specific pLDH lines cross-react poorly and inconsistently with P. knowlesi, making RDTs unreliable for confirming this species. A. Quantitative buffy coat analysis: This technique detects parasites via fluorescent staining of nucleic acid but gives no species-specific information and cannot distinguish knowlesi from malariae. D. Serology for Plasmodium antibodies: Serology reflects past exposure rather than current infection, has no role in acute diagnosis, and does not provide species-level discrimination needed for immediate management. Key point: Band-form trophozoites without Schuffner's dots in a returning traveller from Southeast Asia must trigger PCR to exclude P. knowlesi, which mimics P. malariae morphologically but behaves like a potentially severe daily-fever malaria.

Reference: UK Malaria Treatment Guidelines 2016 (Public Health England Advisory Committee on Malaria Prevention), Journal of Infection 2016;72(6):635-649, https://www.journalofinfection.com/article/S0163-4453(16)00047-5/fulltext