A patient complains of skin painfullness and reddness of the right gastrocnemius muscle. Objectively: body temperature is 38,5°C, enlarged and painful inguinal lymph nodes on the right. Skin of extremity is edematic, hyperemic, covered with eruption in form of vesicles containing dark fluid; its palpation is painful. There is distinct border between normal and hyperemic skin. What is the most probable diagnosis?