Falciparum malaria with pfhrp2 deletion — DTM&H MCQ

Correct answer: A — Confirm with expert microscopy or a non-HRP2 molecular assay

The correct answer is A, confirm with expert microscopy or a non-HRP2 molecular assay. UK malaria treatment guidelines state the optimum diagnostic procedure is examination of thick and thin blood films by an expert to detect and speciate parasites, with rapid diagnostic tests supporting rather than replacing microscopy. This patient has classic severe falciparum features (rigors, thrombocytopenia, splenomegaly, ring forms on film) yet a negative HRP2 antigen test, a recognised pattern seen with pfhrp2/pfhrp3 gene deletions causing false-negative HRP2-based RDTs despite true parasitaemia. Given strongly suspicious clinical and microscopic findings, the diagnosis cannot be excluded on RDT alone; a second expert film reading or a non-HRP2 test (pLDH RDT or PCR) is needed to confirm species and parasitaemia. This exact discordance has been documented in imported cases in the UK and Ireland, confirming that HRP2 alone is unsafe in travellers or migrants from endemic areas. Why the other options are wrong: B. Accept the rapid test as excluding falciparum malaria: ignores a discordant, highly suspicious film and known pfhrp2/3 deletion false negatives; risks fatal delay in treating severe malaria. D. Perform serology for malaria antibodies: reflects past exposure, not acute infection, and is far too slow and irrelevant for an acutely febrile patient with parasites already seen. C. Send urine microscopy for Schistosoma haematobium: no haematuria or supporting history, and does not explain the ring forms or thrombocytopenia already identified. E. Request Weil-Felix testing for rickettsial infection: rickettsiae do not produce ring forms on a film, and Weil-Felix is an outdated, insensitive test not used in UK practice. Key point: a negative HRP2 RDT does not exclude falciparum malaria when the film shows ring forms and clinical features fit, because pfhrp2/3 deletions cause false negatives, so expert microscopy or a non-HRP2 assay must confirm the diagnosis.

Reference: UK malaria treatment guidelines 2016 (Lalloo DG et al., Journal of Infection 2016; endorsed by PHE/UKHSA), Diagnosis section: 'The optimum diagnostic procedure is examination of thick and thin blood films by an expert to detect and speciate the malarial parasites.' https://www.journalofinfection.com/article/S0163-4453(16)00047-5/fulltext