Interpreting Canine Bacterial Dermatitis

During adolescence our male puppy, Rocky, developed "pimples" under his chin and a rash along his groin. We were advised that these conditions were nothing more than "puppy acne" that would clear up as he matured.

Rocky matured but was still plagued by recurring chin pustules and an increase in the frequency of pus rashes in his groin area. By two years of age he had also developed a persistent infection in his elbow calluses, an inflamed condition between his toe pads and interdigital "cysts" on the top of his front feet. A variety of antibiotics, topical therapy and minor surgical procedures had been prescribed and attempted with poor results.

It was not until he began having difficulty walking -- due to the condition of his feet -- that we were sent to a veterinarian who specialized in dermatology. Rocky was diagnosed as having deep pyoderma, which is a bacterial disease of the skin. In Rocky's case it was chronic and recurrent.

Before the final diagnosis, we found it difficult to understand the whys and wherefores of Rocky's declining condition. His symptoms had been dealt with as isolated problems, such as ingrown hair, fungus, hormone imbalance, sebaceous cysts, food allergy, atopic allergy, thyroid conditions -- the possible causes were endless, as were the inconclusive tests that had been done to determine a proper diagnosis.

The confusion we experienced in trying to understand Rocky's variety of problems was unnerving. It had never occurred to us that the symptoms indicated a generalized problem, and that they were all associated with a particular disease. We had also never thought of seeking the help of a dermatologist, mostly because we were unaware that dermatology was a specific practice within the veterinary field. Until that time, Rocky's symptoms were diagnosed as everything except a generalized skin problem.

In order to grasp the nature of Rocky's illness, we had to become familiar with the etiology of bacterial dermatitis. With the generous help of Dr. Gene Nesbitt, DVM, MS, the veterinary dermatologist who treated Rocky and authored and edited the textbooks I researched, and by making extensive use of Taber's Cyclopedic Medical Dictionary, I was able to interpret and understand the medical textbooks. The following is a layperson's interpretation.

Canine skin consists of two primary layers: the epidermis and the dermis. The epidermis (outer layer) is composed of four layers: stratum corneum, stratum granulosum, stratum spinosum and basal cell layer. Also included in the epidermis are hair follicles, apocrine (sweat) glands and sebaceous (oil-secreting) glands which project into the underlying skin layer known as the dermis.

The dermis is located between the epidermis and subcutis. It consists of a loosely molded assemblage of connective tissues which contain blood vessels, nerves, lymphatics, glands and muscles.

Pyoderma

Pyoderma is the medical term used to denote infections of the skin caused by bacteria, defined as a pus-producing infection. Despite the definition, pus is not always visible nor is the presence of pustules (small elevation of skin filled with lymph or pus), always indicative of pyoderma. It is a common disease in dogs, although the diagnosis and management of it are often difficult due to the overlapping of symptoms, which indicate infection by different types of bacteria.

Cause of Bacterial Disease

Bacterial flora that normally inhabit healthy skin are referred to as residents; they are able to live and multiply within the skin's environment without being the primary cause of infection. Transient bacteria cannot exist harmoniously with the skin; they are commonly implicated as the cause of infection.

The primary bacteria responsible for most canine pyoderma are the transient coagulase positive staphylococcus. While coagulase-positive staphylococcus usually are not cultured from normal dog skin, these organisms are found on 90% of normal dogs' hair coats, thus a population of potential disease-causing bacteria exists when factors such as seborrhea, parasites, immune incompetence, endocrine imbalance or trauma predispose the skin to infection.

Pyoderma Classification

Pyoderma are classified as surface, superficial or deep. The origination and development of any of the three types of pyoderma depend on three major factors; the actual disease-causing properties of the invading bacteria; the route of entry the bacteria used to penetrate the skin; and the action or reaction of the animals' immune system toward the bacteria.

