Pathology and course of natural Schistosoma japonicum infection in pigs: results of a field study in Hubei province, China.

In order to obtain information on the natural course of porcine infection with Schistosoma japonicum, pigs were exposed to the cercariae of this parasite in a highly endemic region of China. Five, 5-month-old pigs previously infected with S. japonicum (group A) and 10, schistosome-naïve piglets (group B) were allowed on a pasture infested with Oncomelania snails for one transmission period (approximately 5.5 months). All the piglets rapidly acquired infection, and both groups remained infected throughout the study period. Group B showed fever, diarrhoea and anorexia in the early egg-excretion phase, and marked growth reduction. In both groups, post-mortem examination revealed live schistosomes and lesions associated with dead worms in the intestinal and mesenteric vasculature, and egg-related pathology in the large intestine and liver. Major findings were exudative lesions connected with egg excretion in the intestine, and granulomatous obstruction of portal veins in the liver. Signs of granuloma modulation were found in the liver, but not in the intestine. In conclusion, the study showed that field exposure of pigs to S. japonicum for one transmission period resulted in clinical disease and growth retardation in the youngest pigs, and significant pathology in both groups. Self cure, prominent in experimental porcine infections produced with single, high-dose inocula, was not induced in either group.