Equine Mycotic Diseases

Equine Mycotic Diseases

• Opportunistic fungi commonly affect immunocompromised hosts
• Predominant sites of infection: skin, respiratory tract, and guttural pouches
• Guttural pouch mycosis can lead to fatal haemorrhage
• Dermatophytes isolated from animals, zoophilic species responsible for most cases: Microsporum canis, Trichophyton mentagrophytes, Trichophyton equinum, Trichophyton verrucosum, and Microsporum gypseum
• T.equinum is the most prevalent dermatophyte
• Equine dermatophytosis is also known as "ringworm" and has public health significance

Aspergillosis (Guttural Pouch Mycosis)

• A fungal infection caused by several Aspergillus species
• Primarily a respiratory infection, but can become generalized
• Found worldwide in domestic and wild animals but susceptibility varies
• Aspergillus fumigatus is responsible for increased invasive aspergillosis in immunocompromised individuals
• A. fumigatus is the dominant organism in guttural pouches, along with A. versicolor, A. nidulans, and A. niger

Epidemiology

• Emericella nidulans from bedding materials has also been associated with guttural pouch mycosis

Pathophysiology

• Invasive mycoses are difficult to diagnose and treat
• Many fungal pathogens are opportunistic, primarily infecting immunocompromised hosts
• Mycotic lesions observed in normal horses within 2-4 days after inoculation with A. fumigatus followed by corticosteroid administration
• Spontaneous regression observed within 15-28 days in the experimental infection model

Clinical Presentation

• Common signs of guttural pouch mycosis include epistaxis, nasal catarrh, pharyngeal paralysis, laryngeal hemiplegia, submandibular/parotid swelling, head and neck extension, and dyspnea
• Cases with pharyngeal paralysis are typically fatal

Differential Diagnosis

• Horses with gastrointestinal diseases and unresponsive respiratory tract infections may be at risk for pulmonary aspergillosis
• Other causes of epistaxis without fever include trauma and progressive ethmoidal hematoma

Diagnosis

• Diagnosis relies on clinical presentation, antigen detection, and molecular assays
• Isolation and identification of the fungus determines antifungal drug susceptibility
• A pan-dermatophyte PCR assay targets the translation elongation factor for detection of relevant dermatophytes
• Real-time PCR, MALDI-TOFMS, and nano-ESI-MS can also be used to diagnose mycotic infections
• Guttural pouch mycosis can be visualized via endoscopy

Pathology

• Microscopic examination confirms intralesional fungal organisms
• Fungi present as septate hyphae with dichotomous branching and conidia

Treatment

• Treatment typically involves surgery or medical management
• Antifungal therapy is essential and should be tailored to the specific fungal species
• Surgical approaches may be necessary for cases with significant tissue damage
• Prognosis depends on the severity of the infection and the overall health of the horse