Interdigital Dermatitis in Sheep
This necrotizing condition of the interdigital skin usually precedes or accompanies footrot. In Australia, it is considered to be caused by less virulent strains of Dichelobacter nodosus and is termed benign footrot (see Benign Footrot). Wet weather, damp pastures, and mud are predisposing factors. In milder cases, the interdigital skin is red, hairless, swollen, and moist. In severely affected cases, the integrity of the interdigital skin is compromised, exposing subcutaneous tissues. Suppuration and swelling of the deeper interdigital tissues may develop. Lameness can affect as many as 90% of sheep, and all four feet may be affected. The characteristic smell associated with virulent D nodosus infections is not present if D nodosus is not present. Healing is rapid when conditions dry out, but the disease may recur when conditions again become wet.
Because scald usually precedes a footrot outbreak, it is prudent to treat the condition as if it were footrot. Other diseases to consider in the differential diagnosis include dermatophilosis (strawberry footrot, see Dermatophilosis), which affects the hairy skin of the coronet and pastern. Viral diseases such as ulcerative dermatitis, contagious ecthyma, and foot-and-mouth disease may be excluded by flock history, clinical signs, electron microscopy, and serology. Currently, the treatment of choice consists of external application of 10% w/v zinc sulfate disinfectants via a footbath or aerosol.