Infectious bovine keratoconjunctivitis: enhancement of Moraxella bovis pili immunogenicity with diphtheria-tetanus toxoids and pertussis vaccine.

A study was conducted to determine whether diphtheria-tetanus-toxoids and pertussis vaccine (DPT) would enhance the immunogenicity of homologous Moraxella bovis pili fractions. Thirty-six calves were divided into 4 groups (I, II, III, and IV) of 9 calves each. Calves in group I were not vaccinated and served as controls. Calves in group II were vaccinated with pili fractions only. Calves in group III were vaccinated with DPT only. Calves in group IV were vaccinated with DPT and pili. Vaccination consisted of 2 inoculations, 21 days apart. Fourteen days after the last vaccinal inoculation was done, the eyes of all calves were exposed to a hemolytic homologous strain of M bovis. The percentage of eyes with disease was significantly less in calves given DPT and pili (P less than 0.001) and calves given pili only (P less than 0.05) than in calves given DPT only or nonvaccinated calves. The lesions were less severe in calves vaccinated with pili only than in calves not vaccinated with pili. Serologic results also showed a positive relationship between the development of serum antibodies against pili and immunity. The results indicate that DPT enhanced the immune response and if used as an adjuvant, might be useful in the development of a vaccine against infectious bovine keratoconjunctivitis.