Figure 1. The life cycle of Angiostrongylus cantonensis.

Rats, as definitive hosts, acquire A. cantonensis when the third-stage infective larvae are ingested. The larvae enter the bloodstream and reach the central nervous system (CNS), where they undergo two molts to become adult worms in two weeks. The adult worms migrate to the pulmonary arteries and develop to sexual maturity and lay eggs (A). An adult female nematode produces ~15,000 eggs daily. Eggs are carried to the capillaries and break into the air spaces where they hatch. The first-stage larvae (the juveniles) migrate up the trachea and are swallowed, and are excreted out with the feces (B). Approximately six to eight weeks after infection, the rat excretes the first-stage larvae. The larvae in feces are swallowed by intermediate host molluscs (snails or slugs) and develop into third-stage (infective) larvae in 12 days (C). The third-stage larvae could be transmitted to the paratenic hosts such as shrimps, land crabs and predacious land planarians (D) or contaminate vegetables (E). Humans occasionally acquire A. cantonensis when they eat snails, slugs and sometimes, land crabs, frogs, freshwater shrimps, containing infective larvae, or contaminated vegetables. The larvae are digested from tissues and enter bloodstream in intestine (F). The larvae finally reach central nervous system (CNS) and cause eosinophilic meningitis (G) or move to eye chamber and cause ocular angiostrongyliasis.

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