| Research Abstract |
The mode of HFRS virus transmission among rodents was examined by comparing the results of epidemiological surveys of urban rats in endemic areas and experimental infection of laboratory rats. The results are as follows.
1) The urban rats in the endemic focus have shown the age-dependent acquisition of infection. HFRS virus was mostly isolated from lung tissue in adult rats showing high antibody titers.
2) A total four sero-positive small field mice, two Clethrionomys rufocanus bedfordiae, one Apodemus argenteus hokkaidi and one Apodemus speciosus ainu, were detected around the endemic focus indicating an evidence of transmission of HFRS virus from the infected urban rats to indigenous field mice.
3) Two strains of HFRS virus from Rattus, SR-11 and KI-262, showed identical antigenicity but deferred in virulence against newborn rats. SR-11 strain isolated from a laboratory rat developed clinical signs and died at about 18 days after inoculation. KI-262 strain from an urban rat in an endemi
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c focus, did not show any clinical signs. Necrosis of neurons in the brain tissue occurred in the rats infected with SR-11, while it was mild in the animals infected with KI-262.
4) When rats-were inoculated with SR-11, sero-conversion rate was almost similar in newborn and adult rats regardless of inoculation routes.
5) IgG antibody was transferred from immune dams to their offspring prenatally as well as postnatally. IgG antibody was detected in the fetus sera. In newborn rats, maternal IgG antibody reached a peak titer at two weeks after birth, then declined and disappeared at about 8 weeks of age. The protective effect of maternal antibody remained in 10 week-old rats.
6) Antibody dependent enhancement (ADE) of the infection of HFRS virus was studied using macrophage-like cell lines. ADE of the infection occurred with monoclonal antibodies (MAbs) to both Gl and G2 envelope glycoproteins, but not with MAbs to nucleocapsid protein. Antigenic determinants related to hemagglutination and virus neutralization were found to cause ADE of the infection Less
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