Parastrongylus cantonensis (syn. Angiostrongylus cantonensis)
(Nematoda, Strongylida, Metastrongyoidea)
Histological sections of worms in lungs of rats

Parastrongylus cantonensis, normally termed Angiostrongylus cantonensis, is an angiostrongylid that lives naturally in the pulmonary arteries of rats. First stage larvae migrate up the trachea and pass out with the feces. Molluscs, crustacea, and even land planaria serve as suitable intermediate hosts. The third stage larvae gain access to the definitive host either when the rat ingests contaminating larvae on food or when infected intermediate hosts are eaten. The third stage larvae migrate to the brain and spend about a month wandering in the meninges prior to entering the pulmonary circuit and maturing into adults. Infections in humans, an inappropriate host, may lead to serious and fatal eosinophilic meningioencephalitis. Ubelaker (1986, J. Parasitol. 72: 237-244) provides a useful synopsis on the taxonomy of the group.