Plasmodium vivax relapse — DTM&H MCQ

Correct answer: A — Chloroquine followed by a 14-day course of primaquine

The correct answer is A, chloroquine followed by a 14 day course of primaquine. This patient has relapsing P. vivax malaria despite adequate chloroquine treatment, which reflects reactivation of dormant hepatic hypnozoites rather than blood stage treatment failure, since chloroquine and other blood schizonticides do not clear liver stages. UK malaria treatment guidelines state that the only currently effective drug for eradication of hypnozoites is primaquine, and that relapse occurs in more than 25 percent of vivax patients treated with chloroquine alone. Radical cure therefore requires a blood stage agent (chloroquine, continued or repeated) plus a full 14 day primaquine course, with G6PD status checked beforehand because of haemolysis risk. Fourteen days is the minimum proven duration; shorter courses are associated with higher relapse rates. Why the other options are wrong: C. Repeat chloroquine course alone: chloroquine clears erythrocytic parasites but has no activity against liver hypnozoites, so relapse will recur regardless of how many courses are given. D. Artemether-lumefantrine for 3 days: this ACT is a blood stage schizonticide, effective for acute non-falciparum or mixed infection, but like chloroquine it does not eradicate hypnozoites and therefore cannot prevent further relapse on its own. B. Mefloquine as a single dose: mefloquine is another blood stage agent with no hypnozoiticidal activity, and single dosing addresses only the current parasitaemia, not the underlying liver reservoir. E. Atovaquone-proguanil for 3 days: this combination is a blood stage treatment (and chemoprophylactic agent) with no activity against dormant liver forms, so hypnozoites persist and relapse continues. Key point: relapsing P. vivax after adequate blood stage therapy indicates hepatic hypnozoites, which only primaquine (after G6PD testing) can eradicate for radical cure.

Reference: UK malaria treatment guidelines 2016 (PHE/British Infection Association), Journal of Infection 2016;72:635-649, recommendations 19-22, https://www.journalofinfection.com/article/S0163-4453(16)00047-5/fulltext