Subcutaneous and Deep Mycoses

Subcutaneous/Deep Mycoses

• Involve subcutaneous tissues in addition to dermal/epidermal involvement
• Can be localized or spread insidiously to contiguous tissues and via lymphatic vessels
• Difficult to diagnose and treat, with seroconversion leading to chronic and progressive disease
• More serious but geographically restricted, and rare or very rare in horses

Trichophytosis

• Caused by Trichophyton spp.
• Very common cutaneous mycosis worldwide
• Spores highly resistant, leading to repeated infections in stables/yards
• Requires epidermal damage to gain entry and remain in follicles of hair shafts
• Site of infection typically areas of superficial skin trauma (tack and harness contact points)

Clinical Signs of Trichophytosis

• Early signs: erect hairs, local swelling/edema, and mild exudate
• Advanced signs: complete shedding of hairs, lesions easily and completely epilated, leaving silvery exposed epidermis
• Common sites of infection: abrasions of rider's boots and girths

Diagnosis and Treatment of Trichophytosis

• Diagnosis: clinical signs, differential diagnosis with other fungal diseases, and biopsy
• Treatment: isolation of infected horse, hygiene and sanitation, topical antifungal washes, oral griseofulvin (not for pregnant mares), and use of fungicidal disinfectants

Control of Trichophytosis

• Vaccination in some countries
• Early recognition and isolation of infected horses
• Stable and personal hygiene
• Individualized tack, harness, and rugs
• Use of gloves

Microsporosis

• Caused by Microsporum spp.
• Less common than Trichophyton spp. infections
• Isolated lesions more common than extensive coalescing areas
• Pathogenesis same as trichophytosis
• Common species: M. equinum, M. canis, M. gypseum

Clinical Signs of Microsporosis

• Early signs: small expanding areas of localized edema resembling urticaria
• Advanced signs: early lesions with exudate and mildly pruritic, horse rubs affected areas but does not bite
• Plucking of hairs resented because not all hairs are affected

Diagnosis and Treatment of Microsporosis

• Diagnosis: clinical signs, cultures and microscopy of stained smears and hairs, and secondary urticarial-like plaques
• Treatment: local topical washes with fungicide, environmental disinfection, and sunshine (strong inhibitor of Microsporum spp.)
• Prognosis: excellent, most resolved spontaneously within 6-12 weeks

Aspergillosis (Guttural Pouch Mycosis)

• Fungal infection caused by Aspergillus species
• Primarily a respiratory infection that may become generalized
• Found worldwide in almost all domestic animals and many wild animals
• Susceptibility to fungal infections varies among species
• Most common form in horses: fungal disease affecting the guttural pouch

Clinical Signs of Aspergillosis

• Nosebleed and difficulty in breathing or swallowing
• Holding the head extended or low, head-shaking, swelling of the head, neurologic signs, and nasal discharge

Treatment of Aspergillosis

• Topical and oral antifungal agents
• Outlook: guarded, horses may survive but not recover completely, particularly if nerves are damaged

Candidiasis

• Localized fungal disease affecting mucous membranes and skin
• Caused by Candida albicans
• Distributed worldwide in various animals
• Most commonly seen in foals
• Signs: variable and nonspecific, may be associated with primary or predisposing conditions

Treatment of Candidiasis

• Ointment or topical application
• Different drugs given by mouth or through the vein to resolve arthritis or treat generalized candidiasis

Coccidioidomycosis (Valley Fever)

• Dustborne, noncontagious infection caused by Coccidioides immitis
• Limited to dry, desert-like regions of the southwestern United States and similar areas of Mexico and Central and South America
• Inhalation of fungal spores is the only established mode of infection
• Epidemics may occur when rainy periods are followed by drought, resulting in dust storms

Clinical Signs of Coccidioidomycosis

• Loss of weight, coughing, fever, musculoskeletal pain, and abscesses of the skin
• Nodules develop under the skin, increasing in size and undergoing cycles of granulation and partial healing

Diagnosis and Treatment of Coccidioidomycosis

• Diagnosis: microscopic examination of discharges from infected area or biopsy specimens
• Treatment: surgical removal of lesions combined with antifungal drugs, but no completely satisfactory treatment is known
• Strict hygienic precautions are essential to prevent spread

Pythiosis

• Disease caused by Pythium insidiosum, a water mold
• Occurs in tropical and subtropical areas of the world, seen in warmer sections of the US
• Infections in horses are most commonly restricted to the skin and tissues just inside the skin
• Large, circular nodules or areas of swelling can become open, draining sores

Treatment of Pythiosis

• Antifungal drugs may be considered in cases when surgery is not possible
• Antifungal treatment is long-term (6-12 months), expensive, and has variable results

Rhinosporidiosis

• Chronic infection, primarily of the lining of the nasal passages and occasionally of the skin
• Caused by Rhinosporidium seeberi
• Rarely fatal, and uncommon in North America
• Seen most often in India, Africa, and South America

Clinical Signs of Rhinosporidiosis

• Nasal discharge and sneezing
• Infection of the nasal mucosa is characterized by polyp-like growths
• Skin lesions may be single or multiple, attached at a base or have a stem-like connection

Treatment of Rhinosporidiosis

• Surgical removal of lesions is considered the standard treatment, but recurrence is common

Sporotrichosis

• Sporadic chronic disease caused by Sporothrix schenckii
• Organism is found around the world in soil, vegetation, and timber
• Infection usually results when the organism enters the body through skin wounds
• Transmission of the disease from animals to humans can occur

Clinical Signs of Sporotrichosis

• Small, firm nodules develop at the site where infection enters the body
• Although generalized illness is not seen initially, chronic illness may result in fever, listlessness, and depression