Common clinical signs associated with cellulitis include painful swelling, heat, and lameness of the affected leg. | Photo: Courtesy Ryan Penno

—Darlene, via e-mail

A. Cellulitis, which is also referred to as phlegmon, is characterized by a severe, deep, suppurative (pus-forming) infection that spreads throughout the layers of tissue located underneath the skin. In some instances the infection can even extend to the skin surface, which results in pus-containing discharge draining from the skin surface. It is the combination of depth and severity of infection that can allow the disease to persist or reoccur. Because of this, cellulitis can be a frustrating disease to treat for both horse owners and veterinarians. In addition the need for prolonged treatment can become expensive.

The disease process starts with a wound that allows bacteria to breach the protective layers of the skin and spread to deeper tissues. Interestingly, the hind legs appear to be more commonly affected than the front legs. Other contributing causes to cellulitis include external parasites (e.g., mites), disease of the lymphatic vessels in the legs, and other unknown factors