Page 38 - New Mexico Horse Breeder Spring 2018

Cellulitis In Horses
Cellulitis is a diffuse inflammation, generally associated with bacterial infection of the subcutaneous tissue. “In horses, cellulitis
usually refers to swelling of a limb and typically involves only one limb, most often a hind limb,” says Dr. Margaret Mudge, Associate Professor of Equine Surgery and Emergency and Critical Care, at Ohio State University.
“The term cellulitis is very general, referring to infection under the skin and sometimes involving the skin. It can occur in many areas of the
body, often related to injury such as a puncture
or laceration, or sometimes a surgery site. But when we talk about cellulitis in horses, we tend to think of the hind limb. Regarding causes, we differentiate between primary cellulitis (meaning there is no obvious wound or known trauma/ disruption to the skin) or secondary cellulitis. In the latter situation, there is usually a wound or joint infection or a surgical site that has become infected.”
Primary Cellulitis
Cases of primary cellulitis are often a mystery regarding the cause. “In nearly half the cases
we see, we never really know what started the infection. There are two very good retrospective studies that were published in the past 12 years, and their results are very similar to what we’ve seen in our hospital. About half the cases we see are a primary cellulitis; there is no known trauma or obvious wound,” says Mudge.
The theory is that there might have been blunt trauma or soft tissue bruising under the skin, allowing bacteria to settle there in the damaged
Bacteria may be introduced through blunt force trauma or soft tissue bruising under the skin.
by Heather Smith Thomas
tissue. “We don’t know if the bacteria were already in the horse’s body or if they were introduced through the skin. There are probably some that were in and around the skin, potentially systemic. Some are mixed bacterial infections, but the bacteria implicated most often are Staphylococcus aureus and Streptococcus. These are common bacteria that are often found in the skin,” she says.
“These bacteria may get dragged in through tiny punctures that we can’t see and may get through the skin if there is enough damage to the underlying tissues that the barrier is compromised and they are able to gain entry. Some people think this may be related to a syndrome seen in racing greyhounds; there may be some dermatitis or compromised skin that has lost some of its barrier function and is allowing bacteria to gain entry,” she says.
“Thoroughbreds seem to have more cases
of cellulitis than other horse breed, but we are
not sure why. A person could theorize about Thoroughbreds being a sensitive breed, but I haven’t seen any reports on whether this is actually a breed-related factor or whether it has to do
with racing versus other careers and management practices that may for some reason put them at risk,” says Mudge.
Symptoms
Most often the swelling appears suddenly. “Usually there is also a lot of pain, so one of the first signs will be lameness. The leg is usually diffusely enlarged, sometimes all the way from the foot up to the stifle or beyond. The typical case
is generally swollen from at least the foot to the hock and the leg is usually very warm and painful to the touch. If you press the leg, this triggers a pain response,” says Mudge.
“Depending on how severely swollen it is, the leg may be oozing serum, weeping through the skin. Often it’s just one leg that’s swollen, and
this is one way to differentiate it from stocking up (simple edema). Some horses that have had previous bouts of cellulitis may always have a little bit of a stocked up appearance in that leg. These horses may have recurrence of cellulitis, but it may come on more insidiously than suddenly, compared to acute cases,” she says.
The term cellulitis is very general, referring to infection under the skin and sometimes involving the skin. It can occur in many areas of the body, often related to injury such as
a puncture or laceration, or a surgery site. When we talk about cellulitis in horses, we tend to think of the hind limb.
Depending on how severely swollen it is, the leg may be oozing serum, weeping through the skin.
36 New Mexico Horse Breeder