A 40-year-old male fisherman, residing in a schistosomiasis endemic area with a habit of drinking untreated water, presents with 3 weeks of continuous high fever (40°C, remittent type), abdominal distension, and 2-3 mucoid stools daily. Physical exam reveals liver 2 cm below the costal margin and spleen 1 cm below the costal margin. Lab results show WBC count 3.0×10<sup>9</sup>/L (neutrophils 55%, lymphocytes 45%), eosinophil count zero, and cough. The most likely diagnosis is: