Fig. 1. Hookworm life cycle.

Infective larvae (iL3) survive in warm humid environments. Upon contact with the human host, they penetrate the skin (1), migrate through the circulatory vasculature to the lung (2), where they molt, and are carried up by the trachea by the host muco-ciliary ladder and swallowed. Larvae are retained in the small intestine (3) where they develop to the adult stage, mate, and produce eggs. Eggs are released with the feces into the environment, they hatch, develop through three stages to the infective L3. This review will focus on the immune responses elicited in the skin, lungs and intestine by this and related parasites.