Molecular identification of Phialophora oxyspora as the cause of mycetoma in a horse.
METHODS
An 18-year-old mare was evaluated for an oral mass that developed after extraction of a broken incisor.


RESULTS
An ulcerated, firm, darkly pigmented, approximately 5-cm-diameter spherical mass involved the gingiva lateral and dorsal to the right first to third maxillary incisors. Osteolysis of the roots of the first and second right maxillary incisors and periosteal proliferation of the adjacent premaxilla margins were apparent on radiographs. Histologic examination of the mass revealed multiple coalescing and ramifying foci of abscess formation, each containing a well-defined, discrete, black mass (2 to 7 mm in diameter). Myriad fungal hyphae enmeshed in a black, granular, cementlike material were within each of the black structures. Mycetoma was the histologic diagnosis. The causative agent could not be identified via culture because of lack of distinguishing characteristics. Fungal DNA was isolated from frozen fungal cultures and paraffin sections. The D1/D2 domains of the large subunit P gene rDNA were amplified and sequenced. The sequences of the D1/D2 domains of both isolates were 96% homologous with those of Phialophora oxyspora.


RESULTS
The mass was surgically excised, the local area curetted, and the wound allowed to heal by second intention. Postoperative treatment consisted of administration of phenylbutazone and IV administration of sodium iodide followed by oral administration of potassium iodide. There was no evidence of recurrence 1 year later.


CONCLUSIONS
Mycetomata should be a differential diagnosis for equine gingival masses. Identification of the fungal agent can be critical for selection of optimal treatments. Molecular methods may permit definitive identification when standard phenotypic-based identification criteria are inconclusive.
Lopez
Mandi J
MJ
Laboratory for Equine and Comparative Orthopedic Research, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803, USA.
Robinson
Sandra O
SO
Cooley
A James
AJ
Prichard
Michael A
MA
McGinnis
Michael R
MR
D000818:Animals; D000935:Antifungal Agents / Q000627:therapeutic use*; D003646:Debridement / Q000662:veterinary; D005260:Female; D006734:Horse Diseases / Q000175:diagnosis* / Q000188:drug therapy / Q000601:surgery; D006736:Horses; D008271:Mycetoma / Q000175:diagnosis / Q000188:drug therapy / Q000601:surgery / Q000662:veterinary*; D009181:Mycoses / Q000175:diagnosis / Q000188:drug therapy / Q000601:surgery / Q000662:veterinary*; D010676:Phialophora / Q000254:growth & development / Q000302:isolation & purification*; D011183:Postoperative Complications / Q000662:veterinary; D014081:Tooth Extraction / Q000009:adverse effects / Q000662:veterinary; D016896:Treatment Outcome
D000935:Antifungal Agents