Surface Pyoderma

Surface pyoderma are bacterial infections confined to the surface of the skin. Two of the most common types are pyotraumatic dermatitis and skin fold dermatitis.

Pyotraumatic dermatitis, (acute moist dermatitis -- more commonly known as "hot spots") is typically located on the back near the tail, the outside thighs and the shoulder. Occasionally the neck and face are also involved. It is typified by localized itching, reddened skin patches and ulcerated oozing lesions. Longhaired breeds are more commonly affected, with a marked increase of incidence during warm weather.

Contributing factors are allergies, parasites and poor grooming. Flea allergy dermatitis is one of the most common causes of "hot spots". Successful treatment depends on identifying and controlling the "itch". Short-term oral corticosteroid therapy can be used to control itching, while keeping the affected area clean. Topical therapy is optional.

Skin fold pyoderma is associated with moisture and accumulation of debris. The environment in the crease of the fold is ideal for bacterial growth. Skin abrasion, lesions, hyperkeratosis and hyperpigmentation are commonly seen when itching has been a problem. The degree of skin damage varies with each type of skin fold; reddening of the skin, ulceration and oozing are common in most instances.

Treatment is usually accomplished using a 2.5 to three percent benzoyl peroxide shampoo. Initial application should be daily, with eventual maintenance cleansing two to three times weekly. Systemic antibiotics are seldom needed.

Superficial Pyoderma

Superficial pyoderma are bacterial infections which present themselves beneath the stratum corneum layer of the epidermis. Commonly called superficial folliculitis, the bacterial diseases within this group have been termed recurrent pyoderma, pruritic pyoderma, shorthaired dog pyoderma, staphylococcal allergy and bacterial hypersensitivity. All of these have similar symptoms and require similar treatment. Systemic antibiotics are appropriate therapy.

Superficial folliculitis is characterized by reddened pustules that develop a flattened crust usually five to ten millimeters in diameter. When the crust loosens, the center falls off and a thin circle of epidermal tissue (resembling a collar) remains around the periphery of the lesion. The ensuing area of skin is usually bald and hyperpigmented. It is common to have all stages of infection present at the same time.

Shorthaired dog pyoderma has a high concentration of pustules in a less extensive area -- usually the outside thighs and along the back and top of the neck. Dogs diagnosed as having shorthaired pyoderma suffer from thinning of the hair coat over the affected area.

Recurrence is common in superficial folliculitis. In cases where superficial pyoderma is diagnosed as chronic and recurrent, a genetic predisposition is suspected. In these cases, owners are left with the possibility of lifelong intermittent antibiotic therapy.

Deep Pyoderma

Deep pyoderma is a serious disease involving follicular (follicle -- a small secretory sac or cavity) ruptures caused by bacterial infection that extends to the dermis. The lesions may be localized or generalized, and often appear on the face, feet and pressure points. Deep pyoderma may include pressure point, nasal, interdigital, muzzle and chin, and generalized varieties.

Pressure point pyoderma is usually found in the large and giant breeds. The elbows, hocks, toes and outside stifles are most commonly affected. It is characterized by an increase in callous surface, persistent oozing, crusting and wearing away of the skin. Whirlpool baths of povidone iodine or chlorohexidine, and appropriate antibiotics are the indicated therapy. Providing the animal with soft bedding is also helpful.

Nasal pyoderma is characterized by painful swelling of the tissue on top of the nose, erosion of the skin, ulceration and crusting. Antibiotics and wet soaks are appropriate therapy.

Interdigital pyoderma -- often erroneously referred to as "interdigital cysts" though no cyst structure is present -- is located between the toes and pads of the feet. It is a type of cellulitis (a condition where inflammatory fluids are forced into the tissues, rather than being discharged on the surface) that is characterized in the active stages by deep draining tracts of large pustules in one or more interdigital spaces.

