Rudayna Ghubash,     Marina del Rey, California

Feline Herpesvirus 1

Feline herpesvirus type 1, a virus in the Herpesviridae family, is a common cause of respiratory illness, conjunctivitis, stomatitis, and corneal ulceration in feline patients. The majority of cats that contract this virus become asymptomatic carriers harboring the virus in the trigeminal ganglia. Symptoms commonly recur when these animals experience stress such as moving, entering multicat households, boarding, becoming pregnant, undergoing surgery, or receiving glucocorticoids. In the cases reported in the literature, there has not been a causal link between this condition and infection with feline leukemia virus or feline immunodeficiency virus.

It has been demonstrated that infection with feline herpesvirus 1 can manifest as dermatologic lesions in the absence of concurrent ophthalmic or respiratory symptoms in domestic cats and in cheetahs. There does not appear to be an age, breed, or sex predilection. Skin lesions typically follow the path of the trigeminal nerve on the haired surface of the face and nasal planum, although the ears, feet, and ventrum also can be affected. The lesions are characterized by an ulcerative, erosive, crusting dermatitis that also can display marked erythema and swelling. Because of shedding of the virus, skin lesions often are noted to be in the location of lacrimal and salivary secretions. Feline herpesvirus infection also can be an underlying trigger of erythema multiforme in the cat with absence of the ulcerative, erosive lesions described here.

Differential diagnoses for feline herpesvirus infection include allergic disease, mosquito bite hypersensitivity, squamous cell carcinoma, eosinophilic granulomas complex lesions, pemphigus foliaceus, and idiopathic ulcerative dermatitis of Persian cats.

Diagnosis of the infection is made with a combination of histopathologic evaluation, immunohistochemical (IHC) testing, and polymerase chain reaction (PCR) assay of skin samples. Histopathologic findings include necrosis and ulceration of the epidermis extending into the dermis. Hair follicles and the perivascular dermis usually are inundated with a mixed inflammatory cell dermatitis, with a significant eosinophilia. Although they can be difficult to find, intranuclear viral inclusions in the superficial and follicular epithelium can be appreciated, and IHC and PCR testing can be performed to confirm that these are herpesvirus 1 inclusion bodies. If inclusion bodies are not seen, PCR and IHC analysis can be used to detect feline herpesvirus in tissue, with IHC evaluation being the preferred diagnostic test (Persico et al, 2011). It is not useful to perform PCR testing on serum or mucocutaneous samples alone, since many cats have been exposed to the virus and a positive result on serum testing may be an incidental finding and not confirmation of a diagnosis.

Feline herpesvirus infection can be misdiagnosed easily as an eosinophilic granuloma complex lesion or another eosinophilic dermatosis. Herpesvirus infection should be considered if the patient does not respond well to treatment for these latter conditions or if there is a concurrent history of upper respiratory tract viral disease. If this is the case, IHC testing can be used to detect feline herpesvirus in tissue (Lee and Bosward, 2010).

Cutaneous manifestations of feline herpesvirus infection can be difficult to resolve, and the prognosis is guarded. Several treatment options are available that can manage, although not always cure, this condition. L-lysine, which inhibits herpesvirus replication by blocking the availability of the amino acid arginine, can be effective at a dosage of 200 to 500 mg per cat twice daily PO. Interferon-α (IFN-α), a cytokine with antiviral properties, also has been used to treat this virus, but the dosages reported in the literature vary widely. Dosages ranging from 30 U per cat daily PO to 250 to 500 units per cat three times weekly PO and 10,000 U/kg twice daily SC have been reported, with the 30-U/day dosage used most commonly for dermatologic conditions. Treatment with famciclovir has been found to improve clinical signs in cats infected with feline herpesvirus 1, both naturally and experimentally; reported dosages are 90 mg/kg/day, 62.5 mg per cat once or twice daily, and 125 mg per cat three times daily. Imiquimod, a topical cream for the treatment of human genital warts caused by papillomavirus, can be effective in these cats when applied every 48 to 72 hours. Localized erythema can occur with imiquimod administration. Topical and oral glucocorticoids are contraindicated.

Feline Calicivirus

Feline calicivirus (FCV), a virus in the Caliciviridae family, is a common cause of ocular discharge, nasal discharge, oral ulceration, and conjunctivitis in felines. It has been isolated from some cats with feline chin acne, although it is unknown whether this was an incidental finding. Twenty-five percent of animals that are infected with this virus become long-term carriers and experience relapse with clinical symptoms when faced with stressful situations, as with feline herpesvirus infection.

An unusual localized, pustular version of calicivirus dermatitis has been reported in two young vaccinated cats following routine ovariectomy (Declercq, 2005). Both cats developed lethargy, decreased appetite, and a localized pustular dermatitis at the spay incision site within days of their surgeries. Histopathologic analysis of affected abdominal skin from both cats revealed a panepidermal pustulosis and necrotizing dermatitis, with IHC testing confirming the presence of FCV antigen. One cat was treated with amoxicillin/clavulanic acid and ketoprofen with no improvement but then improved significantly when prednisolone 2 mg/kg was administered. The cat was weaned off the prednisolone and recovered fully. The second cat was treated with amoxicillin/clavulanic acid, ketoprofen, and enrofloxacin but developed pleural effusion and severe dyspnea and was euthanized.

A severe hemorrhagic, virulent form of FCV has been reported that produced a mortality rate of 33% to 60% (Pesavento et al, 2004). Systemic signs exhibited by these cats included fever, anorexia, and diffuse edema. An ulcerative, crusting dermatitis of the face, ears, and feet also was present in many symptomatic animals. Histopathologic evaluation of skin lesions demonstrated necrosis of the epidermis and ballooning degeneration of the epidermis, and IHC testing identified the presence of FCV antigen. Many affected cats were up to date on their calicivirus vaccinations, but it appeared that prior vaccination was not protective against the viral strain causing their illness. Management consists of supportive care, and at this time no effective treatment for the hemorrhagic, virulent form of this disease has been developed and mortality rates remain high.