Which Plasmodium species are associated with relapsing malaria?

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

Answer: (A)

Relapsing malaria happens when dormant forms of the parasite hide in the liver and later reactivate to cause new blood-stage infections. These dormant liver stages, called hypnozoites, are formed by only a couple of Plasmodium species. When a person is infected with these two species, they can experience new febrile episodes long after the initial illness has resolved, due to reactivation of the hypnozoites. Therefore, relapsing malaria is associated with Plasmodium vivax and Plasmodium ovale.

Other species do not form hypnozoites in the liver, so they don’t cause relapses from hepatic dormancy. P. falciparum, P. malariae, and P. knowlesi produce ongoing blood-stage infections or recrudescence through other mechanisms, but not relapse due to latent liver forms. If relapse prevention is a clinical goal, treatment includes agents like primaquine (after checking G6PD status) to eradicate hypnozoites and prevent future relapses.