The Route of Migration of the Larva of Paragonimus westermani in the Final Hosts

Abstract

The course of infection and migration of Paragonimus westermani was studied in cats and rats with the Evans-blue technique to make it easier to find the lesions and recover the worms. The cats were divided into two groups, one under and one over 350 g. Cats were given 50 metacercariae each and rats 20. Cats were sacrificed and examined periodically from a half hour to 14 days after infection; rats from one-half hour to 180 days. From 40% to 60% of the worms fed were recovered at each examination. Worms penetrate the intestinal wall within 30 to 60 min after feeding, and reach the abdominal cavity in from 3 to 6 hr. The worms then penetrate the abdominal wall, whence, after having made some growth, they re-enter the abdominal cavity in from 6 to 10 days, and migrate through the diaphragm to the pleural cavity and lungs. The period of residence in the body wall coincides with that when earlier workers were unable to find the worm. The pattern of migration and development differs somewhat in cats above and below 350 g, and in rats. The rat is an unfavorable host and will not support maturity of the parasite, although many of the worms wander in its tissues indefinitely. S. Yokogawa (1915, 1916, 1919, 1921) was the first to point out the route of migration to the lungs of larvae of Paragonimus westermani after penetration of the intestinal wall of the final host. This route was accepted by Nakagawa (1915a, b) and Ando (1915). According to Yokogawa the metacercaria given orally excysts in the upper or middle parts of the small intestine, penetrates the intestinal wall, wanders about in the abdominal cavity for about 2 weeks, and then migrates upwards through the diaphragm to the pleural cavity. It finally arrives in the lungs where it settles down and forms its worm cyst. Sixty to 70 days after infection the larva reaches maturity in the worm cyst. S. Yokogawa and Ando fed metacercariae to experimental animals and tried to follow the course of migration by collecting the worms from the intestinal wall, abdominal and pleural cavities, and various organs. Few worms were recovered during the Received for publication 24 April 1961. * The research reported in this document has been made possible through the support and sponsorship of the U. S. Department of Army through its Far East Research Office, and also was supported in part by a Scientific Research Grant from the Ministry of Education in Japan. t The material covered in this paper has already been published in Japanese journals in Japanese (Yokogawa, 1960; Yokogawa and coworkers, 1958, 1959a, b). period from the 1st day to the 2nd week after infection, a difficulty that previous investigators attributed to the small size of the young