Dermatophytosis
Basic Information 
Clinical Presentation
History, Chief Complaint
Presence of multiple circular alopecic lesions, mostly on the face, legs, girth, shoulder, and chest
Physical Exam Findings
• The classic appearance in horses is a ring lesion with the central area often showing signs of healing. Scaling and crusting of these lesions can be variable, and pruritus is minimal or absent and may become exudative. The lesions may expand and start coalescing, creating large patches of alopecia. Some of these lesions may show a silver tinge to them, hyperpigmentation, and lichenification.
• Multiple lesions are typically present, but solitary lesions may rarely be present.
• Immunocompromised foals or horses may be severely affected and may develop generalized dermatophytosis.
Etiology and Pathophysiology
• Trichophyton equinum, Microsporum equinum, Trichophyton mentagrophytes, and Trichophyton verrucosum infection
• Direct or indirect transmission may occur. Contaminated grooming equipment, blankets, and tack may be a source of transmission, as can insects.
• Stress or concurrent disease may predispose horses to development of dermatophytosis.
• The incubation period is between 2 and 3 weeks. During this period, other horses very likely are already infected and starting to show signs of disease.
• Dermatophytes only invade fully keratinized and nonliving tissues, which leads to weak hair shafts and alopecia.
• Superficial infections are the most common and develop thick crusts and a classic moth-eaten appearance and a ring pattern.
• Erythema is not usually seen and can be difficult to identify in pigmented skin.
• Most infections are self-limiting over a 5- to 10-week period, but treatment is recommended to limit the spread of infection.
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