—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.
Although the initial cause of cellulitis cannot always be identified, certain environmental conditions—including prolonged exposure to deep mud or sand (both can cause drying and irritation of the skin, which allows bacteria to break through its protective barrier)—can promote cellulitis development.
Common clinical signs associated with cellulitis include painful swelling, heat, and lameness of the affected leg.
Identifying and treating the cause of the cellulitis is ideal, but is not always possible. You should discuss specific treatment of horses with your veterinarian, as different causes can require specific treatments (e.g., the use of antiparasitic drugs in horses with mite infestation). However, antibiotics and non-steroidal anti-inflammatory drugs (such as phenylbutazone or flunixin meglumine) are often warranted to treat the bacterial infection and the associated inflammation.
In addition to these medical treatments, I typically advise my clients to keep the affected leg clean, and if long hair is present, to clip it. In some cases, cold-hosing the leg and applying a pressure wrap are beneficial. Only apply a pressure wrap if your veterinarian has provided you with training on how to do so properly, as further injury could occur if a wrap is applied improperly.
Preventative measures include:
- Maintaining a regular exercise program, as long as the horse is fit to do so. This helps improve fluid drainage through the lymphatic system from the legs.
- Keeping the legs clean and dry.
- Avoiding turning horses out in areas with standing water, mud, and sand, if possible.
- Observing your horse closely and communicating with your veterinarian for early detection of reoccurrence and prompt initiation of treatment.
As previously discussed, the disease outcome and the potential for disease reoccurrence depends on the severity and degree of damage from previous episodes. Generally, most cases resolve uneventfully with minimal risk of reoccurrence. However, if enough scar tissue develops to decrease the body’s natural ability to drain fluid from the area, the affected leg might remain swollen to varying degrees. Similarly if enough damage has occurred to weaken the skin and the protective defenses of the underlying tissues to infections, reoccurrence is likely. This means that continued monitoring of your horse’s leg and good communication with your veterinarian is especially important to minimize the risk of permanent damage.