Clearance and shedding of infectious bovine rhinotracheitis virus from the nasal mucosa of immune and nonimmune calves.

Infectious bovine rhinotracheitis virus was rapidly cleared from the nasal mucosa of calves after intranasal aerosol exposure. Nonimmune calves (experiment 1) cleared 10(9) plaque-forming units (PFU) of virus from the nasal mucosa in less than 4 hours and 10(6) PFU of virus in 1 hour. An eclipse phase followed the clearance of viral inoculum. Replicating virus was first detected at 9 hours. Viral titers increased stepwise until maximum was attained on postinoculation day 4. Virus persisted in the nasal mucus until day 12. Clinical signs of disease corresponded with the shedding of virus. In contrast to nonimmune calves, immune calves (experiment 2; same calves as in experiment 1, but 30 days after initial exposure) cleared 10(9) PFU of virus in 1 hour and 10(6) PFU of virus in less than 5 minutes. An abortive reinfection occurred after exposure of immune calves with 10(9) PFU of virus. Virus was first detected in these calves at 14 hours after exposure and was not detected beyond 24 hours after inoculation. Immune calves given 10(6) PFU of virus did not shed virus after clearance of inoculum. Clinical signs of infection were not observed in immune calves after viral challenge exposure. The date indicated that there was no detectable residual virus beyond 3 hours after the exposure.