Due to the potential chronic nature of interdigital pyoderma, a thorough search for underlying causes is essential. All cases of interdigital pyoderma require skin scrapings, bacterial cultures and sensitivity tests. If no underlying cause is determined for persistent interdigital pyoderma, a genetic predisposition is suspected, and intermittent lifelong antibiotics will usually affect control of the symptoms.

Muzzle and chin folliculitis -- furunculosis -- is often erroneously referred to as canine acne. A form of pustules is generally seen in young dogs; however, mature dogs which exhibit symptoms of pustular pimples are usually afflicted with a chronic condition.

Generalized deep pyoderma is a very severe disease involving the entire body. The lesions constitute large reddened bald areas that drain. The surrounding skin is easily crumbled, and the animal is frequently feverish and depressed. Antibiotic therapy is usually long term (six to eight months).

In cases where pyoderma is diagnosed as chronic and recurring, a genetic predisposition to bacterial infection is usually present. A general tendency toward pyoderma is seen in certain breeds, with a strong tendency showing up in specific lines. It is not uncommon for these animals to exhibit clinical signs of more than one form of pyoderma at any one time. These dogs will often need intermittent lifelong antibiotic treatment.

Rocky's general health had been on a decline. His inadequate immune system was not capable of fighting off the barrage of disease-causing bacteria he encountered. Constant cellulitis due to interdigital pyoderma caused a deformity of his toe pads and permanent lameness in his front feet. The swellings in between his toes would rupture and swell again. Large running pustules were a constant problem on his elbow pads and chin, resulting in severe scarring.

After proper diagnostic testing was done, the antibiotic Cephradine (Velosef, E.R., Squibb & Sons) was prescribed. Within three weeks Rocky's chin and elbows had cleared up, and a distinct improvement was seen in his feet. A surgical procedure was necessary to eliminate the infection from his right front foot due to a heavy accumulation of scar tissue, which prevented penetration of antibiotics carried in the blood.

It took Rocky a year to regain his health. He will always have recurrences of pyoderma of one form or another due to a genetic predisposition to bacterial infection. But at least now that we understand his disease, we are able to recognize and treat any new symptoms before they get out of hand.

In cooperation with the American Academy of Veterinary Dermatology, research is being done to determine a hereditary base for the problem of bacterial dermatitis in Mastiffs. Mastiffs have been chosen as the forerunner for research because preliminary studies indicate a possible hereditary predisposition to recurring bacterial skin infections.

Once a suitable format for research and presentation has been established, additional breeds can be studied. Case histories and pedigrees of dogs, both living and deceased, afflicted with any form of bacterial infections are needed. Pedigrees are most important to this study, as they provide the only means of researching a hereditary base.

Please send case histories and pedigrees to: Deborah Ahlers, 1 Bacon Rd, St. James, NY 11780. Any correspondence for the American Academy of Veterinary Dermatology should be addressed to: Dr. Gene Nesbitt, AAVD Chairman, Nesbitt Veterinary Associates, 706 Bloomfield Ave., West Caldwell, NJ 07006. All Mastiff clubs have been invited to comply.

References

Ihrke, P.I. and White, S.D. Contemporary Issues in Small Animal Practice, 
Dermatology, Vol. 8 (Nesbitt, G.H., editor), Churchill Livingstone, New York, 1987.

Nesbitt, G.H. Canine and Feline Dermatology: A Systematic Approach, 
Lea & Febiger, Philadelphia, 1983.

Editors Note ... Lisa

I called Deborah for an update on "Rocky's" condition. "Rocky" lived a normal lifespan, but he was never cured of his disease. He was a very handsome, typey Mastiff, and a successful show dog.

He was neutered, despite protests by other breeders who wanted to use him at stud.

After neutering, his outbreaks slowed in frequency to twice a year (spring and fall). His treatment was extremely expensive -- over $300 per month for antibiotics, for many months at a time.

Deborah was able to trace this disease in "Rocky's" background to prove to her complete satisfaction that it was hereditary.

Thank you Deborah!