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Cellulitis refers to bacterial infection and inflammation that affects tissues under the skin anywhere in the body. In horses, this severe condition typically occurs in the hindlimbs. It is characterized by a sudden onset with significant swelling and intense pain. [1]
If left untreated, the infection can spread to adjacent muscles and bones, causing severe and debilitating lameness. [2]
Resolving cellulitis in horses can be challenging and may necessitate surgical drainage. [2] Some horses experience recurrent flare-ups but implementing proper management practices can help reduce the likelihood of cellulitis flare-ups in your horse.
If you observe signs of cellulitis in your horse, seek immediate veterinary care. Cellulitis can rapidly spread up the leg and lead to sepsis, a severe and life-threatening condition. [3]
Cellulitis in Horses
Cellulitis is an inflammatory condition characterized by infection and acute inflammation of subcutaneous tissue.
It is commonly localized in the distal limbs, particularly the hindlimbs. It typically occurs due to pathogenic bacteria entering through skin wounds or breaks.
The infection leads to the infiltration of inflammatory cells, such as neutrophils and macrophages, which can lead to swelling (edema) and formation of abscesses.
Clinical Signs
Signs of cellulitis include severe swelling, pain, heat, and compromised limb function. Affected horses often exhibit a rapid onset of clinical signs, with severity ranging from mild to severe.
Swelling usually begins in one spot, quickly spreading to the rest of the limb. Other symptoms that can accompany swelling include: [1][4]
- Lameness
- Heat in the limb
- Sensitivity to touch
- Pitting (swelling that produces indentation when pressed)
- Fever (greater than 101.5oF or 38.6oC
- Depression
- Anorexia (loss of appetite)
- Tachycardia (fast heartbeat)
- Draining tracts on the skin’s surface and fluid discharge
Blood tests may show high white blood cell, neutrophil and fibrinogen counts, indicating infection and inflammation. Discharge may start to leak from the affected area within 24 to 48 hours after onset. If the infection goes untreated, it can potentially lead to systemic illness.[4][5]
Secondary Complications
Many affected horses develop supporting-limb laminitis in the contralateral leg (on the opposite side of the body). The limb with cellulitis is unable to bear weight, causing uneven and excessive weight bearing on the opposing limb. Unfortunately, affected horses that become laminitic often have a poor prognosis.
In addition to laminitis, several other secondary complications can develop in horses with cellulitis. These include: [4]
- Large areas of skin necrosis (dead tissue)
- Bacteremia (bacteria in the blood)
- Osteomyelitis (inflammation in the bones)
- Septic arthritis
- Endocarditis (inflammation of the heart)
If you observe signs of cellulitis, it is crucial to contact your veterinarian immediately. They can accurately diagnose the condition and initiate appropriate treatment.
Causes of Cellulitis in Horses
The precise underlying cause of cellulitis in horses remains unknown. Approximately 50% of cases develop without any apparent cause or specific trigger. [6]
Cellulitis is categorized into two types: primary and secondary. Primary cellulitis occurs without any identifiable underlying cause. While it is more commonly observed in Thoroughbred racehorses, any horse can develop primary cellulitis. [6]
Secondary cellulitis develops following trauma to the horse’s limb, resulting in an infection under the skin. Potential traumatic triggers for cellulitis include surgery, penetrating wounds, and joint injections. [1]
The bacterial organisms commonly associated with secondary cellulitis are Staphylococcus aureus and Streptococcus. These bacteria produce potent toxins that damage blood cells, skin and nerve cells in the affected area. [7]
These bacterial toxins also trigger a massive immune response involving several types of immune cells, including macrophages and white blood cells. The cytokines produced by these cells stimulate blood flow to the affected are