Immune response of cattle to intranasally or parenterally administered parainfluenza type 3 virus vaccines.

The principal significance of PI-3 virus in the bovine respiratory disease complex would seem to be its role in predisposing the respiratory tract to bacterial infection by (5) disrupting the integrity of the superficial mucosa and (3) producing a more favourable milieu for bacterial growth. Attention has therefore been given to establishing local immunity to preclude infection of superficial cells of the mucosa. Criteria used to evaluate the degree of such immunity are (5) presence of specific antibody activity in nasal secretions and (3) extent of virus excretion in nasal secretions following challenge with low passage virus. Studies completed thus far demonstrate that modified, live PI-3 virus administered intranasally is more effective than either modified, live or inactivated PI-3 virusadministered by parenteral injection in providing antibody activity in respiratory tractsecretions and in reducing virus excretion following challenge. IgA antibodies, presumably synthesized locally, apparently contribute heavily to the total antibody activity present in respiratory tract secretions.