Epidemiological survey of Corynebacterium equi infections on five Ontario horse farms.

Corynebacterium equi was cultured from manure or soil on five horse-breeding farms in Ontario at monthly intervals on three occasions during the summer of 1982. The organism was widespread. Contamination by C. equi of the loafing paddock and pasture areas was significantly greater in a farm established 30 years than in two established for four and six years and there was a significant correlation between the C. equi burden in stables, paddocks and pastures and the length of use of the five farms for horses. In all farms, numbers of C. equi in pasture soil exceeded numbers in fresh manure, suggesting that environmental multiplication of the organism might occur. A farm with an endemic C. equi pneumonia problem differed significantly from the other four farms, where disease was not endemic, in the larger number of C. equi isolated in the stable area. By contrast the farm with a C. equi pasture soil burden significantly heavier than on all other farms had no deaths due to C. equi pneumonia. There was a correlation (r = 0.78, p = 0.061) between the number of cases of C. equi pneumonia on the farms and numbers of C. equi in the area of the stables, but not on the paddocks or pastures. About two-thirds of randomly chosen isolates from the farms belonged to the three capsular serotypes most commonly found in pneumonic foals.