Migration and development of the larvae of Gnathostoma nipponicum in the rat, second intermediate or paratenic host, and the weasel, definitive host.

Abstract

Migration and development of the larvae of Gnathostoma nipponicum in the rat as second intermediate or paratenic host and the weasel as definitive host were examined to clarify the pathogenesis in each animal. The advanced third-stage larvae (AdL3) given orally to rats remained in the stomach for 12 h post-infection (PI). After that, larvae transiently invaded various organs and finally moved into the muscle within 48 h. The percentage of eosinophils in the blood taken from the jugular vein of rats infected with AdL3 reached a maximum (about 6%) on day 20 PI and then decreased. IgG antibody titre for G. nipponicum measured by ELISA began to increase on day 5 PI and reached a plateau on day 20 PI. The AdL3 given orally to weasels moved from the stomach into the muscle and then increased in size. Half of them invaded the muscle within 5 days, whereas the majority of them invaded the muscles within 20 days PI. Morphology of worms which invaded the muscles indicated that they were still the larval form with three rows of hooklets on the head bulb. The larvae in the muscles developed to young adult worms with seven rows of hooklets on the head bulb within 40 days PI. These young adult worms invaded the oesophageal wall and formed a tumour within 60 days PI. It was presumed that worms invaded the oesophageal wall through the adventitia. Ferret and mink were shown to be potential final hosts of G. nipponicum.