Phaeohyphomycosis

From Dog

Phaeohyphomycosis (chromoblastosis, or eumycotic mycetoma) is a mycotic infection of dogs caused by a number of dematiaceous (brown-pigmented) fungi where the tissue morphology of the causative organism is mycelial. This separates it from other clinical types of disease such as ringworm which involves microcidial infections[1].

Dematiaceous fungi are widespread in the environment and are found in soil, wood and decomposing plant debris. Some of the organisms in this group have been isolated in culture studies of the pelage and mucosal surfaces of dogs with and without clinical signs of cutaneous fungal disease.

Dematiaceous fungi usually are inoculated into the host by direct trauma from a wood splinter, via bite wounds, or by contamination of an existing open wound. Most infections with dematiaceous fungi cause subcutaneous nodules and/or tracts that contain purulent exudates. Fever and other systemic signs are usually absent.

Cytological examination of exudates usually reveal pyogranulomatous inflammation that may contain fungal hyphae. Fungal culture is usually recommended to diagnose this disease.

Complete surgical excision of the affected tissue is the treatment of choice and is the treatment most likely to eliminate infection successfully. Unfortunately, definitive diagnosis is often delayed because of the unusual nature of the infection, and often extensive tissue involvement precludes complete excision and medical adjunct therapy is initiated.

Medical therapy is often guarded due to the slow-growing nature of fungi and resistance to most medications. Itraconazole is currently the drug of choice and has been used successfully to clear infection in some patients[2]. Combination therapy with terbinafine and an azole anti-fungal drug appears to be effective in dogs.

Pathogenic fungi that cause phaeohyphomycosis include:

Alternaria spp Paecilomyces spp
Aureobasidium spp Phialosimplex caninus
Bipolaris (Dreshlera) spp Phialemonium curvatum
Cladophialophora bantiana Pseudallescheria boydii
Cladosporium spp Ramichloridium mackenziei
Curvularia spp Sagenomella chlamydospora
Dactylaria spp Scedosporium spp
Exophiala spp Scolecobasidium humicola
Exserohilum spp Scytalidium dimidiatum
Fonsecea pedrosoi Staphylotrichum coccosporum
Madurella spp Stemphylium spp
Microsphaeropsis spp Wangiella dermatidis
Moniliella suaveolens Xylohypha bantiana
Ochroconis gallopavum

References

  1. Brandt, ME & Wanock, DW (2003) Epidemiology, clinical manifestations and therapy of infections caused by dematiaceous fungi. J Chemother 15 (supp):36-47
  2. Rochette, F Englen, M & van den Bossche, H (2003) Anti-fungal agents of use in animal health-practical applications. J Vet Pharmacol Therapy 26:31-53