Five immunologically identical strains of virus have been isolated from naturally and experimentally produced cases of ephemeral fever, by the intracerebral inoculation of suckling mice with infective buffy coat suspension. The prototype strain was found to be DCA and ether sensitive. Specific neutralizing antibodies could be demonstrated in the convalescent sera of both naturally and experimentally infected cattle. Serial passage of the virus in suckling mice resulted in a very rapid loss of pathogenicity for cattle with a corresponding loss of immunogenicity.
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