Treating Abscesses in Horses
Abscesses are common problems in horses. They can range from easy-to-identify-and-treat foot abscesses to abscesses that are very difficult to diagnose and even harder to treat (e.g. brain abscesses, abdominal abscesses).
An abscess is an accumulation of pus. Pus is basically dead bacteria, partly broken-down cellular debris, and white blood cells. Sometimes there can be a thick capsule of tough, fibrous tissue surrounding an abscess, particularly if it has been there for a long time (see picture left). Most abscesses occur as the result of a local infection that the body was able to contain (at least partly), but could not eliminate altogether, and that didn't "drain" naturally to an open space (e.g. outside the body). Over time, some abscesses may continue to grow and become quite large, which can cause many different problems depending on where the abscess is. "Sterile" abscesses can also occur, but are much less common - these lesions are not associated with a bacterial infection, but may occur following a severe trauma or in association with certain tumours.
Because abscesses are usually caused by an infection, it's logical for people to think about using antibiotics to treat them. However, antibiotics are not very effective at treating abscesses because:
- Abscesses have very little blood supply. A good blood supply is needed to deliver antibiotics to an infected site.
- Many antibiotics do not penetrate into abscesses well because of the tough capsule and the type of fluid within the abscess. Some do a better job than others, but none are great.
- Even if an antibiotic is able to penetrate an abscess, it may be only minimally effective due to the amount of pus and bacteria that are usually present.
So, if we can't use antibiotics effectively, what do we do? The most effective treatment for any abscess is incision and drainage. This involves lancing the abscess to remove as much of the infected pus as possible. It also allows for local treatment such as flushing with antiseptics. Antibiotics should only be used when there is no way to drain (lance) an abscess, such as with lung abscesses.
If an abscess can be lanced, it should be, with very few exceptions. That may involve paring out a foot abscess, lancing a strangles-infected lymph node, or opening a large abscess from a wound. Lancing of abscesses should always be done by a veterinarian. While it may be tempting to "pop" an obvious abscess yourself, there may be important blood vessels or nerves in the area that need to be avoided. The abscess that you see may be only one part of the problem, and other diagnostic tests or treatments may be needed. A veterinarian can pick the best part of the abscess to lance, to ensure the best possible drainage, and a veterinarian can provide proper sedation and local anesthesia for the horse during the procedure. An ill-placed stab at an abscess can make things a lot worse.
Photo: A large abdominal abscess from a horse that was drained and opened to show the very thick outer fibrous capsule, and many thinner, internal loculi. (M. Anderson)
