Subcutaneous Mycoses

FUNGI

Chromoblastomycosis

Chromomycosis

Epizootic Lymphangitis

• Histoplasma capsulatum var. farciminosum
  • Similar to H. capsulatum

• Occurs in horses, donkeys and mules
• 90% occurs in horses

• Occurs in Europe, Africa and Asia
  • Eradicated from the UK but is still under the notifiable Diseases of Animals Act

• Chronic disease

• Highly contageous
  • Spread by direct contact or indirect, e.g. through infected grooming equipment, biting flies

• Once established in a population it is very difficult to eradicate
  • Long incubation peroid
  • New cases can develop weeks or months after the infection appears to have been eradicated

• Affects the lymph nodes, lymph vessels and skin
  • Mostly of the neck and limbs

• Causes ulcerative, nodular lesions
  • Dissemination occurs
  • Pulmonary disease can occur
  • Ulcers rupture, discharging blood-stained pus for several weeks

• Oval or pear shaped cells
  • Double contoured
  • Dimorphic
    • Grows in the yeast phase at 37°C and in the mycelial phase at room temperature
  • Growth is slow, taking up to 8 weeks
  • At room temperature, thick-walled chlamydospores can be seen
  • Orgnaisms can usually be seen in swollen leucocytes

• Can be stained using Gram, Giemsa, H & E and 10% Methylene Blue followed by Carbol Fuchsin

• Enzyme-linked immunosorbant assay can be used to detect the fungi

• Life-long immunity follows recovery from infection

• Treatment included potassium iodide, hamycin and Amphotericin B
  • Vaccination has also proven to be effective
  • Injection of hyperimmune serum around skin lesions has been proven to be effective

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

Hyphomycosis

• Hyphomyces destruens

• Opportunistic infection
  • Associated with trauma

• Rare

• Caused by Penicillium, Beauveria, Acremonium, Fusarium, Paecilomyces

• Infects both animals and humans
  • Mainly affects horses

• Tropical and semi-tropical countries

• Progressive disease causing granulating and ulcerating lesions on the legs and lower body
  • Lesions grow rapidly
  • Cause extreme debility

• Occurs in water
  • Most often seen in ponies with access to ponds

• Chemotactically attracted to horse hair

• Does not respond well to treatment
  • Radical surgical excision the best method
  • Experiemental vaccination treatment is currently underway and has shown promising results

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

Rhinosporidiosis

• Rhinosporidium seeberi

• Lives in water

• Causes a chronic, benign disease

• Affects cattle, mules, horses, dogs and humans

• Causes polyps on the nasal and ocular mucous membranes
  • Over 90% of cases affecting the nasal mucous membranes affects male animals

• Occurs most frequently in tropical countries
  • Also common in the USA

• Large sporangia can be seen on wet mounts
  • Endospores visible
  • Sporangia develop into small, globose spores

• Treatment is by surgical excision

Sporotrichosis

Sporotrichosis in a horse -Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath

Sporotrichosis cigar shaped cells -Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath

• Sporothrix schenckii

• Occurs in soil, wood and vegetation
  • Saprophyte of both decaying and healthy vegetation

• Worldwide

• Exogenous infections through wounds

• Sporadic infections

• Non-contageous

• 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
  • Can be confused with epizootic lymphangitis in horses

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

• Stained using PAS, Gram stain (positive), 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