Gnathostomiasis by Gnathostoma hispidum has occurred mainly in southern and western areas of Japan since 1980. In all cases, patients had eaten live loaches, freshwater fish imported from southeast Asia. Chief symptoms were creeping linear skin eruptions and eosinophilia, both of which disappeared in most patients within three months after the onset, and never recurred thereafter. In order to study how gnathostome larvae may survive and behave in humans, rats were infected with gnathostome larvae. Loaches were purchased in city markets in Fukuoka. Gnathostome larvae (G. hispidum) were recovered from the fish and fed to rats. They were killed at intervals of one and six months and one, two and three years postinoculation. Encysted larvae were found in the muscles of all rats and recovered larvae were all viable. A migrating larva was observed in muscle tissue from one rat that was killed three years postinoculation. In histological sections, walls around encysted larva were much thinner in a rat killed three years postinoculation than in a rat killed one month postinoculation.
