A 45-year-old male migrant worker from Hunan presents with recurrent diarrhea for 2 years, occasionally with mucopurulent bloody stool. Physical exam: No abnormalities in heart/lungs. Liver palpable 3 cm below xiphoid, medium consistency; spleen palpable 3.5 cm below costal margin, firm. Laboratory tests: CBC shows WBC 7.6×10<sup>9</sup>/L (neutrophils 62%, eosinophils 10%). Stool analysis reveals mucopurulent bloody stool with RBC (++)/HPF and WBC (+)/HPF. The most likely diagnosis is: