Experimentally induced infections bovine keratoconjunctivitis: effectiveness of a pilus vaccine against exposure to homologous strains of Moraxella bovis.

A study was conducted to determine whether vaccination with sonicated pili of Moraxella bovis would protect cattle from subsequent infection and disease when experimentally challenged by exposure to homologous cultures of M bovis. Some calves were intramuscularly inoculated 2 times with pili of M bovis suspended in water, and others were subcutaneously inoculated 2 times with pili of M bovis suspended in oil; 21 days were allowed between inculations. Controls were nonvaccinated calves. Fourteen days after the last inculation, all calves were exposed to virulent homologous cultures of M bovis. The results indicated that vaccination with sonicated pili of M bovis may induce protective immunity against homologous strain challenge exposure. Vaccines in oil that were injected subcutaneously protected to a greater extent than did vaccines in water that were injected intramuscularly. The development of inflammatory nodules at the site of inoculation was associated with resistance to infection and disease. Only 1 of the vaccinated calves that resisted disease lacked precipitating antibodies against sonicated pili at the time of the challenge exposure. This calf had antibodies 2 weeks later.