Abscess is defined as: a circumscribed collection of puss frequently associated with swelling and other signs of inflammation which oftens leads to a cavity of liquefactive necrosis within solid tissue. Most folks think of an abscess as a localized pocket of infection but this is not always true. Puss, or perhaps nicer sounding purulence, is a fluid that is a product of inflammation. It consists of a liquid containing white blood cells (leukocytes) and the debris of dead cells and tissue elements liquefied by the proteolytic and histolytic enzymes that are released by the white blood cells. While infection often leads to puss formation, there are also sterile abscesses which often are created by the body's attempt to dissolve dead tissue. The body makes puss to fight infection as well as to remove damage tissues.

Abscesses most frequently result from a penetrating injury that does not drain well. However there are some systemic infections that manifest themselves as abscesses. The treatment of a focal abscess of any origin is the same while internal and disseminated abscesses depends on the organism present. This article deals with the diagnosis of abscesses and internal abscesses, treatment, and links to specific diseases that cause abscesses. For hoof abscesses see: Hoof Abscesses.

Most abscesses are a straightforward diagnosis. History of a penetrating injury or onset of disease that is associated with abscess formation that after several days develop increased swelling, heat, and pain is almost assuredly pocketed up infection. Fever will generally be present but may be reduced by the use of NSAID's. Rapid onset of severe lameness and swelling in the foot and pastern area is probably a solar abscess...more.

It is easy to confuse blunt trauma or mild vaccine reactions with the early stages of an abscess. There are some characteristic differences:

• Timing of the onset of problems can be an important clue to an injury. If heat, swelling, and pain worsens several days after the initial insult, this is probably infection.
• Progress can help differentiate noninfectious and infectious inflammation. Inflammation from trauma or vaccines generally develops over two to 12 hours but then plateaus and then begins to resolve. Infection tends to be progressive over several or many days.
• Response to phenylbutazone or other NSAID can be helpful: noninfectious inflammation is very responsive to these drugs while infection is not. It may improve slightly but will continue to be unusually hot and painful.
• Note well: surprisingly response to antibiotics is a poor indicator of bacterial disease. The reason is that noninfectious causes of inflammation is almost always self limiting and will begin to resolve with time, so it always appears the antibiotic is working. Lack or response to antibiotics does not always mean it is not a bacterial infection: resistance, inadequate dosage or frequency, or poor drainage will all make antibiotics less effective.

Internal Abscesses

Internal abscesses can form inside the body cavities and therefore are not directly observable. Diagnosis can be difficult as the symptoms are one of general malaise and poor doing. You might see: chronic or recurrent fever, colic, jaundice, weight loss, and generalized poor doing. Further support of the diagnosis can be made with blood work particularly: CBD and fibrinogen. Fibrinogen is particularly important because some chronic infections and abscesses can have normal white blood cell counts and differentials. However, fibrinogen is a very sensitive indicator of ongoing inflammation. It is important to note that acute infection, cancer, trauma and any cause of inflammation will all elevate the fibrinogen levels so it must be interpreted in light of history and other findings. Another warning is that it requires special handling with the technique dependent on the way the lab runs the test. The sample should be kept cool and the sample ran within 12 hours. Normal values run in the 100 to 400 mg/dL range and will change rapidly in response to changing levels of inflammation.

Some of the common infectious abscessing diseases have specific blood tests (serology) for them. Most common are:

• Corynebacterium pseudotuberculosis also called Pigeon Fever and Dryland Strangles
• Streptococcus equi sub specie: equi known as Bastard Strangles
• Rhodococcus equi the causative agent of Foal Pneumonia

History of exposure to or the disease being endemic in the areas will help with diagnosing these problems. Other ways internal abscesses can be diagnosed and further localized is with rectal palpation, ultrasound, radiography, and peritoneal tap and fluid cytology.