Introduction: A 3-year-old castrated male donkey was presented with multifocal, moderately firm, dull, white nodules, varying in size from 0.5-2.0 cm in diameter. The nodules were located on the skin of the penile shaft and showed depigmentation. Other locations on the body were not involved.
Materials and Methods: Surgical excision of the nodules was performed. All formalin-fixed samples were embedded in paraffin and routinely processed for histopathological examination.
Results: Histopathological examination revealed presence of multifocal, round to oval, protozoal cysts within the dermis, with a size of 150-500 μm. The mature cyst walls consisted of four distinct layers, including an outer, hyalinized, eosinophilic layer of collagen fibers, a thin homogenous intermediate layer, a layer consisting of the cytoplasm of the host fibroblast with a compressed nucleus, and an inner layer that formed the parasitophorous vacuole. The vacuole was filled with numerous bradyzoites of 2 x 8 μm. There was a mild to moderate, superficial to mid-dermal infiltration of lymphocytes, plasma cells, macrophages and eosinophils, surrounding the cysts and blood vessels. The hair follicles were atrophic. The overlying epidermis showed mild acanthosis and orthokeratotic hyperkeratosis. Based on the histopathological findings, a diagnosis of Besnoitia sp. infection was made.
Conclusions: Besnoitiosis is an emerging disease in cattle in Europe. Few outbreaks have been reported in donkeys in the USA. To our knowledge, this is the first report in the literature of Besnoitia sp. infection in an European donkey.