Abscesses are a common problem in cats. It is hard to say why cats develop abscesses more frequently than other domestic species but there are several plausible reasons. A bite from a cat wound is more likely to become infected than a bite from most other species due to the bacterial residents of cat mouths. Since cats bite each other fairly frequently this is certainly one reason for the high number of abscesses. This situation is exacerbated by the tendency for cat bite or scratch wounds to have small entry wounds but to cause damage subcutaneously which becomes infected after the small skin wound is already healed. Cats also are prone to immunosuppressive viral illnesses such as feline immunodeficiency virus and feline leukemia virus which makes infected cats more likely to suffer an abscess after a wound.
Most abscesses start out as cellulitis, which is infection of the tissues under the skin. In some cases it is possible to prevent abscess formation by early detection of the presence of cellulitis. Signs of early infection may include lameness, localized pain, lethargy or reluctance to eat. If your cat exhibits any of these signs and your vet can determine that cellulitis is present early administration of an appropriate antibiotic may prevent abscess formation.
After a brief period of cellulitis, an abscess forms. The cat's body attempts to fight the bacterial infection by forming a capsule around it and flooding the capsule with a large number of white blood cells. This collection of white blood cells and bacteria is commonly referred to as pus. I f the cat is really successful at walling off the infection there may be a small abscess. If the cat is less successful at dealing with the initial infection the abscess may be very large. In this case the abscess may cause the skin over the abscess to die. The skin usually turns black and becomes very hard to the touch after it dies. It will fall off eventually if left in place but it is better to remove the dead skin to allow healing to occur faster and to ensure that the abscess can be properly treated. Abscesses that occur around the base of the tail are very prone to causing skin sloughing. Early aggressive treatment is best when there is pain or swelling around the base of the tail.
Abscesses are generally treated by opening them up to allow them to be adequately cleansed with an antiseptic. Abscesses can be very painful. If a cat will not allow an abscess to be opened due to the pain it may be necessary to use an anesthetic agent so that the abscess can be properly treated. If there is dead skin over the abscess is should be removed as well. It surprises many clients that this can often be done without an anesthetic agent, since the dead skin has little or no feeling. The live edges still have nerve endings and many cats do object, though. After the abscess is cleaned most vets will prescribe antibiotics. There is a wide variation in the way antibiotics are used by veterinarians in the case of abscesses. In general it is possible to treat most abscesses with ampicillin or amoxicillin since the majority of abscesses are caused by bacteria that are susceptible to these antibiotics. Once started the antibiotics should be used for at least three days and it is important to use appropriate dosages. It is not usually necessary to use antibiotics longer than seven days and it is often appropriate to use them for three to five days only.
Some abscesses do not respond to standard therapy. Almost every veterinarian who treats cats has run across an abscess that seems impossible to cure. If this happens there are a number of possible causes. It is usually a good idea to culture the abscess site in this case. If the bacteria involved can be grown and identified it helps a great deal. If the bacteria can be grown on a culture plate it is possible to try to kill it with a number of antibiotics and pick one that works -- at least on the culture plate. If it appears that a new antibiotic is necessary that may be enough to cure the problem. Sometimes that isn't enough to cure the abscess, though.
When abscesses do not respond to treatment with standard treatment and after identification of bacteria that can be cultured from the wound it is time to look for underlying causes or complicating causes. There are several things that cause abscesses to be difficult to treat. Feline leukemia virus infection or feline immunodeficiency virus infection can cause the immune system to fail to help clear up the abscess. Despite the "wonder drug" label, antibiotics often need the help of the body's natural defenses to cause a cure. Sometimes the infection is caused by an unusual organism that does not respond to the same antibiotics used for the most common bacteria found in bite wounds. Mycoplasma infections will respond to tetracycline antibiotics in most cases. Nocardiosis infections respond to sulfa/trimethoprim antibiotics used at two to three times the usually recommended dosages. Actinomyces infections may respond to very high dosages of penicillin. A newly recognized variety of bacteria, l-form bacteria, usually respond to tetracycline antibiotics. This form of infection may not be known to your veterinarian. It usually appears as an infection affecting multiple joints with several abscesses or draining tracts that does not respond to conventional therapy. The l-form bacteria can not be cultured in the same way other bacteria are so they are difficult to diagnose. Response to tetracycline may be the best "diagnostic" test available to the general practitioner since confirmation of infection may require examination of abscess contents with an electron microscope.
Abscesses vary in severity from a relatively minor problem that the cat's immune system will handle on its own to complicated, life threatening infections. It is best to treat them early, establishing proper drainage if at all possible, cleansing with an antiseptic and in most cases appropriate antibiotic therapy. Some abscesses are not going to respond to routine treatment methods and will require multiple visits and become very frustrating, both for you and your vet. If an abscess is not responding to treatment it is vitally important that you alert your vet and that you continue to work with your vet to resolve the problem. You may have to push a little for diagnostic testing or use of tetracycline based antibiotics to rule out l-form bacteria and Mycoplasma infections in chronic abscess situations since there is a tendency among veterinarians to continue to use broad-spectrum antibiotics in the face of resistant abscesses rather than switching to medications with a narrower spectrum of action such as the tetracyclines. It is probably not a good idea to use tetracyclines routinely since they do not work as well against the most common forms of infection as other antibiotics and because their mechanism of action makes them harder to combine with other antibiotic therapy to achieve a broader spectrum of action.
Neutering male cats greatly reduces roaming behavior and fighting associated with seeking mates. This also reduces the incidence of abscesses in male cats. It may be best to avoid the whole issue of abscesses by taking this preventative measure!
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