Summarize the Trichinella spiralis life cycle and the typical route of human infection.

• A. Ingesting undercooked meat containing nurse larvae; larvae mature in the small intestine to adults; newborn larvae disseminate to striated muscles and form cysts
• B. Ingesting contaminated water with eggs that hatch in stomach
• C. Bite by infected insects transmitting larvae
• D. Inhalation of spores from soil

Answer: (A)

Trichinella spiralis is acquired when you eat undercooked meat that contains larval cysts. Once the cysts reach the small intestine, the larvae hatch and mature into adults. The adult females then produce newborn larvae that travel through the bloodstream to striated muscles, where they invade muscle fibers and form nurse cells that encase the larvae as cysts. This cycle can continue within the same human host and explains the muscle symptoms often seen in trichinellosis. The other described routes—ingesting eggs in contaminated water, infection by a biting insect, or inhaling spores from soil—do not apply to this parasite’s transmission and life cycle.