The effect of a low level primary Schistosoma japonicum infection on establishment of a challenge infection in pigs

The aim of the study was to investigate the effect of a low-level primary infection of Schistosoma japonicum on a challenge infection in pigs. Groups of pigs were given either light or heavy primary infections and heavy challenge infections 14 weeks later. One group of pigs served as a challenge control group. Challenge infection superimposed on the heavily infected pigs did not result in increased worm burden, faecal and tissue egg counts or IgG levels. In contrast, the challenge infection established fully when superimposed on the light primary infections. However, neither faecal egg counts nor the IgG levels increased, and the amount of liver pathology, as judged by septal fibrosis, did not increase either, as compared to the challenge control group. These results suggest that pigs are not able to mount an effective anti-worm response to reinfection when the primary infection is low. However, some modulation of the infection takes place, possibly as a result of an anti-embryonation effect. Collagen content in the liver was found to be relatively insensitive as a marker for liver pathology, as judged using portal and septal fibrosis as a criteria.