A 40-year-old male farmer presents with sudden onset of chills and fever for 4 days, accompanied by headache and generalized myalgia (most prominent in the gastrocnemius muscle). He visited in mid-August and was treated for 'common cold' without improvement. After 3 days, he developed petechiae, ecchymoses, and icteric sclera, prompting hospitalization. Examination: temperature 39.4°C, icteric sclera, inguinal lymphadenopathy, liver 2 cm below the costal margin, and marked tenderness in the gastrocnemius muscle. Lab results: WBC 25.2×10<sup>9</sup>/L (neutrophils 80%), platelets 25×10<sup>9</sup>/L, urinary protein (++), urinary RBC 20–30/HP, and total bilirubin 53.2 μmol/L. What is the most likely diagnosis?