Notes on Viral and Parasitic Infections (NUR1021 Lecture 7)

What is Cycle A: Host Ingestion?

Cycle A refers to a process where eggs, such as those from Ascaris (roundworm) and Trichuris (whipworm), are ingested by the host through contaminated food or water, hatch in the intestine, and develop into adult worms.

What is Cycle B: Skin Penetration?

Cycle B involves larvae, like those from Hookworms (Ancylostoma, Necator), penetrating the skin of the host, typically through bare feet, migrating through the bloodstream to the lungs, and then ascending to the throat where they are swallowed to reach the intestines.

What is Cycle C: Cyst Encystment in Animals?

Cycle C describes a process where the larval stage of helminths, such as Taenia (tapeworm), encysts in the tissues of intermediate hosts like pigs or cattle, and humans become infected by ingesting undercooked meat that contains these cysts.

What is Cycle D: Direct Penetration into Hosts?

Cycle D refers to a method where some helminths can directly penetrate the host's skin or mucous membranes without intermediaries, including transitions through larvae that develop directly into adults within the host.