Ovale malaria relapse — DTM&H MCQ

Correct answer: D — Plasmodium ovale malaria

The correct answer is D, Plasmodium ovale malaria. The blood film description of oval, enlarged erythrocytes with fimbriated (frayed) margins and Schuffner dots is the classic morphological signature of P. ovale infected red cells, and the eight month interval since travel to a West African endemic area fits the known pattern of delayed presentation. This delayed relapse occurs because P. ovale forms dormant liver hypnozoites that can reactivate months to years after the initial mosquito bite, unlike P. falciparum. UK treatment guidance identifies P. ovale (with P. vivax) as requiring radical cure with primaquine to eradicate these hypnozoites once glucose-6-phosphate dehydrogenase status is known, precisely because standard blood schizonticides do not clear the liver stage. Nigeria as the exposure country and the long latency both support ovale over the acute, non relapsing species. Why the other options are wrong: C. Acute schistosomiasis: causes eosinophilia, haematuria or Katayama fever, not fimbriated oval red cells with Schuffner stippling on a blood film, since Schistosoma does not parasitise erythrocytes. A. Babesiosis: parasites appear as ring forms or tetrads (Maltese cross) within red cells without Schuffner dots or fimbriation, and is tick-borne, usually with a history of exposure in the USA or Europe rather than Nigeria. E. Plasmodium knowlesi malaria: infects red cells of normal size, resembles P. malariae or falciparum morphologically, follows a rapid daily fever cycle, and has no hypnozoite stage, so it cannot explain an eight month latent relapse. B. Relapsing fever borreliosis: diagnosed by spirochaetes seen directly in the blood film, not intraerythrocytic parasites, and is transmitted by lice or ticks with a different fever pattern. Key point: fimbriated oval red cells with Schuffner stippling plus a relapse many months after leaving an endemic area point to P. ovale hypnozoite reactivation, requiring primaquine radical cure.

Reference: Lalloo DG, Shingadia D, Bell DJ, Beeching NJ, Whitty CJM, Chiodini PL; PHE Advisory Committee on Malaria Prevention in UK Travellers. UK malaria treatment guidelines 2016. J Infect. 2016;72(6):635-649. Available via PMC: https://pmc.ncbi.nlm.nih.gov/articles/PMC7132403/