Japanese river fever (Acute viral hemorrhagic fever) is an acute natural focal viral infectious disease caused by the tsutsugamushir virus, which is highly related to the hemorrhagic fever with renal syndrome virus. It is characterized by damage to the vessels of the microvasculature with hemorrhagic impregnation of tissues. The fever is acute with a pronounced cyclic increase in body temperature in patients up to 38-40 °C and above, intense intoxication, and hemorrhagic manifestations.