Dermal inflammatory vascular changes associated with felid alphaherpesvirus 1 dermatitis in cats

Feline ulcerative dermatitis is an uncommon disease of domestic and wild cats associated with felid alphaherpesvirus 1 (FeAHV1) infection. Here we report dermal inflammatory vascular changes with or without thrombosis in six of eight cats with feline ulcerative dermatitis. Submissions were searched retrospectively from the Athens Veterinary Diagnostic Laboratory biopsy archives between 2010 and 2025. FeAHV1 infection was confirmed by immunohistochemistry in all cases. The affected cats were five castrated males and three spayed females. Domestic Shorthair cats were affected more often (seven cases), with one affected Domestic Mediumhair cat. The age of patients ranged from 6 months to 10 years (median age = 8.5 years). Clinical signs consisted of ulcerative and crusting lesions that affected sites including the nose (six cases), right flank (one case) and right elbow, right shoulder and tarsal area (one case). Histological changes were typical of FeAHV1 infection in all cases and included epidermal necrosis that extended to the hair follicle, ulceration and serocellular crusts, with intranuclear eosinophilic viral inclusions within epithelial cells of the epidermis, hair follicle and sebocytes. Intranuclear viral inclusions within macrophages were observed in two cases. The dermis was infiltrated by eosinophils admixed with neutrophils, macrophages, lymphocytes and plasma cells. Transmural vascular changes consisting of mixed inflammatory cell infiltrates, fibrinoid change and thrombosis were present in small- to medium-sized arterioles and venules in the dermis in six cases. In two cases, these vascular changes were associated with perivascular dermal necrosis and haemorrhage. Although not previously reported in detail, inflammatory -vascular changes occur in cases of FeAHV1 dermatitis and may be secondary to extensive epidermal necrosis and ulceration.