Infectious bovine keratoconjunctivitis: subconjunctival administration of a Moraxella bovis pilus preparation enhances immunogenicity.

To compare the immune response elicited by 3 routes of vaccination, 36 calves were randomly allotted to 4 groups of 9 calves each. Group I was vaccinated subconjunctivally only. Group II was vaccinated concomitantly, both subconjunctivally and in the dewlap. Group III was vaccinated in the dewlap only. Group IV was not vaccinated and served as a virulence control for the Moraxella bovis culture. Calves in groups I, II, and III were given 2 inoculations with 14 days between inoculations. Twenty-one days after the last inoculation, the ventral conjunctival sac of all calves was instilled with cells of a virulent M bovis strain. After challenge exposure, all vaccinated calves (groups I, II, and III) had evidence of enhanced resistance, compared with the nonvaccinated calves. The highest to lowest gradients of immune responsiveness were: Group I greater than or equal to group II greater than group III greater than group IV. When immune criteria, such as the percentage of diseased eyes, the mean duration of infection, the severity of corneal lesions, and the serologic response were compared, groups I and II were significantly (P less than 0.05) more resistant to challenge exposure than were groups III and IV. Group III was significantly (P less than 0.05) different from group IV in severity of lesions and in serologic response. Also, the mean duration of infection was shorter, and the percentage of diseased eyes was less in group III than in group IV (P greater than 0.10). Group I was more resistant than was group II (P less than 0.10).(ABSTRACT TRUNCATED AT 250 WORDS)