Question

Describe the life cycle of Plasmodium with a diagram.

Hint:

Two hosts: human (asexual schizogony) and Anopheles (sexual sporogony); periodic fever from RBC rupture.

Answer 1

Step 1: Identify the two hosts:
Plasmodium, the malaria-causing parasite, completes its life cycle in two hosts: the female Anopheles mosquito (the definitive host, where the sexual phase/sporogony occurs) and humans (the intermediate host, where the asexual phase/schizogony occurs).

Step 2: Trace the cycle in the human host:
An infected mosquito injects sporozoites into the human bloodstream during a bite; sporozoites first infect liver cells (exo-erythrocytic schizogony, producing merozoites), which are then released and infect red blood cells (erythrocytic schizogony); the RBCs eventually rupture synchronously, releasing more merozoites plus a toxic substance called haemozoin, which causes the classic periodic chills and high fever of malaria.

Step 3: Trace the cycle in the mosquito host:
Some merozoites in the RBCs develop into gametocytes instead of dividing further; when a mosquito bites an infected person, it ingests these gametocytes, which mature into gametes in the mosquito's gut, fuse to form a zygote, develop into a motile ookinete, then an oocyst on the gut wall, which eventually releases sporozoites that migrate to the mosquito's salivary glands, ready to infect the next human host.

Final Answer:
Plasmodium alternates between human (asexual, liver then RBC schizogony causing periodic fever) and female Anopheles mosquito (sexual, gametocyte to zygote to oocyst to sporozoite) hosts, transmitted by the mosquito's bite each time (a diagram would show this cyclical transfer with an arrow from mosquito salivary gland into human blood, and an arrow from human blood gametocytes back into the mosquito gut).