Encapsulated egg deposition pattern of Schistosoma japonicum in the peritoneal cavity of mice.

Thirty-four albino mice were each exposed to 20 cercariae of Schistosoma japonicum by the intraperitoneal or percutaneous route and killed after 60-127 days. The peritoneal cavity of each mouse was flushed and worms in the portal vein system were perfused with citrated saline. After sedimentation, washings were examined microscopically. Mature worms were only found in the portal vein system. The worm recovery rate was much higher by percutaneous infection (61.2%) than by intraperitoneal (37.1%). The encapsulated egg granulomas were observed either in the peritoneal cavity or on the intestinal wall; the mean number of encapsulated egg granulomas was also higher in the former (1.6) than in the latter (0.6). The average number of eggs per granuloma was very similar by both routes (10.7 and 11.4). The mean size of encapsulated egg granulomas (529 microns) was increased correspondingly with the number of eggs (range 181-985 microns). The percentage of viable eggs within the granulomas in the peritoneal cavity (77%) was much higher than those on the intestinal wall (18%). Encapsulated egg granulomas were usually ovoid although some had an irregular shape.