Any pus forming infection of the skin.


  • By depth of skin involvement.
  • By what organism is causing the infection.
  • By whether the infection is from a primary or secondary cause.

Clinical Signs

May observe any of the following:

Surface pyoderma
  • Patches of pruritic, red, irritated-looking skin with or without scabbing.
Superficial pyoderma
  • Inflammation (redness and swelling), moist eczematous lesions, papules or pustules.
  • Itching (pruritus), scratching, or chewing of affected area along with hair loss.
Deep pyoderma
  • Inflammation, ulcerative lesions with serosanguinous crusting and pus, and hair loss.
  • Itching may not be present at this stage; however, the rat may continue to chew, lick, or attempt to groom that area if in reach, particularly if there is discomfort or pain.

*Note: for additional information on recognizing various signs of pain or discomfort refer to: Signs of Pain In Rats.


An infection of the skin, pyoderma is seen as an inflammatory destructive disease that is frequently of unknown origin. Bacteria, primarily staphylococcal organisms, may be cultured although in many cases the bacterial cause may be elusive. This is due to the fact that often the bacteria that is cultured is normal resident flora of the skin.

Pyoderma can be divided into the following classifications: surface, superficial, and deep. It is also defined as being of a primary or secondary infection.

  • Surface pyodermas are called such because bacteria present on the skin, and involved in the infections, are confined to the surface of the skin. It may be seen as red, irritated looking, pruritic patches of skin. Scabs may present if the rat persists in scratching the affected areas.

  • Superficial pyoderma is sometimes seen as a cellulitis affecting the layer of skin at the level of the hair follicle. Normal skin flora or transient bacteria may colonize the area and adhere to the keratinocytes. Warm, moist areas are more susceptible as they have increased bacterial counts.

  • Deep pyodermas are just as the name suggests, extending well beneath the level of the hair follicle. Some diseases that can cause deep pyodermas are necrotizing fasciitis (flesh-eating disease), and neoplasms.
    Signs that may be seen are abscesses, tunneling of the skin, ulcerative (and necrotic) lesions, inflammation, lesions with serosanguinous crusting and pus, and hair loss. The area may also have an odor and be somewhat painful.

  • Primary pyoderma is often idiopathic in nature (occurring without any predisposing cause), usually in healthy animals, but may be a result of suppressed or compromised immune states. If bacterial infection is involved it is usually one organism as opposed to mixed or more than one organism such as in deep pyodermas.
    In primary or surface pyodermas the most frequent bacteria cultured is staphylococcus, a Gram-positive cocci bacterium. Staphylococcus is commonly found in the nasopharynx, lower GI tract, and as a natural resident on the fur and skin of rats.

  • Secondary pyoderma is primarily caused by conditions that involve bacterial infection below the epidermal layer of skin. Some conditions that can contribute to the presence of secondary pyoderma are ectoparasite infestations, fungal infections, atopic or contact type allergic responses, a weakened immune system as a result of poor nutrition or prolonged steroid use, cancer, or endocrine diseases like diabetes, hypothyroidism, or hypoadrenocorticism. The same is true of Superficial Pyoderma.

In rats with dermatitis, intense itching causes the rat to scratch and continually groom the area. An additional source of irritation may be caused by the barbering done by cagemates. This constant grooming and scratching can initiate lesions or aggravate them, and contribute to the source of staphylococcus in the wound. Other bacteria that may be a factor to a lesser degree is streptococcus (found to be a factor in necrotizing fasciitis/flesh-eating disease), which may contribute to abscess formation in deep pyodermas.

Excoriated skin lesions vary in size and are often suppurative having a serosanguinous type of weeping or drainage.
Although lesions are most likely to be seen in areas of the skin that have the most exposure to warmth and moisture, they can be found on other areas of the body as well. In these areas higher bacteria counts are likely to be seen on culture.

The length of the therapy will be based on successful elimination of whatever is causing the irritant. Pyodermas are difficult to resolve, and many tend to reoccur. Treatment tends to be long term.


Case Histories of Pyoderma (*note: graphic photos)

  • Fig. 1: Pyoderma involving the bacteria staphylococcus in female rat (Ruby)
  • Fig. 2: Pyoderma of unknown etiology, may be autoimmune
  • Fig. 3: Deep Pyoderma showing abscess with necrotizing fasciitis
  • Fig. 4: Stress related pyoderma in a 15-month-old rat (Selene)
  • Fig. 5: Superficial pyoderma in a 28-month-old male rat (Ritchie)


Any or all of the following may help to diagnose what what may be responsible for the occurring pyoderma.

Try to identify the type of lesions, if there is swelling, pus, ulceration or tunneling, and if loss of hair is present.

