The First Report of Equine Cutaneous Protothecosis

Introduction
Prototheca species are ubiquitous, achlorophyllous unicellular algae. they have been found in water, sewage, slime flux of trees and soil and reportedly cause a rare mycosis- like systemic or local disease in a wide variety of mammals including humans, dogs, cats, pigs and cattle. protothecosis has been reported to occur associated with condi- tions that cause immunosuppression.

Material and Methods
In this report, a case of equine cutaneous protothecosis diagnosed histopathologically was described. a 10-year-old turkmen horse was referred with multiple verrucous, ulcerated lesions up to 1.5 cm in diameter on the left external ear (pinna). the horse was vigorous and had a normal appetite and good body condition. a biopsy of the mass was procured and tissue sections stained with H&E, paS and GMS. also fungal culture of lesion material was carried out on SDa at 28°C & 37°C.

Results
Ten to fifteen μm, ovoid to reniform, pale basophilic organisms, each 2 to 3 μm diame- ter, were observed within the epidermis and keratin layer. the organisms were tenta- tively identified as prototheca species by histopathological feature. the sporangia con- taining endospores by paS and morulae–like internal septation among the necrotic material were observed. Histopathologically, moderate acanthosis of epidermis and a chronic severe granulomatous dermatitis was diagnosed. the organisms mentioned above were noted within giant cells in the superficial dermis. after incubation for 4 days on sabouraud’s dextrose agar, smooth creamy white moist colonies were obtained and were identified as prototheca species by assimilation test using rapidiD yeast plus test.

Conclusion
Finally, histopathologic examination & fungal culture confirmed cutaneous protothecosis. this seems to be the first report of cutaneous protothecosis in a horse.