An outbreak of severe digital disease in feedlot cattle

One quarter of all the cattle on a feedlot unit containing 400 animals became affected with a sudden-onset lameness over a period of six weeks from the beginning of March 1995. The condition was seen in bulls, heifers and bullocks. Typically, one or two cattle in a pen of 20 presented with severe lameness; within 72 hours up to half of the cattle in the pen were similarly affected. The first case to occur were treated with topical and systemic oxytetracyclines, tylosin and penicillin and streptomycin. However, the response to treatment was poor and because of rapid weight loss, a decision was made in mid-March to cull all affected cattle as they presented. The condition in any particular animal usually involved a single Limb, either fore or hind, and affected animals exhibited a marked reluctance to bear weight on the limb involved. There was swelling of the coronary band, fissuring of the interdigital skin and development of granulation tissue within the fissures. Spirochaetes were demonstrated on examination of direct smears made from the lesions and Bacteroides melaninogenicus was isolated on cultural examination. The histopathological characteristics associated with the condition included a widespread keratinocyte degeneration within which were present variably-sized bright eosinophilic intracytoplasmic inclusion bodies. Ultrastructural examination of these inclusions suggested that they consisted of amorphous intracytoplasmic debris; no viral particles could be identified. However, numerous spirochaetes were present within the cytoplasm of affected keratinocytes. Attempts to demonstrate virus on electron microscopic examination of negatively-stained preparations made from lesions and attempts to culture virus from all lesions were all unsuccessful. The presence of numerous intracellular spirochaete-like organisms suggests a likely role in the aetiology of this condition.