Treponema spp. spirochetes and keratinopathogenic fungi isolated from keratomas in donkeys

Keratoma is an aberrant keratin mass thought to originate from epidermal horn-producing cells interposed between the stratum medium of the hoof wall and the underlying third phalanx. The cause is unknown, although the presence of keratomas is frequently associated with chronic irritation, focal infection, or trauma. A total of 167 donkeys with keratomas were presented in this study. Diagnosis of a keratoma was based on clinical signs, radiography, and histopathologic examination. Surgical excision was attempted on all donkeys with lameness unless euthanasia was advised. Histopathologic examination, including Giemsa, periodic acid Schiff (PAS) and Young’s silver special histochemical stains were performed and showed the presence of fungal hyphae and spirochete bacteria within the degenerate keratin. PCR for treponeme bacteria was performed on 10 keratoma lesions and 9 healthy pieces of hoof (controls). All healthy donkey tissues were negative for the three recognised digital dermatitis (DD) treponeme phylogroups whereas 3/10 (30%) of donkey keratoma samples were positive for one of the DD treponeme phylogroups. Routine fungal culture and PCR for fungi was performed on 8 keratoma lesions and 8 healthy pieces of hoof (controls). Keratinopathogenic fungi were detected in 1/8 (12.5%) keratomas while only non-keratinopathogenic, environmental fungi were detected in 8 control healthy hoof samples. This is the first time DD treponemes phylogroup and keratinopathogenic fungi have been detected in keratomas. Further studies are required to assess the significance of this finding.