SUMMARY: Twenty-three rat lung specimens collected in outbreaks of hemorrhagic fever with renal syndrome (HFRS) in three medical institutions were inoculated onto the VERO-E6 cell monolayers. After several blind passages, an agent growing serially in the cell cultures and reacting specifically with known HFRSpositive sera was isolated from two of these specimens. The two isolates were antigenically identical each other. The agent, named strain SR-11, was identified as the causative virus of HFRS by its antigenic identity with E6 cell-adapted HFRS virus, Hantaan 76-118 strain, and the specific reactions with sera from various HFRS cases.

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Horizontal transmission of HFRS virus to cagemates occurred from rats inoculated with the virus within 48 hours after birth, but not from those inoculated at 3 weeks of age.

Antigens of the viruses that cause hemorrhagic fever with renal syndrome (HFRS) and antibodies to these antigens were titrated in an immune adherence hemagglutination (IAHA) test and a CF test. Vero-E6 cells infected with the SR-11 strain of HFRS virus, an isolate from rats associated with a laboratory outbreak in Japan, and the 76-118 strain of Hantaan virus, the etiologic agent of Korean hemorrhagic fever, were used as antigens in the IAHA, CF, and indirect immunofluorescent antibody (IFA) tests. Sera from patients with different types of HFRS were tested against both strains of virus. Titers of antibody detected by the IFA test were similar for the two strains, but the IAHA test discriminated between antibodies to the two types of HFRS virus. Antigenic differences between HFRS viruses were suggested by the results of the IAHA test.

During the 1960's, 15 out of 89 rats (16.8%) captured in the port area and 6 out of 59 rats (10.2 YO) in the suburb of Tokyo were seropositive against Hantaan viruses.