Also Known As
Cellulitis is a bacterial infection of the soft connective tissues under the horse’s skin. Although cellulitis can occur anywhere on the body, in horses the infection commonly occurs in the hind legs.
Cellulitis typically starts with sudden swelling that is warm and painful to the touch. Frequently, horses developing cellulitis will not eat becuase of fever and discomfort and will be depressed. Some will tremble, breathe rapidly and sweat.
Unlike stocking up or “filling” of both hind legs sometimes seen in horses that are kept in stalls, cellulitis usually produces swelling in only one leg, almost always in a hind limb. If left untreated, cellulitis can be a life-threatening condition in horses.
- Prominent swelling on horse’s leg
- Refusal to place weight on limb
- Pitting edema (imprints when area is touched)
- Painful to touch
- Off feed
Cellulitis is caused by infection and inflammation of subcutaneous tissues under the horse’s skin. Poor hygiene, bacterial population on the skin, decreased blood/lymphatic circulation and breaks in the skin are all thought to play a role in the development of celllutitis.
A small scratch or wound can lead to the development of the condition, alhough in some cases no wound can be found. Cases of cellulitis often follow an insult to the affected area such as surgery, trauma, joint injections, or a wound. It is not known why some wounds don’t produce cellulitis, while other injuries cause a leg to swell up.
The most common bacteria to be isolated from these cases are Staphylococcus spp. which normally inhabits the horse’s skin. These bacteria then enter the deeper tissues and lead to infection through a break in the skin barrier.
Edema in these tissues then forms when the bacteria and the toxins they release create an inflammatory response. This leads to blood vessels and lymph vessels becoming leaky and tissue building up in the subcutaneous tissue.
Some horses also develop chronic lymphangitis, a chronic form of cellulitis that occurs in horses who have impaired lymphatic drainage. Lymphangitis or impairment of lymphatic flow can set the affected limb up for infection by allowing fluid to pool rather than drawing it out again as normal.
Veterinarians recommend that owners take preventive measures, to prevent development of cellulitis including keeping horse limbs clean and using disinfectant soaps on all abrasions and cuts. Some veterinarians prescribe daily aspirin therapy to prevent cellulitis, but there is no scientific evidence that this is effective.
Keeping horses in sanitary conditions with regular mucking of stalls and taking care during wet weather to protect horses from standing in mud and manure is important in preventing infection.
Getting rid of excess fluid is a crucial part of treatment once cellulitis is diagnosed. Getting the horse moving, such as by hand-walking several times a day, helps to achieve this, but a veterinarian may recommend other options that can help draw the accumulated fluid out of the limb.
Hydrotherapy with cold hosing, bandaging, sweat wraps in addition to hand-walking or lunging are crucial components of treatment and are used in combination to help reduce the swelling of the limb.
Ultrasound can be very useful at the subcutaneous tissue level and in highlighting the presence of edema, seen as fluid accumulation within the tissue layers.
Direct treatment of cellulitis focuses on eliminating the infection from affected tissues and supportive care to decrease the limb swelling.
Broad spectrum antibiotics are commonly used to help clear the infection. NSAIDs can also be used to help control pain and inflammation.
Intravenous dimethyl sulfoxide (DMSO) can be used as an anti-inflammatory. Corticosteroids (e.g., dexamethasone) and diuretics (which increase urine production) might also help draw out the swelling
Treatment can be quite frustrating as many of these cases take a while to resolve and full resolution is not always achieved.
It is important to get your veterinarian involved when a case of cellulitis is suspected as prompt diagnosis and treatment are crucial to successful recovery.
Ruling out other causes of severe lameness and limb swelling including joint infections and fractures are an important first step in determining if cellulitis is present. Supporting diagnostics are then used to confirm and assess the extent of the condition.
Some horses undergo very severe and deep infections that cannot be corrected with medical management alone and surgical debridement or drainage is necessary.
In other cases, thrombosis of vessels can occur which leads to necrosis of tissue and skin sloughing wounds. These wounds can involve important underlying structures and may require a long and expensive period of intensive wound care and bandaging to resolve.
In addition, laminitis can occur in the affected limb due to damage to the coronary band or can develop in the contralateral limb due to the extra stress placed upon that limb.
Although survival rates are quite high and treatment is often successful, prognosis for a full recovery is not guaranteed.
Some horses may have recurrence of the infection or suffer from lameness when returning to normal work loads after the initial episode.
Chronic cases will often lead to a permanently thicker leg due to the presence of scar tissue. This can permanently affect the horses’ ability to normally drain the lymphatic system. Horses that are prone to recurring episodes are often maintained on strict exercise programs and extra care is taken to ensure proper hygiene and prevent exposure to infections.