Q.Describe the exo-erythrocytic (hepatic) cycle of Plasmodium vivax.

[!TLDR] The exo-erythrocytic cycle is the liver-stage multiplication of Plasmodium before it enters the blood.

Injected sporozoites invade liver hepatocytes and undergo schizogony to form cryptomerozoites; some sporozoites remain dormant as hypnozoites. This liver-stage cycle corresponds to the prepatent period, and precedes the parasite's entry into red blood cells. …

When an infective female Anopheles mosquito bites a person, it injects sporozoites into the bloodstream, which are carried to the liver rather than acting directly on red blood cells. There, the sporozoites invade hepatocytes (liver cells) and undergo asexual multiplication by schizogony, developing into a schizont that eventually releases numerous small daughter cells called cryptomerozoites — this entire phase, occurring outside red blood cells, is termed the exo-erythrocytic (or hepatic/pre-erythrocytic) cycle. The time taken for this liver-stage development, from the infective bite until parasites first appear in the peripheral blood, is called the prepatent period. A distinctive feature of Plasmodium vivax is that some of the sporozoites entering the liver do not develop immediately but instead remain dormant within hepatocytes as hypnozoites; these can reactivate weeks, months, or even years later, triggering a fresh round of schizogony and causing a relapse of malaria even after the original infection has apparently resolved. Only once crypto …

• Describing the exo-erythrocytic cycle as occurring in RBCs — 'exo-erythrocytic' specifically means OUTSIDE red blood cells, i.e., in the liver. …