Abstract
Summary
1. A modified IBR virus was produced by rapid passages and terminal dilutions in bovine embryo kidney tissue culture. Its avirulence was demonstrated by intramuscular and intranasal inoculation of susceptible cattle. 2. Modified virus inoculated intramuscularly elicits an immune response which protects cattle against challenge with virulent virus. 3. The virus did not spread from intramuscularly-inoculated cattle to susceptible contacts, and could not be reisolated from blood or nasal washings of vaccinated cattle. 4. This modified virus prepared in tissue culture can be successfully lyophilized, thus allowing its use as a vaccine for prevention of IBR disease.
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