Definition

Dermatitis, a term also used when referring to eczema, means a superficial inflammation of the upper layers of skin.

Clinical Signs

Any of the following signs may be present depending upon the underlying cause, type, or severity of the dermatitis:

• Pruritus (itching), scratching, inflammation (redness and swelling).
• Lesions on neck, lateral shoulders, or rib cage.
• Miliary lesions (small bumps like small grains of millet).
• Yellowish or reddish bumps on tail.
• Crusting, scaling, and oozing.
• Patchy alopecia (partial hair loss) that may or may not be present depending upon severity of symptoms.

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

Etiology

There are many causes (some unknown) and types of dermatitis. Some of the more common types are contact dermatitis, atopic dermatitis, seborrheic dermatitis, and ulcerative dermatitis.

Contact dermatitis

A form of eczema that is divided into two classifications: primary irritant contact, and allergic contact. Both have similar characteristic signs and symptoms.

The first classification, primary irritant contact dermatitis, is caused by direct exposure to the skin of a chemical or substance that causes irritation either immediately on contact, or within a very short period of time.
It can occur without having had previous exposure to the irritant. Examples of irritant triggers include soaps, cage cleaning chemicals, and some types of oils or phenols found in certain litters such as Cedar and Pine.

In the second classification, allergic contact dermatitis may present as a delayed hypersensitivity which is a T-cell mediated response to an environmental exposure or substance (such as in some food allergies). The allergic response is not generally seen on the first exposure, but rather occurs after repeated exposure over a period of time when each succeeding contact with the irritant begins to set up an ever-increasing sensitivity to it. The results may then manifest as itching, irritation, and inflammation seen on the skin. It is believed, too, that ectoparasites may elicit this type of a response.

Removing the irritating substance in most cases, if known, will help in reducing or clearing up such types as primary irritant contact and allergic contact dermatitis.

Atopic (term applied to an allergic disease) dermatitis

This type of dermatitis is a chronic, immune-mediated, condition of the skin producing an excessive inflammatory response. It is often associated with other types of allergic diseases (e.g. asthma). The cause of atopic dermatitis is unknown, but is believed to be genetically influenced. High serum levels of IgE antibodies are often associated with atopic dermatitis. Contact irritants or food irritants may initiate a response; however, unlike primary contact and allergic contact dermatitis even if the irritant is removed there is often no relief of the symptoms. It is believed that the bacteria staphylococcus aureus (a normal skin flora) exacerbates this condition due to breaks in the skin caused by unrelieved intense itching and subsequent scratching.

Seborrheic dermatitis

Less often seen in rats, this type of dermatitis involves the abnormal production of oil or sebum from the sebaceous glands. The condition causes yellow greasy scaling of the skin with itching and redness. Bacterial and yeast growth that may occur in the oil released from the glands can make curing this condition more difficult. The underlying cause is unknown. It is believed that hormones, fungal infections, or neurological diseases may play a factor.

Ulcerative dermatitis

Often initiated by self-trauma due to a possible allergic response, this type of dermatitis is most often associated with bacterial infection. Culture for bacteria often shows Staphylococcus aureus, although other organisms can be involved.
Lesions are frequently irregular and circumscribed, and often moist. They are found primarily on the shoulders, neck, and rib cage. Itching is often intense and scratching by a rear foot can not only aggravate the lesion but perpetuate it. Destruction of the epidermis along with underlying pustules or abscesses, and granulomatous inflammation, may be present.

In cases where irritants are not known and topical treatment alone does not resolve the dermatitis, a secondary bacterial, yeast or fungal infection could be present that may require antimicrobials to be prescribed by the veterinarian to affect a cure.

For information regarding a more severe form of dermatitis and type of treatments, see: Pyoderma.

Figures

Case Histories and Photos

• Fig. 1: Dermatitis of tail (unknown origin) on two adult female rats (Mus and Knofje)

Diagnostics

Obtain history to determine cause.

Signs of characteristic lesions.

Cultures

Treatment

Eliminate offending substance if able to determine.

Clip toenails of rear feet to prevent further injury to lesions from scratching, or infection.

Consider separating from cage-mates, for a short time, if barbering is preventing healing.

Refer to the Rat Medication Guide for information about any of the following medications used in treatment.

Acute:

• Corticosteroids such as: prednisone or dexamethasone, unless contraindicated.
• Topicals such as: Bacitracin or Polysporin (can be purchased over the counter). The application of creams is preferred to ointments at this stage in order to rehydrate tissue. Dab on skin and rub in thoroughly. Verify appropriateness of topical agent with veterinarian prior to using.

Sub-acute:

• Vitamin E cream, or 1% hydrocortisone cream or ointment (can be purchased over the counter). Dab on skin and rub in thoroughly. Verify appropriateness of topical agent with veterinarian prior to using.
• Antihistamines, such as: diphenhydramine/Benadryl, or Chlorpheniramine/Chlor-Trimeton may be used if pruritus (itching) is present.
  *Note: Synergism can occur when antihistamines and prednisone are used together. Antihistamines are effective for very mild symptoms of itching.

Chronic:

• Vitamin E cream, or 1% hydrocortisone cream or ointment (can be purchased over the counter). Dab on skin and rub in thoroughly. Verify appropriateness of topical agent with veterinarian prior to using.

For involvement of secondary bacterial infection

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.

In addition, the application of a topical (e.g., Bacitracin or Polysporin), or use of a systemic (e.g., Clavamox, cephalexin, or trimethoprim/sulfa) antimicrobial medication may be required. Refer to the Rat Medication Guide.

For involvement of fungal infections

Application of a topical or systemic anti-fungal medication may be required. Refer to the Rat Medication Guide.

*Note:
In those cases where pruritis (itching) is severe, gabapentin can be a useful analgesic having antinociceptive ability.

Nursing Care

• Assess skin daily for improvement of condition or decreased signs of inflammation, irritation, or lesions.
• Wash hands before care and after care to prevent further infection.
• Keep nails clipped.
• 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 until resolved or treatment changed.
• If condition worsens seek advice from a veterinarian.

Outcome

• Itching alleviated
• Lesions resolved
• No secondary infection, or if present, condition controlled

Prevention

• Eliminate use of known litters to cause problems such as Cedar and Pine.
• 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 store 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.
• The freezing of prepackaged or mixed foods and rat blocks prior to feeding is recommended the same as it is for litter/bedding.
• 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.