Infectious bovine keratoconjunctivitis: seasonal variation in cultural, biochemical and immunoreactive properties of Moraxella bovis isolated from the eyes of cattle

: The eyes of 20 young cattle were examined over an 18 month period in which 12 members of the group contracted infectious bovine keratoconjunctivitis (IBK). On each of 23 occasions cultural, biochemical and immunoreactive properties of up to 6 isolates of Moraxella bovis derived from each eye were determined. Relationships between the clinical response of eyes, phenotypic properties of M. bovis and annual variations in the level of solar ultraviolet radiation of 280 to 320nm wavelength were examined. M. bovis was isolated from all IBK‐affected and some unaffected eyes less than one month after the maximum annual level of the mean weekly UV radiation (2,840 mWh.m⁻².nm⁻¹) was recorded. A high proportion of M. bovis from IBK lesions were simultaneously active In haemolysis, agar corrosion, gelatin liquefaction and litmus milk peptonisation. Some of these characteristics showed marked dissociation despite consistent reactivity in the fluorescent antibody test, which had a sensitivity and specificity of 95%. Fall in the mean weekly level of UV radiation below 1,438 mWh.m⁻².nm⁻¹ in autumn was accompanied by healing of ulcers, persistent scar formation and a decline in the number of M. bovis isolated from affected eyes. A slower decline in the number of M. bovis isolated from apparently healthy eyes occurred in the winter and occasional fresh IBK lesions occurred. In spring, the rise in UV radiation above 1,438 mWh.m⁻².nm⁻¹ was accompanied by an increased frequency of isolation of M. bovis with all 4 characteristics, initially from scarred eyes, and later from those showing fresh ulcers. During late spring and the following summer, when mean weekly solar UV levels were in excess of 2,500 mWh.m⁻².nm⁻¹, increasing numbers of non‐haemolytic M. bovis were isolated, which were agar‐corroding and proteolytic, but were not associated with disease. Establishment, or re‐establishment, of M. bovis in the eye was associated with smooth colony morphology, followed by a gradual change to about 50% rough colony variants. This trend continued though winter, but as UV levels rose above 1,500 mWh.m⁻².nm⁻¹ during the second summer, smooth colony, non‐haemolytic types predominated. The possible use of such information in vaccination strategy against IBK is discussed.