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 w ith Schistosoma japonicum, pigs were exposed to the cercariae of this paras ite in a highly endemic region of China. Five, 5-month-old pigs previously infected with S. japonicum (group A) and 10, schistosome-naive piglets (gro up B) were allowed on a pasture infested with Oncomelania snails for one tr ansmission period (approximately 5.5 months). All the piglets rapidly acqui red infection, and both groups remained infected throughout the study perio d. 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 i ntestinal and mesenteric vasculature, and egg-related pathology in the larg e intestine and liver. Major findings were exudative lesions connected with egg excretion in the intestine, and granulomatous obstruction of portal ve ins in the liver. Signs of granuloma modulation were found in the liver, bu t not in the intestine. In conclusion, the study showed that field exposure of pigs to S. japonicum for one transmission period resulted in clinical d isease and growth retardation in the youngest pigs, and significant patholo gy in both groups. Self cure, prominent in experimental porcine infections produced with single, high-dose inocula, was not induced in either group.