A 34-year-old male visited Tajikistan. After return, he complains of fever up to 40°C which occurs every second day and is accompanied by chills, sweating. Hepatosplenomegaly is present. Blood test results: RBC- 3 × 1012/l, Hb- 80 g/l, WBC- 4 × 109/l, eosinophils -1%, stab neutrophils - 5%, segmented neutrophils - 60%, lymphocytes - 24%, monocytes -10%, ESR - 25 mm/h. What is the provisional diagnosis?