A 6-year-old child had acute onset of the disease that started catarrhal nasopharyngitis,2 days later the patient died. Autopsy of the body shows markedly plethoric and swollen pia mater that is soaked with thick turbid yellow – green fluid .The brain is swollen, the cerebellar tonsils are enlarged ,and there is a clearly visible ligature mark on the brain .The described changes are the characteristics of: