Feline herpesvirus-1-associated dermatitis: viral load assessment by real time PCR for diagnostic purposes

Feline herpesvirus-1 (FHV-1)-associated dermatitis is a facial and nasal ulcerative and necrotic disease. Its clini- cal presentation overlaps with that of other feline der- matoses including hypersensitivity disorders, therefore providing a correct diagnosis is required to rapidly start antiviral therapy. Histopathological diagnosis relies on the detection of nuclear inclusion bodies but their rarity may lead to misdiagnosis. The aim of this study was to use real time PCR (qPCR) for the diagnosis of FHV-1- associated facial dermatitis. We conducted a retrospec- tive histopathological study with 25 paraffin-embedded feline skin samples. Based on histopathological features, we separated the cases in four groups: Group 1: sam- ples with a diagnosis of herpesvirus dermatitis (seven cats); Group 2: samples with nonherpetic facial dermati- tis (six); Group 3: samples with facial dermatitis of ambiguous nature (allergic or viral) (eight), and, Group 4: samples from apparently healthy cats (four). We expressed qPCR results as the number of copies of viral gene per copy of Felis catus housekeeping genes (DDCq). All specimens from the Group 1 showed DDCq >20,000, while for specimens belonging to Groups 2 and 4 the DDCq was <2,000. In Group 3, two samples showed high values of DDCq that were comparable to those of Group 1, three had DDCq <2,000 and three samples had negative results. Our qPCR results corre- lated well with histopathology results for Groups 1, 2 and 4 samples, thereby indicating that this qPCR method can be used for the diagnosis of FHV-1-asso- ciated dermatitis; values <2,000 might indicate a latency of the virus