A 28 y.o. patient without permanent residence was admitted to the hospital with the preliminary diagnosis influenza. On the fith day of illness he got a maculopapular petechial rash on his body and internal surfaces of extremities. Body temperature is 41°C, euphoria, face hyperemia, sclera reddening, tongue tremor, tachycardia, splenomegaly, excitement. What is the most probable diagnosis?