To evaluate the efficacy of a recombinant Moraxella bovis
pilin-M. bovis
cytotoxin subunit vaccine to prevent naturally occurring infectious bovine
keratoconjunctivitis (IBK; pinkeye), a randomized, blinded, controlled field trial was conducted during summer 2005 in a northern California herd of beef cattle. One hundred and one steers were vaccinated with
ISCOM matrix (adjuvant control), recombinant M. bovis
cytotoxin carboxy terminus+ISCOM matrix (MbxA), or recombinant M. bovis
pilin-
cytotoxin carboxy terminus+ISCOM matrix (
pilin-MbxA); calves received secondary vaccinations 21 days later. Calves were examined once weekly for 18 weeks for the development of corneal
ulcers associated with IBK. Overall, the
pilin-MbxA vaccinated group had the lowest overall cumulative proportion of ulcerated calves. Calves that received MbxA, whether alone or with
pilin had significantly higher M. bovis
cytotoxin serum neutralizing titers as compared to control calves. Results of ocular cultures suggested that vaccination with an M. bovis
antigen affected organism type isolated from an
ulcer: M. bovis was cultured more often from the eyes of control calves than from the eyes of calves vaccinated with MbxA and
pilin-MbxA. In addition, vaccination of calves with MbxA and
pilin-MbxA resulted in a higher prevalence of Moraxella bovoculi sp. nov. in ocular cultures. While no significant difference was observed between a
cytotoxin versus pilin+cytotoxin
vaccine against IBK, the reduced cumulative proportion of IBK in the
pilin-
cytotoxin vaccinated calves suggests it may provide an advantage over a
cytotoxin vaccine alone. Efficacy of an M. bovis
vaccine may be reduced in herds where IBK is associated with M. bovoculi sp. nov.