HFRS is an acute febrile illness that was first recognized in the western world after a 1951 outbreak among U.S. troops stationed in Korea. This is followed by flushing, then petechiae. Thrombocytopenia, neutrophilia with left shift, atypical lymphocytes and hemoconcentration are common. There is acute renal failure, but the precise pathophysiologic lesion producing renal failure is uncertain. Mortality is usually from shock or hemorrhage.
Pulmonary edema is a frequent finding.
The common clinical features among the case-patients included a prodromal illness of fever, chills, and myalgia. The prodrome was followed by dyspnea, cough, thrombocytopenia, severe hemodynamic instability, neutrophilia with immature forms, atypical lymphocytes, elevated serum levels of lactate dehydrogenase. Transmission of virus from rodent carrier to humans occurs by ingestion of infected fecal matter, or inhalation of virus particles in aerosols of rodent urine. Infection may also be due to bites from infected rodents. It is possible that somewhere along the evolutionary history of the HFRS viruses a change occurred when it appeared in North America.