Infectious bovine keratoconjunctivitis: evidence for general immunity

A study was conducted to determine whether acquired immunity to Moraxella bovis during episodes of infectious bovine keratoconjunctivitis (IBK) was local or general. Twelve calves (principals) were exposed to M bovis in the left eye by conjunctival sac instillation on day 1 and in both eyes on day 21. Six calves exposed in both eyes at day 1 and six others exposed at day 21 served as controls. The mean duration of infection in the right eyes of principal calves was significantly less (P less than 0.001) than that in the left eyes of principal calves, as well as those of the control calves. There were no significant differences (P less than 0.2) in the durations of infection between the 2 groups of the control calves or the duration of infection in the left eyes of principal calves. Five of 6 calves (7 of 12 eyes) in the day 1 controls and 4 of 6 calves (7 of 12 eyes) in the day 21 controls developed IBK. Ten of 12 of the principals developed IBK in the left eye when exposed on day 1, but only 1 of 12 principals developed IBK in the right eye when exposed on day 21. It was concluded that the resistance to infection after initial infection is probably due to a generalized immune response, rather than to a localized response.