Chapter 170 Avian Dermatology
Skin and feather disorders are common in companion avian species. Since many of these disorders have a psychological basis, either as the primary cause or as a contributing component, diagnosis and treatment can often be frustrating. A detailed history, physical examination, and assessment of a wide range of diagnostic tests are generally required for diagnosis.
ANATOMY
A basic understanding of normal structure and function of the skin is important.
• The epidermis is composed of three layers: the basal or germinative layer, the intermediate layer, and the cornified layer.
• The dermis consists of the superficial layer and the dermal layer.
• The dermal layer varies in thickness depending on its location on the body. For example, the face is a non-feathered area and therefore is thicker than feathered areas.
• During breeding season, females and some males will develop dermal thickening and neovascularization in the ventral abdominal area. This area is referred to as the brood patch or incubation patch since it contributes to egg incubation. The area should not be confused with an area of feather loss and is a normal finding.
GUIDELINES FOR HEALTHY SKIN AND FEATHERS
• Provide a balanced diet including a wide variety of fresh fruits and vegetables, a pelleted diet, and limited access to seeds.
GENERAL HISTORY AND EXAMINATION
History
• What diet is normally fed and, of this, what does the bird actually consume? Have there been any changes in the diet?
Physical Examination
Perform a thorough physical exam.
• Determine to which of four categories the problem belongs: lack of feather growth, abnormal feather growth, feather destruction, or pseudoproblems (normal changes presumed by the owner to be a problem) (Table 170-1).
DISORDERS OF THE SKIN AND SUBCUTANEOUS TISSUES
Infectious Diseases
Ectoparasites
Knemidokoptes pilae (Scaly Leg and Face Mites)
Etiology
• These mites are most commonly seen in budgerigars, canaries, and finches. They are occasionally reported in cockatiels, Amazon parrots, and other parakeets.
• Infestation can be subclinical until the bird becomes immunosuppressed, similar to demodicosis in mammals.
Clinical Signs
• Lesions begin as hyperkeratosis, crusting, and flaking, eventually progressing to characteristic honeycomb-like encrustations.
Treatment
• Give ivermectin at 0.2 mg/kg SQ, PO, or topically every 2 to 4 weeks for three to four treatments.
• For birds weighing <100 g, applying diluted ivermectin (1 mg/ml) topically to the featherless tract of skin overlying the jugular vein may also be effective.
• If proliferative lesions are excessive, gently debride with a cotton-tipped swab and a small amount of mineral oil.
Viral Diseases
Herpesvirus
• Hyperkeratotic, papilloma-like lesions on the surface of the feet are relatively common in cockatoos and macaws. Lesions are believed to be caused by a herpesvirus, based on histologic evidence of characteristic inclusion bodies or identification of virus on electromicroscopy.
Avian Poxvirus
• Avian pox can cause lesions on the unfeathered skin that can appear ulcerative or as crusts, scabs, or proliferative lesions.
Papillomavirus
• Wart-like lesions on unfeathered areas of the skin have occasionally been reported. Histologically, these lesions resemble those caused by papillomaviruses in other species. However, papillomavirus has only rarely been demonstrated to be the causative agent, and other viruses, such as herpesviruses, can cause similar lesions.
Bacterial Diseases
Bacterial Folliculitis
Etiology
• Primary bacterial folliculitis is unusual in pet bird species. Folliculitis secondary to the trauma caused to the follicle by feather picking may be more common.
Clinical Signs
• Bacterial folliculitis is a rare cause of feather picking but may exacerbate picking if the bird is pruritic.
Diagnosis
• Obtain one or more small skin biopsy specimens that include an affected follicle. When obtaining a biopsy specimen, keep in mind that avian skin and subcutis are extremely thin as compared with that of mammals. Submit biopsy specimens for histologic examination and culture and susceptibility testing.
• In some cases, samples for culture can be obtained via sterile aspiration of perifollicular swelling.
Chronic Ulcerative Dermatitis
Etiology
• The cause is unknown but has been anecdotally associated with giardiasis in cockatiels, an unidentified virus in lovebirds, and hypovitaminosis E in other species. Environmental, behavioral, and hormonal factors may also play a role.
Clinical Signs
• Disease is most commonly seen lovebirds, cockatiels, grey-cheeked parakeets, Quaker parrots, Amazons, and cockatoos.
• Lesions usually are found in the ventral wing web area and lateral body wall underneath the wing or around the neck, but they can be seen in any area.
Treatment
• Aggressive systemic antibiotic treatment is usually warranted. Sepsis may occur in untreated birds. Base selection on results of culture when possible. Pending culture, administer broad spectrum antibiotics that are effective against Staphylococcus spp., such as enrofloxacin (Baytril, Bayer), 7.5 to 15 mg/kg PO or IM q12h, or ceftazidime (Fortaz, Glaxo), 75 to 100 mg/kg IM q6-8h. Treatment for 4 to 6 weeks may be necessary.
• In some birds, especially cockatiels, lesions respond well to empirical treatment with metronidazole (Flagyl, Searle), 10 to 30 mg/kg PO q12h for 10 days. Treatment success may be due to underlying giardiasis or may be the result of the antimicrobial or anti-inflammatory effects of metronidazole.
• Apply topical silver sulfadiazine 1% cream (Silvadene, Marion Merrell Dow) or mild topical astringent such as Domeboro solution.
Avian Tuberculosis
• Cutaneous mycobacteriosis is unusual in pet birds. Lesions are usually caused by mycobacterium avium and can be an extension of systemic disease.
• Lesions usually appear around the head and neck. Most appear as subcutaneous swellings but may appear wart-like or ulcerated.
• Perform a skin biopsy or cytologic examination with acid-fast staining or polymerase chain reaction to identify mycobacterium.
Neoplasia
Squamous Cell Carcinoma
Clinical Signs
• The most common sites affected include the back, uropygial gland, and wings. Oral mucosa, including the crop and esophagus, can also be affected.
Lipoma
Etiology
• A diet high in fat and limited exercise seems to contribute to formation of lipomas. Tumors are most commonly found on obese birds. Hypothyroidism may play a role.
Diagnosis
• Palpate for one or more well-delineated, soft, fluctuant masses. Masses may appear white or yellow through the skin.
Treatment
• Many lipomas will respond to dietary changes. Place the bird on a low-fat diet, restrict the amount of food offered, and increase exercise.
• Surgery may be indicated if the masses interfere with movement, become ulcerated, or become infected or if the bird is picking at the mass. Complete excision can be difficult if the masses are large.
