Bovine herpesvirus-1 and parainfluenza-3 virus interactions: clinical and immunological response in calves.

Calves infected with bovine herpesvirus-1 (BHV-1) or both BHV-1 and parainfluenza-3 virus (PIV-3) developed clinical signs including fever, cough, and nasal and ocular discharges. Animals infected with both viruses appeared more depressed and showed higher rectal temperature, while calves inoculated with PIV-3 alone had a very mild clinical disease. Both BHV-1 and PIV-3 were recovered from nasal secretions up to six to eight days postinoculation. However, the virus titers were lower in calves with mixed infection. An increase in serum antibodies to both BHV-1 and PIV-3 was detected by serum neutralization and enzyme-linked immunosorbent assay. Antibody responses were delayed and significantly lower in calves given mixed infection than in calves infected with a single virus. Interleukin-2 activity in cultures of lymphocytes from BHV-1 and BHV-1 plus PIV-3 infected calves was higher compared to control calves.