A 45-year-old male with a 10-year history of chronic schistosomiasis presents with hepatomegaly (liver palpable 1 cm below costal margin, 4 finger-breadths below xiphoid), splenomegaly reaching the umbilicus, positive serum Schistosoma japonicum antibody, and elevated ALT (100 U/L) without jaundice. The most effective treatment for the pathogen is: