Pyoderma in Cats (Bacterial Skin Infection, Pus in the Skin)

Overview of Bacterial Skin Infection in Cats

Pyoderma is a bacterial infection of the skin. Pyoderma can be divided into surface pyodermas (infection on the skin surface), superficial pyoderma (infection within the skin) or deep pyoderma (infection under the skin).

The health impact from pyoderma can range from mild with superficial pyoderma to severe with deep pyoderma. Superficial and surface pyodermas can cause intense itching leading to discomfort. The underlying cause of the pyoderma may also have a negative health impact on the cat, depending on the disease.

Pyoderma can be caused by underlying allergies to food, fleas or other things in the environment, and/or immune-medicated diseases.

The most common bacteria causing pyoderma is Stapylococcus pseudointermedius.

Deep bacterial infections are more common in outdoor cats. Cats are predisposed to pyoderma in warm humid environments.

What to Watch For with Pyoderma

Any of these should trigger a visit to your veterinarian:

• Red, itchy and painful skin lesions
• Pustules (pimples)
• Draining sores
• Hair loss

Diagnosis of Feline Pyoderma

Diagnostic tests may include:

• A detailed medical history. Expect to be asked about how long the lesions have been present, what they looked like initially, and whether itching preceded the lesions or appeared after the lesions.
• A complete exam of all body systems with particular attention paid to the type and location of lesions present in the skin.
• Cytology. A pustule may be opened and the contents examined under a microscope. With a pyoderma, bacteria and neutrophils (a type of white blood cell) are usually seen. Neutrophils without bacteria may suggest another disease.
• Culture. Deep pyodermas are typically cultured to identify the exact bacteria that are present and to help select the best medication. Superficial pyoderma lesions are rarely cultured since they almost always grow the same bacteria (Staphylococcus intermedius).
• Other tests, such as skin scrapes, allergy tests, complete blood count or blood chemistry analysis, to determine the underlying cause of the pyoderma, especially if the pyoderma recurs after treatment.

Treatment for Feline Pyoderma

Treatment may include:

• Antibiotics to help kill the bacteria infection. The most commonly used antibiotics include cephalexin, Clavulanic acid-amoxicillin (Clavamox), Clindamycin, and Cefovecin injectable (Convenia).
• Antibacterial shampoos and creams containing benzoyl peroxide, ethyl alcohol or chlorhexidine.
• Treatment to prevent underlying itchy skin diseases or diseases that suppress the immune system for long-term success.

Home Care and Prevention for Pyoderma

Give all medications as instructed. Even if lesions clear up early, antibiotics should be given until all medications are finished. Observe your cat for draining lesions.

Some causes of pyoderma are not preventable, but the presence of fleas can worsen pyoderma. The best prevention is to follow a complete flea control program as recommended by your veterinarian. In addition, keep your cat clean and brushed free of mats.

In-depth Information on Feline Bacterial Skin Infections

Surface Pyoderma

• A hot spot (pyotraumatic dermatitis) is a surface pyoderma that is caused by self-trauma due to some itchy problem, often an allergy. It has the appearance of a moist, red lesion with acute loss of hair and is intensely itchy.
• Skin fold pyoderma occurs in folds of skin that are moist and difficult for the animal to keep clean. Examples are: facial fold, tail fold, vulvar fold and lip fold pyoderma.

Superficial Pyoderma

• Superficial pyoderma is infection within the skin. The bacterium that is nearly always incriminated in this infection is Staphylococcus intermedius. This form of pyoderma is the most common kind and affected animals have pustules that may rupture leaving a ring of scale that is called an epidermal collarette.
• Pruritus (itching) leads to self-trauma that causes damage to the skin and breakdown of natural defense mechanisms allowing bacteria to penetrate into the epidermis causing pyoderma. Examples are allergy and infestation of parasite like mites or lice.
• A suppressed immune system may allow bacteria to establish an infection within the skin. Examples are: hormonal diseases, like Cushing’s disease or hypothyroidism, some infectious diseases, cancer or any disease that suppresses the immune system. Excessive use of corticosteroids like prednisolone can suppress the immune system.
• There are some cases of pyoderma that recur after treatment, yet an underlying cause can never be found. This is called idiopathic pyoderma or primary pyoderma.
• Superficial pyoderma must be differentiated from other diseases that present with pustules such as autoimmune skin diseases and certain fungal skin diseases.

Deep Pyoderma

• Deep pyoderma is rare in cats but is much more severe than the more common forms. Cats with deep pyoderma have severe bacterial skin infections with open, draining sores and fever. These animals are very sick, are often not eating and are very depressed.

Diagnosis In-depth for Skin Infection in Cats

Your veterinarian will take a thorough medical history and examine all body systems. Other medical tests will be necessary to establish the diagnosis.

• Microscopic examination. Your veterinarian may open a pustule and apply the material within the pustule to a microscope slide. The slide is then stained and viewed under a microscope. The presence of pyoderma will reveal bacteria with white blood cells, especially neutrophils.
• Culture and antibiotic sensitivity. In cases of deep pyoderma lesions, this test must be done to identify the bacteria responsible and to select the most appropriate antibiotic. Cultures of superficial pyoderma pustules are rarely done, since they nearly always grow Staphylococcus intermedius.
• Visualization. Your veterinarian can usually diagnose surface pyoderma by visualization of the lesion. Hot spots have a characteristic appearance of a moist, red skin lesion with sudden hair loss. Skin fold pyoderma is a red, moist lesion associated with a skin fold. Hot spots are triggered by an itchy skin problem. Thus, diagnostics to determine the itchy underlying cause may be necessary, especially with recurrent hot spots. Often, flea allergy is the culprit.
• Superficial pyoderma may cause a cat to be itchy. This can cause confusion in the diagnostic process since itching may lead to pyoderma. The veterinarian may ask if your cat’s lesions preceded the itching or if the itching preceded the lesions. If the itching came first, then a pruritic underlying cause is suspected. If the lesions appeared first, then immune suppression may be the cause.

If itching is suspected, the following tests may be done to determine the source of the problem:

• Examination of the skin and hair with a flea comb for fleas and lice
• A skin scraping to look for mites and other microscopic parasites
• Fungal cultures to rule out ringworm fungus (dermatophytes). These skin fungi may cause itching and lead to a secondary pyoderma.
• Allergy testing or a food trial to rule out food allergy in chronic cases of pyoderma

In cases where superficial pyoderma is suspected to be caused by immune suppression and in all cases of deep pyoderma, tests are needed to look for the cause of the immune deficiency. Examples include:

• Tests for Cushing’s disease (hyperadrenocorticism), a disease where the adrenal glands make too much of a hormone called cortisol. One effect of the excessive cortisol can be immune suppression.

Treatment In-depth for Skin Infection in Cats

Treatment for pyoderma involves treatment of the underlying cause and elimination of the resulting infection.

• Surface pyodermas such as hot spots are best treated by clipping of the wound and cleaning with an agent that kills the surface bacteria. Antibiotics often are not needed since the bacteria is on the skin surface and not within or beneath the skin. The source of the itching that led to the hot spot must be identified and treated (e. g. fleas). Skin fold pyoderma is treated by clipping hair from the fold and cleaning with an agent to kill the bacteria. Recurrence of the problem may require surgical removal of the fold.
• Superficial pyoderma is treated with antibiotics that are effective against Staph. intermedius. This type of bacteria does not respond to some of the more common antibiotics such as penicillin, amoxicillin, ampicillin, or tetracycline. Thus, more potent antibiotics must be used. Three weeks of treatment is usually required for effective therapy.
• Superficial pyoderma often responds to a appropriate antibiotic when it is used long enough. However, unless the underlying cause is also addressed, the infection often recurs soon after treatment is stopped. Diagnosis and treatment of the underlying cause is essential to long-term success. The most commonly used antibiotics include cephalexin, Clavulanic acid-amoxicillin (Clavamox), Clindamycin, and Cefovecin injectable (Convenia).. Antibiotics are often given for 3 – 4 weeks or at least 1 to 2 weeks after all symptoms are resolved. Other antibiotics used include cefpodoxine, cefadroxil, azithromycin, erythromycin, doxycycline, oxacillin, lincomycin, tylocin, difloxacin, enrofloxacin, marbofloxacin, orbifloxacin, and trimethoprim sulfa.
• In cases where the underlying cause can not be determined, antibacterial shampoos may be helpful in preventing recurrence. Examples of antibacterial shampoos are those that contain benzoyl peroxide, ethyl lactate, povidone-iodine or chlorhexidine. It is important to give the shampoo appropriate contact time with the skin which is generally 10 to 16 minutes. Hair should be trimmed or clipped off affected areas.
• Creams and lotions that contain the above chemicals may be useful for treatment of small lesions. Most cases of pyoderma affect a large area of the body, making this approach impractical.
• Injections of immune stimulants or immune modulators such as staphage lysate may be helpful. These are usually reserved for cases that do not respond to more traditional treatment.
• Deep pyoderma must be aggressively treated with antibiotics selected from culture and bacterial sensitivity. The bacteria that are isolated from the lesions are incubated with several antibiotics in culture media to see which ones can kill those particular bacteria. Antibiotics must be given until a few weeks after all lesions are resolved. Often, 6-12 weeks of treatment is necessary.
• The immune problem that is underlying the deep pyoderma must be determined and treated to achieve success.
• Whirlpool baths may be helpful, as an aid in treating deep pyoderma is your vet has this available.

Home Care for Skin Infection in Cats

Optimal treatment for your cat requires a combination of home and professional veterinary care. Follow-up can be critical, especially if your cat does not improve rapidly.

Most cases of surface and superficial pyoderma respond well to the therapy outlined above and therefore require little follow–up, unless the case is recurrent or never resolves. Deep pyoderma requires regular recheck exams to monitor for progress.

Be sure to administer all prescribed medication as directed, and alert your veterinarian if you are experiencing problems treating your cat. Antibiotics can have side effects that may require the antibiotic to be stopped temporarily or to be changed to a different medication. The most common side effects are related to irritation of the stomach and intestines. Thus, vomiting or diarrhea may occur. More severe drug reactions may occur but are uncommon. Be sure to let your veterinarian know if any new symptoms occur with antibiotic therapy.

Prognosis for Pyoderma in Cats

The prognosis for pyoderma is good with appropriate therapy. Identification and treatment of the underlying factors causing the pyoderma is essential.