A hallmark of tissue invasion by staphylococcus aureus is a pus producing inflammation. It also has the ability to tunnel through and break down connective tissue.

Obtaining smears from intact pustules may help to determine bacteria involved.

Gram stain of affected tissue.

Skin scrapings for parasites, however, parasites may still be present even though the scrapings are negative.

Fungal culture for the presence of dermatophytes.

Skin tests for allergic or atopic dermatitis.

Work-up for metabolic or endocrine disease.

Try elimination diet provided in Food Allergies listed in the Rat Health Guide.


In all cases, as in dermatitis:

Clip toenails of rear feet to prevent increased trauma to lesions from scratching.

Consider separating from cagemates, for a short time, if barbering is an issue.

Surface Pyodermas

Application of topical therapy using skin cleansers, shampoos, creams, gels, or lotions can be used if appropriate.

Bathe affected area with a 1% Chlorhexidine, or 1% Chlorhexiderm solution, or Oxydex (contains Benzoyl Peroxide 2.5%) shampoo two times a week or as often as every other day depending on severity of condition. If the rat will tolerate, allow affected area to remain soapy for 10 to 15 minutes. Prevent rat from becoming chilled or licking and eating shampoo. Dry thoroughly. Ointment, if appropriate, should be applied sparingly.

Topical antibiotic creams for use with surface or superficial pyoderma:

  • Vet Aloe Vera cream
  • Privasan Antiseptic Ointment
    (A veterinary ointment containing: 1% chlorhexidine acetate in a hydrophilic ointment base and containing 10% stearyl alcohol)
  • Bacitracin and Polymixin B (for Gram-negative), applied sparingly, should not be used in the presence of purulent exudate.

The use of a systemic antimicrobial, although not generally needed with surface pyodermas, may be required if topical agents do not resolve the condition. See listing under Superficial Pyodermas.

Superficial Pyodermas

Use of both topical therapy and systemic antimicrobials as appropriate.

Recommended antimicrobials should be used for approximately 21 days or longer and continued for a week following resolution of lesions. Refer to the Rat Medication Guide for information on medications.

For treatment modalities of parasitic infestations see Ectoparasites on the Rat Health Guide Index page.

For treatment of fungal infections see Dermatophytosis on the Rat Health Guide Index page.

Deep Pyodermas

Systemic antimicrobials as noted above, as well as one of the aminoglycosides (e.g., amikacin or gentamicin) may be used.

Streptococcus spp. remains sensitive to Penicillin G, along with the addition of Clindamycin (Penicillin G dosage not yet listed in the Rat Medication Guide. Veterinarian to extrapolate dosage for rats), if this bacterium is believed to be involved.

Possible debridement may be required.

For surface, superficial, and deep pyoderma, corticosteroids such as: prednisone or prednisolone may be needed to reduce inflammation, swelling, or acute pruritus (itching) if present.

*Note: Antihistamines like diphenhydramine/Benadryl or chlorpheniramine/Chlor-Trimeton may be used if corticosteroids are not advised or need to be reduced.

Nursing Care

  • Use chlorhexiderm, or chlorhexidine at a concentration of not greater than 1%. Diluted solution should appear lighter than a robin’s egg blue.
  • Wash hands before care and after care to prevent further infection.
  • If rat persists in scratching affected area:
    • May apply a 1″ width self-stick vet wrap (e.g., Co-flex wrap) to the hind feet, like socks, to reduce the intensity of the scratching.
    • *Important Note: do not wrap so tightly as to impair circulation.
  • Continue treatment or follow up care until healing occurs, or if no improvement discuss change of medication treatment with veterinarian.
  • In the event antibiotics are given remember to include Bene-Bac, or yogurt with live active cultures, to prevent normal gut flora from being destroyed by the antibiotics.
  • Provide safe environment to help prevent traumatic injuries to skin or mucosal surfaces.
  • Look to eliminate offending causative agent.


  • Infection resolved
  • Lesions healed


  • Use of prepackaged processed litter, and the freezing of litter where bags have been breached prior to purchase, may be of help.
    *Please note: that any bags of litter/bedding that have been noted to have a row of holes in the top of the bag or any bag that has been breached during storage in pet stores and feed/tack warehouses, where contamination through contact from residing infested animals, may be a potential risk. Freezing the litter before using in cages may be a helpful preventative measure.
  • Thoroughly rinse cages when cleaning them with antiseptic solutions, prior to placing rats back in cages.
  • Refrain from serving foods known to cause allergic reactions such as peanuts/nuts.
  • Treat infestations of mites, lice, or fleas, early.
  • Assess skin on a daily basis and seek treatment advice from a veterinarian if signs and symptoms present.


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