Enfermedades Virales de la Piel en Gatos

Cutaneous viral dermatoses are rare in feline medicine. Moreover, these dermatoses are frequently underdiagnosed because it is difficult to identify an exact causative agent. These notes will focus on skin disorders associated with papillomavirus, feline herpesvirus, feline calicivirus, feline leucemia virus, feline immunodeficiency virus and feline poxvirus infections.

Papillomavirus-Associated Dermatoses

The great majority of clinical cases described of papillomavirus infection in domestic cats are associated with FdPV2.

This infection initially manifests as viral plaques, which typically appear as multiple, scaly plaques of variable size (usually less than 8 mm in diameter) that are sometimes hyperpigmented.

Histopathology is mandatory to confirm the diagnosis. Cytopathic changes, such as nuclear shrinkage, koilocytosis, and increased quantities of blue-grey foamy cytoplasm, are often present in keratinocytes within the plaques. Nonetheless, viral etiology may be confirmed via immunohistochemistry or PCR.

It is suggested that viral plaques are the precursory lesions of the so-called Bowenoid in situ carcinomas. In fact, DNA of FdPV-2 is frequently present within feline Bowenoid in situ carcinoma.

Immunohistochemical staining resulted in positive nuclear staining of cells within the granular cell layer in 28 out of 63 cases reported and primers designed to amplify FdPV-2 detected PV DNA within 20 of 20 Bowenoid in situ carcinomas in another study.

Numerous anecdotal reports suggest the use of an immune response modifier (imiquimod; Aldara, 3M Health Care Limited) when applied topically three times a week. Typical warts and cutaneous horns have also been described in association with PV infection in cats, but they are probably very rare. Another papillomavirus infection in cats is represented by the so-called feline "sarcoid". This refers to PV-induced fibroblastic proliferations, induced by the feline sarcoid-associated PV (FeSarPV), which infects fibroblasts rather than keratinocytes. Feline sarcoid develops in free-roaming young cats in rural areas, and half of the reported cases were known to have been exposed to cattle because of the cross-species infection. Lesions are slow-growing solitary or multiple nodules that may measure up to 2 cm in diameter. These exophytic masses may be pedunculated and are often ulcerated. They are most commonly located on the head, neck, tail, and digits. Diagnosis is histologically. Lesions show a dense proliferation of fibroblastic cells with epidermal hyperplasia in a rete-peg configuration.

Feline Herpesvirus Dermatitis

FHV-1 infection in cat generally causes acute upper respiratory disease as well as conjunctivitis and stomatitis. The main target tissue is the respiratory epithelium, however, the epidermis and follicular epithelia are also affected.

After airborne infection, the virus multiplies in the upper respiratory mucosa and tonsils and remains latent in the trigeminal ganglion. Reactivation may occur spontaneously, however, it is more likely after stress or pharmacological treatment (glucocorticoids or cyclosporine). This reactivation may result in skin lesions. Herpes dermatitis affects mainly the face and is characterised by erosions, ulcerations and crusts.

Pruritus is variable but usually present. Therefore, this dermatitis is a differential diagnosis of allergic dermatitis. FHV-1 associated dermatitis must be rule out before making an eventual diagnosis and treatment of allergy. The diagnosis is based on dermatopathological examination, however, intranuclear inclusion bodies are difficult to be observed, especially in very necrotic skin. Therefore, more sensitive techniques are necessary in order to confirm viral infection (immunohistochemistry assay or PCR analysis). PCR results must be interpreted with caution. A positive result may be due to a true skin infection or due to secondary contamination from infected oral mucosa through licking.

Treatment is based on the combined use of famciclovir and L-lysine, although the effectiveness of the later remains highly controversial.

There is some evidence that herpesvirus may be implicated in erythema multiforme in the cat.

Cowpox Virus Infection

Feline cowpox infection is characteristic of rurally hunting cats. The primary lesion is usually a rodent (natural host) bite wound located on the head, neck or forelimb. In early stages there is fever, anorexia, depression and diarrhea. Within a few days to weeks, cats develop more widespread eroded nodules, papules or plaques. The diagnosis is by means of histopathology with demonstration of intracytoplasmatic eosinophilic inclusion bodies. There is no specific therapy, and the prognosis is good with spontaneous resolution after 3–8 weeks. The infections can be transmitted to other cats, dogs or humans. All affected cats should be handled with caution and isolated until the lesions heal.

Feline Leucemia Virus-Associated Dermatoses

FeLV infections in cats may be associated to different skin problems.

It can induce skin tumours such as lymphoma and fibrosarcoma. Other clinical problems may include chronic or recurrent infections such as dermatophytosis, demodicosis, bacterial infections and Malassezia dermatitis.

One giant cell dermatosis has been described associated to typical giant keratinocytes and positive immunohistochemistry. Clinically this entity is characterised by a pruritic-crusted dermatosis mainly on the head.

Single or multicentric cutaneous horns in the centre of digital, central or metacarpal/metatarsal pads, and sometimes on the face have also been described on infected cats. However, causality has not been proven.

To date, no treatment has proven effective in eliminating FeLV infection.

FIV Infection

This virus does not induce specific skin changes but leads to sever immunodeficiency that may favour the development of opportunistic infections such as pyoderma, demodicosis, dermatophytosis, Malassezia dermatitis, mycobacteriosis or leishmaniosis.

Calicivirus Infection

This viral infection is usually associated with conjunctivitis and stomatitis, and rarely with skin disease (ulcers on nasal planum and lips). However, less classical syndromes associated with this virus have been described recently probably due to mutations. This more highly virulent strains are associated with subcutaneous edema of the face and limbs and ulcerative dermatitis on the face, especially nose, and distal part of the extremities and pads along with varying degrees of pyrexia, anorexia, and jaundice.

Pustular dermatitis has been also reported on the abdomen of two cats suddenly after ovariohysterectomy.

Diagnosis is histological, which reveals cytopathic effects of virus. Immunohistochemistry detects viral antigen on the cytoplasm of keratinocytes.

The prognosis is usually good for non-virulent systemic disease. However, up to 50% of cats affected by virulent strains die or are euthanized in extremis.

Feline Coronavirus Infection

Viral infection with feline coronavirus progressing to feline infectious peritonitis has been reported to cause cutaneous vasculitis lesions.

References

1.  Greene CE. Infectious Diseases of the Dog and Cat. 3rd ed. Philadelphia, PA: WB Saunders Co; 2006.

2.  Miller WH, Griffin CE, Campbell LK. Muller and Kirk's: Small Animal Dermatology. 7th ed. Philadelphia, PA: WB Saunders Co; 2013.

3.  Gross TL, Ihrke PJ, Walder EJ, Affolter VK. Skin Diseases of the Dog and Cat, Clinical and Histopathologic Diagnosis. 2nd ed. Oxford, UK: Blackwell Science Ltd; 2005.

4.  Nagata M, Rosenkrantz W. Cutaneous viral dermatoses in dogs and cats. Compend Contin Educ Vet. 2013;35:E1–E10.

5.  Egberink H, Thiry E, Mostl K, et al. Feline viral papillomatosis. ABCD guidelines on prevention and management. J Feline Med Surg. 2013;15:560–562.