Schistosoma japonicum: interactions of successive infections in pigs and mice using polymerase chain reaction-based identification of individual worms

The study reported here investigated acquired resistance of mice and pigs t o challenge-infections with Schistosoma japonicum. Two morphologically indi stinguishable isolates of the parasite (fram the Anhui and Zhejiang provinc es of China), which could be typed by polymerase chain reaction-linked rest riction fragment length polymorphism analysis (PCR-RFLP), were used for the infections. In two parallel infection studies, 60 female outbred NMRI mice and 29 Danish Landrace/Yorkshire/Duroc crossbred pigs were used. Two of th e groups received a primary infection with either the Anhui or the Zhejiang isolate, respectively. The remaining groups received a primary infection w ith the Zhejiang isolate and challenge-infections with the Anhui isolate at either week 2, 3, 4 or 6 post primary infection. The results of the study indicated that both mice and pigs are partially resistant to challenge-infe ction from week 4 post primary infection. Resistance appeared to decrease i n pigs 6 weeks after primary infection, while it remained effective in mice . These results suggest that the mechanism responsible for acquired resista nce in mice and pigs may not be the same and support the theory that worm b urdens in pigs receiving repeated infection are in a balance between acquis ition and loss of worms. (C) 2000 Australian Society for Parasitology Inc. Published by Elsevier Science Ltd. All rights reserved.