Cutaneous cryptococcosis in a Haflinger horse

Background: Cryptococcosis is caused by yeast-like fungi, which belong to the Cryptococcus gattii/ Cryptococcus neoformans species complex. Equine cryptococcosis is uncommon, it mainly affects the respiratory system and rarely disseminates to the skin through the hematogenous route. Objectives: Report the main clinical and pathological features of skin lesions caused by Cryptococcus spp. in a horse. Methods: A 9-year-old Haflinger mare developed multiple skin lesions during the last 4 years. Lesions were 1-to-5 cm in size and mostly affected the groin, the pectoral region and the neck. Some lesions were bulging, arranged as clusters, hyperemic, ulcerated, while others were flattened and crusty. The mare was otherwise healthy and showed an optimal body condition score, the hematobiochemical parameters being within the normal range of values. Considering clinical findings, equine sarcoid was suspected, a couple of large lesions were surgically removed for histopathological investigation and to prepare the autologous vaccine. Results: Microscopically, a huge number of round or oval microorganisms were seen, 5-10 m in diameter and typically surrounded by a clear halo. Such microorganisms were arranged as aggregates, thus shaping a characteristic bubble-like appearance, and proved to be positive for Grocott methenamine silver stain. Moreover, granulomatous reactions with multinucleated giant cells and foci of purulent inflammation were seen. Considering clinical, pathological and biomolecular findings, cutaneous cryptococcosis was diagnosed. The mare is still alive, dozens of skin lesions being still present. Conclusions: This is among the few reports of equine cutaneous cryptococcosis, without any apparent involvement of internal organs, and it highlights that cryptococcosis should be considered in differential diagnosis of neoplastic-like skin lesions in horses.