Malarial relapse is seen in –
**Core Concept**
Malarial relapse is a clinical phenomenon where the parasite reappears in the blood after a period of apparent recovery, due to the reactivation of latent parasites that have sequestered in the liver. This occurs in Plasmodium vivax and Plasmodium ovale infections, as these species can form hypnozoites, a latent stage of the parasite that can reactivate months or years after the initial infection.
**Why the Correct Answer is Right**
Malarial relapse is a result of the reactivation of hypnozoites in the liver, which are responsible for the recrudescence of the infection. Hypnozoites can remain dormant for years, and their reactivation is often triggered by factors such as stress, pregnancy, or certain medications. The reactivation of hypnozoites leads to the production of new parasites that eventually enter the bloodstream, causing a relapse of the infection.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because P. falciparum does not form hypnozoites and therefore does not cause relapse.
**Option B:** This option is incorrect because P. malariae can cause long-term infections, but it does not typically cause relapse in the same way that P. vivax and P. ovale do.
**Option C:** This option is incorrect because P. knowlesi is a zoonotic species that primarily infects macaques, and it does not typically cause relapse in humans.
**Clinical Pearl / High-Yield Fact**
It's essential to note that P. vivax and P. ovale relapses can occur months or even years after the initial infection, making it crucial to consider this possibility in patients with a history of malaria exposure.
**Correct Answer: D. Plasmodium vivax and Plasmodium ovale.**