A 40-year-old male fisherman, residing in a schistosomiasis endemic area with a habit of drinking untreated water, presents with persistent high fever (40°C, remittent type) for 3 weeks, abdominal distension, and mucoid stools (2-3 times/day). Physical examination reveals liver 2 cm below the costal margin, spleen 1 cm below the costal margin, WBC count 3.0×10<sup>9</sup>/L (neutrophils 55%, lymphocytes 45%, eosinophil count zero), and cough. Right lower abdominal guarding and loss of liver dullness are noted. What is the most urgent management?