Overview

• Dermatoses caused by viral infection within keratinized structures.
• Viral replication within keratinized structures may cause cytosuppressive effects or upregulate keratinization resulting in hyperplastic or crusted conditions.

Signalment

• Dogs and cats
• Uncommon dermatoses
• No breed, sex, or geographic predilections reported
• No genetic basis for these diseases
• Young to young adult dogs
• Cats of any age

Signs

• Facial involvement or involvement of the head is common.
  • Lesions are often asymmetrical in distribution.
• Paws and/or paw pads may be affected as well as other mucocutaneous junctions.
• Acute or gradual onset; lesions may be associated with the history of a bite wound or fight.
• Variable pruritus; can progress to self-mutilation with some viral infections.
• Crusts.
• Associated superficial bacterial folliculitis.
• Abscess.
• Paronychia.
• Poor wound healing.
• Seborrhea.
• Exfoliative dermatitis.
• Cutaneous horns.
• Gingivitis/stomatitis.
• Cutaneous or oral ulceration.
• Nasodigital hyperkeratosis.
• Impetigo in young dogs, without expected inflammation.
• Pigmented macules or plaques.
• Progression to bowenoid in situ carcinoma (FIV, papillomavirus).
  • Multiple mast cell tumors (FIV).
  • Systemic signs of illness may be present.
  • Signs consistent with an upper respiratory infection may or may not be present prior to the development of skin lesions.

Causes & Risk Factors

• FeLV
• FIV
• Feline cowpox virus infection
• Feline infectious peritonitis
• Feline papillomavirus
• Canine papillomavirus
• Canine distemper
• Contagious viral pustular dermatitis (orf [parapoxvirus])
• Pseudorabies (-herpesvirus)
• Feline rhinotracheitis infection (-herpesvirus-1)
• Feline calicivirus infection
• Fighting or hunting behavior, multiple animal households, exposure to infected animals, and/or ingestion of infected material increases risk of exposure.

Differential Diagnosis

• Crusting diseases-if crust formation precedes other symptoms, consider drug eruption, actinic keratoses, pemphigus foliaceus, systemic lupus erythematosus, other causes for exfoliative dermatitis.
• Allergic disorders-usually pruritic: flea allergic dermatitis, cutaneous adverse reaction to food, or atopic dermatitis. Feline herpesvirus dermatitis lesions can mimic lesions of the eosinophilic granuloma complex and are also pruritic. Skin biopsy may not distinguish the syndromes unless viral inclusion bodies are present.
• Parasitic diseases-canine and/or feline scabies, demodicosis, cheyletiellosis.
• Infectious diseases-superficial and deep bacterial and fungal infections, leishmaniasis.
• Dogs-zinc deficiency syndromes, hepatocutaneous syndrome, nasal hyperkeratosis.
• Neoplasia-with extensive crusting and ulceration; squamous cell carcinoma, mast cell tumor, and epitheliotropic lymphoma.

CBC/Biochemistry/Urinalysis

Nonspecific

Other Laboratory Tests

• Skin biopsy-necessary to prove viral origin of skin lesions; not always conclusive. If considering herpesvirus dermatitis, inform pathologist of suspicion.
• Virus isolation.
• Serology-confirms FeLV, FIV, or other viral infection.

Imaging

N/A

Diagnostic Procedures

• Skin scrapings, trichograms-parasitic infestations.
• Dermatophyte culture-fungal infections.
• Epidermal cytology-bacterial folliculitis.
• Skin biopsy is the definitive diagnostic test.
• Immunohistochemical staining for viral particles.
• Viral serology and/or PCR.

Pathologic Findings

• Irregular hyperplasia.
• Ballooning degeneration.
• Hydropic interface dermatitis.
• Syncytial-type giant cell formation within the epidermis and/or outer root sheath of the hair follicle with associated apoptotic keratinocytes.
• Keratinocyte inclusion bodies.
• Epidermal ulceration with dermal necrosis, necrosis of epitrichial sweat glands, neutrophilic and/or eosinophilic inflammation.

Drug(s)

• Supportive care and treatment of secondary infections.
• Cats-herpesvirus: L-lysine 200–500 mg/cat q12h; interferon- 30 units/cat/day orally, famcyclovir 125 mg q12h, use of topical acyclovir has been reported.
• Cats-bowenoid in situ carcinoma: imiquimod.
• Dogs-individual papillomas–surgical excision; imiquimod.

Contraindications/Possible Interactions

Immunosuppressive therapies.

Patient Monitoring

Varies based upon viral infection and presence or absence of systemic involvement.

Prevention/Avoidance

Prevent hunting behavior and exposure to potentially infectious materials and infected animals.

Possible Complications

Bacteremia and septicemia

Expected Course and Prognosis

• Skin lesions may not respond to therapy.
• Systemic signs may eventually develop as a result of viral infection.
• Dependent upon the causal virus, animals may self-cure.
• In cats, papillomavirus infection may progress to bowenoid in situ carcinoma.

Associated Conditions

N/A

Age-Related Factors

Dependent on viral cause.

Zoonotic Potential

Feline cowpox virus and contagious viral pustular dermatitis (parapoxvirus) can be transmitted to other dogs, humans, and cats.

See Also

• Canine Distemper
• Feline Calicivirus Infection
• Feline Herpesvirus Infection
• Feline Immunodeficiency Virus Infection (FIV)
• Feline Leukemia Virus Infection (FeLV)
• Papillomatosis

Abbreviations

• FeLV = feline leukemia virus
• FIV = feline immunodeficiency virus