[Studies on resistance of Schistosoma to praziquantel XVII Biological characteristics of praziquantel-resistant isolates of Schistosoma japonicum in mice].

OBJECTIVE: To investigate the biological characteristics of the praziquantel-resistant isolate of Schistosoma japonicum in mice, so as to explore the pathogenicity to definitive hosts and transmission intensity of the praziquantel-resistant isolate of S. japonicum .

METHODS: Mice were infected with the cercariae released from two praziquantel-resistant isolates and two praziquantel-susceptible isolates of S. japonicum . The mouse- Oncomelania hupensis snail-mouse cycle was established and maintained in the laboratory. The prepatent period of parasite eggs, egg production, egg distribution in mice, parasite susceptibility to mice and egg size were investigated in each parasite isolate.

RESULTS: The prepatent period of parasite eggs, egg counts in mouse feces, adult worms recovered from each mouse, egg counts in mouse tissues, egg counts in the mouse liver, and egg counts in intestine tissues were 36.1 d and 36.8 d ( t = 0.907, P = 0.372), 14.6 / 100 mg and 21.2 / 100 mg ( t = 2.946, P = 0.007), 20.5 and 25.1 worms per mouse ( t = 2.128, P = 0.042), 31 303 and 38 594 per paired adult worm ( t = 2.185, P = 0.04), 14 810 and 19 715 per paired adult worm ( t = 2.934, P = 0.007), and 16 493 and 18 879 per paired adult worm ( t = 1.044, P = 0.309) in the mice infected with Jiangsu praziquantel-susceptible and -resistant isolates of S. japonicum , respectively, and there were no significant differences between Jiangsu praziquantel-susceptible and -resistant isolates of S. japonicum in the length of paired adult worms ( t = 0.328, P = 0.744), female adult worms ( t = 0.386, P = 0.701) or male adult worms ( t = 0.332, P = 0.741). The prepatent period of parasite eggs, egg counts in mouse feces, adult worms recovered from each mouse, egg counts in mouse tissues, egg counts in the mouse liver, and egg counts in intestine tissues were 35.5 d and 35.6 d ( t = 0.169, P = 0.867), 13.3/100 mg and 18.9/100 mg ( t = 3.622, P = 0.001), 17.6 and 25.1 worms per mouse ( t = 3.153, P = 0.004), 30 932 and 53 903 per paired adult worm ( t = 3.865, P = 0.001), 12 307 and 26 363 per paired adult worm ( t = 4.388, P < 0.01), and 18 625 and 27 541 per paired adult worm ( t = 2.679, P = 0.012) in the mice infected with Hunan praziquantel-susceptible and -resistant isolates of S. japonicum , respectively, and there were no significant differences between Hunan praziquantel - susceptible and - resistant isolates of S. japonicum in the length of paired adult worms ( t = 0.853, P = 0.397), female adult worms ( t = 0.573, P = 0.569) or male adult worms ( t = 0.742, P = 0.461).

CONCLUSIONS: The praziquantel-resistant isolate of S. japonicum has a higher parasite egg production and more eggs deposited in the mouse liver than drug-susceptible isolate, suggesting that the praziquantel-resistant isolate of S. japonicum exhibits a greater pathogenicity to definitive hosts. In addition, more parasite eggs are detected in the feces of mice infected with the praziquantel-resistant isolate of S. japonicum relative to the drug-susceptible isolate, indicating that the praziquantel-resistant isolate of S. japonicum exhibits a greater transmissibility than the drug-susceptible isolate.