What are malaria relapses caused by?

• A. Hypnozoite
• B. Merozoite
• C. Sporozoite
• D. Trophozoite

Answer: (A)

Malaria relapses come from a dormant liver-stage parasite called a hypnozoite. After the initial infection is resolved, these hypnozoites can reactivate weeks or months later, releasing merozoites that invade red blood cells and restart the blood-stage cycle with new symptoms. This dormant liver form is characteristic of P. vivax and P. ovale.

Merozoites are the blood-stage forms that invade red blood cells during an active infection. Sporozoites are the form introduced by mosquitoes that initially infect the liver, and trophozoites are the feeding stage inside red blood cells. None of these themselves explain relapse; relapse is specifically due to the dormant liver hypnozoites.