Artemisinin-resistant falciparum malaria — DTM&H MCQ

Correct answer: C — Reduced artemisinin susceptibility requiring expert follow-up

A) Reduced artemisinin susceptibility requiring expert follow-up is correct. Artemisinins normally clear detectable parasitaemia by day 3, so a persistent positive blood film at day 3 despite supervised, correctly dosed ACT is the recognised marker of partial artemisinin resistance, which is well established in the Greater Mekong subregion including the Cambodia-Thailand border. This resistance is linked to PfKelch13 mutations causing delayed ring-stage clearance rather than outright treatment failure, which is why the patient can still be clinically improving while parasites remain visible. UK guidance for returning travellers from this region specifically flags delayed clearance as a trigger for expert advice (for example from the UK malaria reference laboratory or an infectious diseases/tropical medicine specialist) and closer follow-up to confirm eventual clearance and exclude true recrudescence. Why the other options are wrong: E. Incorrect diagnosis of vivax malaria: the case specifies falciparum malaria, confirmed presumably by blood film or PCR; vivax does not explain a rising or persistent asexual falciparum parasite count on treatment. A. Relapse from dormant hypnozoites: hypnozoites occur only in P. vivax and P. ovale, not P. falciparum, so this mechanism cannot apply here, and true relapse would occur weeks to months later, not on day 3 of the index treatment. B. Expected clearance after any ACT: normal ACT pharmacodynamics clear parasitaemia within 72 hours in fully susceptible infections, so persistence at day 3 is abnormal and cannot be dismissed as expected. D. New infection from Anopheles in the UK: competent Anopheles vectors are not established transmitting malaria in the UK, making autochthonous reinfection essentially impossible within days of return. Key point: day 3 parasite positivity after supervised ACT in a traveller from the Greater Mekong subregion signals possible artemisinin partial resistance and warrants specialist review rather than reassurance.

Reference: GOV.UK / UK Health Security Agency (formerly PHE Advisory Committee on Malaria Prevention), 'Management of treatment failure (recrudescence) in falciparum malaria', UK malaria treatment guidelines: https://www.gov.uk/government/publications/management-of-treatment-failure-recrudescence-in-falciparum-malaria/management-of-treatment-failure-recrudescence-in-falciparum-malaria