Subcutaneous Mycoses

By | November 15, 2015
  • infection by fungi of viable skin, often traumatically induced
  • very rare in the UK
  • examples include eumycotic mycetoma, phaeohyphomycosis, pythiosis, protothecosis and sporotrichosis
  • identification of these fungi should be undertaken only by an experienced veterinary mycologist

Eumycotic mycetoma

  • rare in dogs and cats
  • trauma-induced, may involve the skin, subcutaneous tissue, fascia and bone
  • causal fungi include Allescheria boydii and Curvularia geniculata
  • causal actinomycetes include Actinomyces and Nocardia

Clinical features

  • frequently there is a triad of swelling, draining fistulae and granules
  • usually localized lesion, typically on a foot
  • may be painful and swollen

Diagnosis

  • culture on plain Sabouraud’s agar
  • histopathology: demonstration of fungal elements with specialized stains such as PAS

Differential diagnosis

  • abscesses
  • foreign body reactions
  • neoplasms

Treatment

  • radical surgical excision
  • there is no effective medical therapy

Phaeohyphomycosis

  • mainly cats, a few cases have been reported in dogs
  • rare
  • causal fungi in cats include Drechslera spicifera, Phialophora verrucosa, Moniella suaveloens and Exophiala jeanselmii
  • causal fungi in dogs include D. spicifera, Phialemonium obovatum and Pseudomichrodochium suttonii

Clinical features

  • early lesions are painless subcutaneous nodules
  • later, fistulation occurs with a purulent exudate
  • ulceration may occur
  • lesions tend to form on the distal extremities and trunk

Diagnosis

  • culture on plain Sabouraud’s agar

Differential diagnosis

  • chronic abscessation
  • foreign-body reaction
  • feline leprosy
  • eumycotic mycetoma

Treatment

  • surgical excision
  • amphotericin B or ketoconazole may be tried

Pythiosis (Phycomycosis)

  • rare
  • dogs
  • warm climates only, e.g. south-eastern United States
  • usually seen in dogs that have access to stagnant water
  • caused by fungi of the genus Pythium (often pathogens of aquatic plants)

Clinical features

  • ulcerated nodules on the limbs, posterior dorsum and tail or face
  • may develop fistulae with a serosanguinous or purulent exudate

Diagnosis

  • culture from material collected surgically from the centre of lesions

Differential diagnosis

  • other fungal infections
  • deep pyoderma
  • demodicosis
  • acral pruritic granuloma
  • neoplasms

Treatment

  • radical surgical excision of the lesion (amputation of affected portion of a limb may be necessary)
  • antifungal medical therapy is ineffective

Protothecosis

  • rare
  • dogs and cats
  • causal agents are achlorophyllous algae related to the green algae Chlorella spp.
  • Prototheca urickerhamii is the only species to have been recovered from dogs and cats
  • there has been a report of this condition in the UK in a 10-year-old greyhound ()

Clinical features

  • small nodules which may ulcerate and discharge a thick exudate
  • these nodules may occur on the limbs, nose, chest and head
  • may spread to the regional lymph nodes

Diagnosis

  • culture on plain Sabouraud’s agar
  • biopsy and stain with PAS

Differential diagnosis

  • deep pyoderma
  • fungal infections
  • neoplasms
  • atypical mycobacterial infections
  • systemic mycoses with skin manifestations

Treatment

  • surgical removal of nodules in early stages
  • ketoconazole may be tried but the condition is usually refractory to treatment

Sporotrichosis

  • rare
  • dogs and cats
  • warm climates only
  • public health risk
  • causal fungus is Sporolhrix schenkii
  • there are three clinical syndromes:
  • cutaneolymphatic: nodules on the skin of the extremities, infection spreading to the regional lymph nodes; the nodules rupture with a red-brown discharge
  • cutaneous: circumscribed, alopecic, plaque-like non-painful lesions
  • disseminated: invasion of many tissues

Diagnosis

  • culture on Sabouraud’s dextrose agar
  • biopsy

Differential diagnosis

  • chronic ulcerative conditions
  • granulomas
  • other mycoses
  • feline leprosy
  • deep pyoderma

Treatment

  • the cutaneous and cutaneolymphatic forms respond well to inorganic iodide therapy

Dogs: 0.2 mg/kg of a 20% solution of sodium iodide is given orally b.i.d. for four weeks beyond clinical remission; at this dose (40 mg/kg) improvement should be noticed within a week

Cats: A lower dose (20 mg/kg) is recommended, since cats are more susceptible to iodinism; toxic signs in the dog include vomiting, depression and seborrhoea sicca; in the cat there may be vomiting, depression, anorexia and cardiac depression

 

Selections from the book: “Skin Diseases in the Dog and Cat”. D. I. Grant, BVetMed (1991)