Bovine infectious keratoconjunctivitis: carrier state of Moraxella bovis and the development of preventive measures against disease.

Bovine infectious keratoconjunctivitis, which is caused by Moraxella bovis, occurs perennially in all cattle-raising areas. Disease may occur any time during the year but manifests itself often during summer when disease-enhancing factors such as ultraviolet radiation and fly population are increased. Although some recent research findings indicate that cattle can be immunized against the disease, many problems have to be overcome before the cattle industry can benefit from such immunization. Some pressing problems relate to lack of cross-protection between vaccines of different strains of M bovis, resistant or resilient carrier states, and how these factors affect vaccination regimens undertaken. Though cattle vaccinated with 1 strain are somewhat protected against subsequent challange by the same strain, protection against heterologous strains has not been demonstrated. In most herds, cattle harbor M bovis, and these carriers may serve as a source of infection.