In Vivo and in Vitro Properties of a Temperature Sensitive Mutant of Infectious Bovine Rhinotracheitis Virus

A temperature sensitive (ts) mutant RLB 106 was obtained from infectious bovine rhinotracheitis (IBR) virus. This mutant was genetically stable in vivo and in vitro. Intranasal instillation of io 4 2 TCID 50 into susceptible calves induced seroconversion in 12 of 13 animals. No fever or clinical signs of disease were seen although virus was recovered from nasal swabs of some calves for periods up to 13 days. High levels of interferon appeared in nasal secretions for several days. Transmission of virus from vaccinated to non-vaccinated calves occurred after periods of prolonged contact. Vaccinated calves, challenged with virulent virus, showed no signs of disease and excreted smaller amounts of virus for shorter periods of time than did a control calf. The RLB 106 strain appears to be a valuable candidate strain for a safe live vaccine against IBR.