Papillomaviruses (PVs) are small DNA viruses that induce benign and/or malignant epithelial tumours in different species, including the domestic cat (Felis catus). To date, five F. catus papillomavirus genotypes have been identified (FcaPV-1 to FcaPV-5). FcaPV-1 is associated with skin and oral benign lesions, while FcaPV-2 infection is widely associated with feline squamous cell carcinomas.
Solitary lesions have been reported in North America, Australia and Europe. Histopathologically, they appear similar to equine sarcoids, and have been termed feline sarcoid, but a feline specific virus is incriminated (feline papilloma virus-1). Papilloma virus appears to be more common in immunocompromised cats (concurrent infection with FeLV and FIV has been reported).
PV-containing lesions have been reported in six feline species: the domestic cat (Felis domesticus), bobcat (Lynx rufus), Florida panther (Puma concolor coryi, previously named Felis concolor coryi), Asian lion (Panthera leo persica), snow leopard (Uncia uncia, previously named Panthera uncia), and the clouded leopard (Neofelis nebulosa). To date, the Felis domesticus PV type 1 (FdPV1) is the only feline PV that was isolated and completely genomically characterized.
Papilloma virus infections usually manifest as crusty plaques and secondarily infected ulcers on the face, limbs and trunks. Lesions are often pruritic and self-trauma results in secondary bacterial infections. Multiple, hyperplastic plaques, have been seen in old Persian cats and in other cats, one of which was FIV-positive. These lesions, which are sometimes hyperpigmented, occur mainly on the trunk.
An association between feline papilloma virus and multicentric squamous cell carcinoma (Feline bowenoid in situ carcinoma) has been reported. These occur in cats more than 10 years of age and some of them have been reported to be FIV-positive. Clinically they are characterised by papules, nodules and even hyperkeratotic plaques which can become ulcerated. Lesion distribution is multicentric but involves the face, shoulders and limbs.
The histology of feline fibropapillomas and equine sarcoids is virtually identical, characterized by a fibroblastic proliferation with overlying epithelial hyperplasia and rete ridges. Electron microscopy confirms the fibroblastic nature of the neoplastic cells.
In one study of 20 affected cats, eleven had known exposure to cattle and all but one were submitted from veterinary clinics in Wisconsin, a state known for its dairy farms. Nine cats did not have confirmed exposure to cattle but may have been exposed unbeknownst to the clinician or owner, i.e., prior to living with the present owner.
Fibropapilloma and feline sarcoids need to be distinguished from fibrosarcoma, but histopathology is required to confirm this. Feline bowenoid in situ carcinoma have a similar appearance, as do nasal squamous cell carcinoma.
The low incidence of feline cutaneous fibropapillomas is related to the tranmission of the virus from cattle. Cats that have greater contact with cattle, i.e., farm cats, may not be biopsied often. In addition, the molecular techniques for identifying viral DNA in these tumours have only recently become available. Any or all of these factors may contribute to the paucity of reports of feline fibropapillomas.
Based on immunohistochemistry, electron microscopy, and molecular tests, the papillomavirus in feline cutaneous squamous papillomas has been considered to represent Felis domesticus papillomavirus-type 1; however, results of DNA sequencing have not been reported. Squamous papillomas appear to affect immunodeficient cats. Two of the older cats with fibropapillomas had concomitant disease (lymphoma in one and feline immunodeficiency virus infection in another) that may well have caused immunosuppression. It seems logical that immunosuppression might play a role in viral oncogenesis and apply to both manifestations of cutaneous papillomavirus infection, i.e., squamous papilloma and fibropapilloma.
No specific therapy has attempted apart from topical therapy.
Treatment with imiquimod 5% cream showed some response. Most cats (75%) in this trial developed new lesions. New lesions also responded to imiquimod 5% cream in all cats treated. Five cats (41%) had side effects suspected to be associated with the use of imiquimod 5% cream, including local erythema (25%), increased liver enzymes and neutropenia (8%), and partial anorexia and vomiting (8%).
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