Subcutaneous Mycoses

FUNGI

Chromomycosis

• Also called Phaeohyphomycosis

• Opportunistic

• Infects horses, dogs and humans
  • Found in wounds and abrasions

• Caused by dematiaceous fungi
  • Dactylaria gallopava, Exophiala pisciphila, E. salmonis, Scolecobasidium humicola, S. tshawytschae, Drechslera, Exophilia jeanselmeri, E. verrucosa, Fonsecaea pelrosoi

• Nodular and ulcerating lesions of the skin on the feet, legs and occasionally eyes (in turkeys)
  • Regional granulomatous lymphadenitis

• Single cells or clusters, spherical and thick-walled
• Brown pigmented fungal elements

• Multiply by cross-wall formation or splitting (not budding)

• Grows on Sabauraud's Dextrose agar ar room temperature
  • Slow growth
  • Takes one month

• For further information, see dematiaceous fungi

Eumycotic Mycetoma

• Pseudoallescheria boydii, Curvularia geniculata, Cochliobolus spicifer, Helminthosporium spp.

• Lives in soil

• Enters the body via wounds

• Granulomatous abscesses

• Microcolonies can be seen grossly in exudate or lesions
  • Grains or granules
  • Brown or black embedded in granulation tissue
  • Small, irregularly shaped

• Infrequent infections of dogs, cats, cattle and horses

• Usually affect the extremities
  • Can infect the nasal mucosa
    • E.g. Bovine nasal granuloma
  • Can also infect the peritoneum and skin

• Microscopically:
  • Grains of maduromycosis with wide mycelia (compared to actinomycotic granules)
  • Chlamydospores present

• Grows on Sabauraud's Dextrose agar
  • Slow
  • Takes 2-3 weeks

• Treatment includes Ketoconazole, 5-fluorocytosine and amphotericin B

Pythiosis

• Causes Mycotic Swamp Fever

• Also called phycomycosis

• Occurs in the USA, Australia, New Guinea, India, Brazil, Colombia, Japan, Costa Rica and Indonesia

• Pythium insidiosum

• Enters via wounds
  • Lips, head, neck, fetlock, hock and hoof

• Granulomatous infection
  • Necrosis and fistulous tracts
  • Yellow lesions

• Branching, separated fungi

• Progressive (rather than systemic) disease

• Surgery is needed

Sporotrichosis

• Sporothrix schenckii

• Occurs in soil, wood and vegetation

• Worldwide

• Exogenous infections through wounds

• Causes subcutaneous nodules or granulomas
  • Nodules ulcerate discharging pus

• Spread via the lymphatics

• The bones and viscera can be involved which terminates in mortality
  • This is rare
  • Reported in dogs and horses

• Affects dogs, horses, cats, monkeys, mules, camels, donkeys, cattle, fowl and rodents
  • Most commonly seen in horses as an ascending lymphocutaneous infection of the legs

• Single cell, cigar shaped
  • Usually found within neutrophils
  • Yeast cell clusters with peripheral eosinophilic rays can be seen in tissue sections

• Stained using PAS, fluorescent antibody and Calcofluor White

• Latex agglutination and immunodiffusion serology can be performed

• Grows on Blood agar and Sabouraud's Dextrose agar in one to three weeks
  • At 37°C:
    • Colonies are smooth, cream to tan coloured and soft
    • No mycelium can be seen
  • At 25°C to 27°C:
    • Colonies turn from white and soft to tan to brown to black
    • Leathery, wrinkled and coarse
    • Mycelium can be seen as branching septate hyphae
    • Conidiospores can also be seen

• Potassium iodide treatment orally
  • 5-fluorocytosine and amphotericin B can also be used

Further Links

• Pathology of subcutaneous mycoses

• Antifungal Drugs