Which Plasmodium species have latent hepatic hypnozoites that require primaquine for radical cure?

• A. P. falciparum
• B. P. vivax and P. ovale
• C. P. malariae
• D. P. knowlesi

Answer: (B)

Relapse in malaria comes from dormant liver-stage parasites, not from ongoing blood parasites. The human Plasmodium species that form these latent hepatic hypnozoites are P. vivax and P. ovale. Because these hypnozoites can reactivate weeks or months after the initial infection, eradicating both the blood stages and the dormant liver stages is needed for a true radical cure, and primaquine is the drug that specifically targets those liver forms. The other species—P. falciparum, P. malariae, and P. knowlesi—do not have a dormant hypnozoite stage in the liver, so they don’t require primaquine for radical cure. (Note: primaquine also has a role in treating certain gametocytes and must be used with caution in G6PD deficiency.)