A patient with confirmed Plasmodium vivax malaria is treated with chloroquine but returns 3 weeks later with another febrile episode. Blood film again shows P. vivax rings. Which mechanism BEST explains this relapse rather than re-infection?
- A Persistent blood-stage schizonts resistant to chloroquine
- B Chloroquine-resistant P. vivax gametocytes surviving treatment
- C Reactivation of hepatic hypnozoites that were not targeted by chloroquine ✓
- D Immune evasion by P. vivax through antigenic variation of PfEMP1
Correct answer: C. Reactivation of hepatic hypnozoites that were not targeted by chloroquine
Explanation
P. vivax (and P. ovale) form dormant hypnozoites in the liver that can reactivate weeks to months after the primary episode, causing true relapse. Chloroquine eliminates blood-stage parasites but has no activity against hypnozoites. Primaquine (or tafenoquine) is required for radical cure to eliminate hypnozoites. Chloroquine-resistant P. vivax exists but is not the common explanation for early relapse in India. PfEMP1 antigenic variation is a feature of P. falciparum, not P. vivax.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.