XL Equine vet Dr. Aoife Byrne DrMedVet MRCVS explains about a case of cellulitis and how to prevent it.

Dr. Aoife Byrne is a veterinary surgeon based at Chapelfield Vets in Norfolk.

“The leg was normal yesterday and now it’s the size of a tree trunk!” This is a commonly heard complaint from worried owners at this time of year. Continuously wet or muddy legs with or without mud fever are the perfect environment to incubate a case of cellulitis. It is a diffuse (widespread) inflammation/infection, generally associated with bacterial infection of the skin and the soft tissue directly underneath the skin. In horses, it generally involves only one limb.

The disease can be divided into cases with a known cause, or secondary cellulitis, and those with no obvious underlying cause, named primary cellulitis. The main causes of secondary cellulitis include infections that occur following surgery, joint injections, wounds, or blunt trauma.

Primary cellulitis is thought to arise from a break in the skin that could be as small as the tiny puncture wound created by an insect or mite bite. In most of the cases I see, the break isn’t obvious, and it appears as though the limb simply swelled up for no reason. In most cases it’s assumed that the infection is caused by staphylococcal organisms, since staph is the chief inhabitant of equine skin surfaces. In many instances, we can’t confirm the actual pathogen involved, but certain environmental condition 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.

Some horses seem to be more prone to develop it than others with the thinner skinned/less hairier breeds the ones I see most often with the condition. Today’s patient Fin was a retired Thoroughbred racehorse who had suffered with previous bouts. His owner was well aware of the typical signs like heat, swelling and pain in a limb, sometimes centred around a given area such as a hock or pastern, and sometimes a more diffuse swelling extending up and down much of the limb. The swelling itself is usually hot, painful, and pits when firm pressure is applied. The horse is lame & sometimes unable to bear weight on the affected limb (more commonly a hind limb than a front limb). The lameness develops acutely, and may precede the marked swelling that follows within a few hours. Owners often suspect that the horse has a fracture due to the severity of the lameness (i.e. horses can be toe touching to non-weight bearing lame). The horse may develop a fever (temperature > 101.5°F or 38.6°C).

Fin’s owner had started with some physical therapy measures to alleviate the symptoms which are very important to help maintain circulation during and after the infection. The swelling that occurs due to oedema build-up, is not only painful in the initial stages, but is often hard to get rid of even once the infection has resolved and this can lead to continued lameness issues. Principles of therapy aimed at minimizing inflammation, oedema accumulation, and swelling include compression and cryotherapy. Compression (by bandaging the limb) has been shown to be effective in stimulating tissue healing, minimizing oedema, and increasing blood flow. Cryotherapy (cold hosing or ice boots) reduces the inflammatory response in the tissue, reduces the metabolic demand of the tissue, and provides a short-term analgesic effect. Also hand walking (when the horse is comfortable enough to) and massage will assist circulation and encourage fluid drainage.

Unfortunately, despite Fin’s owner’s best efforts, the heat and swelling didn’t dissipate sufficiently, so serum started to seep through his skin. This combined with an elevated body temperature and the fact he started to go off his food meant his owner knew it was time to call the vet, as antibiotics and anti-inflammatories would be needed. After careful examination of the leg a small self inflicted wound was found – the probable entry point for the infection. Fin was prescribed five days of oral antibiotics and Bute. After two days his owner rang to say the leg had returned to normal, but I advised it was very important that she finish the full course of treatment.

I also advised them of these measures to prevent further bouts over the winter months:

* Maintain a regular exercise program or plenty of daily turnout as long as the horse is fit to do so, as this helps improve fluid drainage through the lymphatic system from the legs.

* Keep your horses legs clean and dry as loss of skin integrity is an important risk factor for cellulitis.

* Bathing equipment (sponges) may act as a carrier for the causative bacteria, or the act of bathing may predispose the skin to drying and chapping. Therefore hygienic handling of bathing equipment and careful drying of limbs after bathing is highly recommended.

* Avoid using harsh disinfectants like chlorhexidine.

* Don’t turn-out horses in areas with standing water, mud, and sand, if possible.

* Observe your horse closely and communicate with your vet for early detection of reoccurrence and prompt initiation of treatment.

* Use protective leg boots if your horse is prone to self-trauma while turned out or during exercise.