A 28 y.o. patient who has no permanent residence was admitted to the hospital with preliminary diagnosis "influenza", on the 5-th day of disease there are appeared maculopapular and petechial rash on his body and internal surfaces of his extremities. Body temperature is 41°C, euphoria, hyperemic face, scleras reddening, tongue tremor, tachycardia, splenomegaly, excitement. What is the most probable diagnosis?