Experimentally induced infectious bovine keratoconjunctivitis: resistance of vaccinated cattle to homologous and heterologous strains of Moraxella bovis.

In studies to determine whether vaccination with one strain of Moraxella bovis would protect against challenge with virulent homologous or heterologous strains, calves were intramuscularly inoculated 3 times with formalin-killed M bovis, with 14 days between inoculations. Fourteen days after the 3rd vaccinal dose was given, all calves were exposed to homologous or heterologous virulent cultures of M bovis. The results indicated that vaccination with one strain of M bovis may induce protective immunity against homologous and heterologous challenge exposure; however, because vaccinated cattle resisted infection and disease produced by a homologous strain to a greater extent than they resisted those produced by heterologous strains, polyvalent vaccines or highly immunogenic common antigens may be needed to protect cattle against the numerous strains they might encounter under natural field conditions. There was minimal correlation between the presence of precipitating antibodies against the heterologous strains and the establishment of infection and disease.