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Skin: blastomycosis

pequis

Introduction

  • Cause: uncommon form of a rare disease caused by infection byBlastomyces dermatitidis  Blastomyces dermatitidis  . Infection within the skin probably follows trauma in the primary form, but may be part of a multisystemic involvement.
  • Signs: multiple firm skin nodules resembling exuberant granulation tissue with serosangineous exudation and crusting. Some of the nodules may be subcutaneous with normal haired skin, up to 3 cm diameter. The lesions may be painful on palpation.
  • Diagnosis: clinical signs, cytology, skin biopsy with histopathology and cultures. Serology and PCR used in other species.
  • Treatment: amphotericin B and long-term potassium iodide or oral azole drugs such as ketoconazole, itraconazole and fluconazole have been used in humans, small animals and rare equine cases. Voriconazole has been used in refractory systemic human cases. Surgical removal of nodular subcutaneous lesions.
  • Prognosis: good to poor with high incidence of recurrence and the need for long-term, expensive therapy.

Pathogenesis

Etiology

  • Blastomycosis is a systemic fungal disease that is reported in man and less frequently in dogs and cats. It is very rare in the horse (systemic blastomycosis) and rarely presents in the cutaneous form.
  • The causative organism isBlastomyces dermatitidiswhich is a thermally dimorphic saprophytic fungus that is present in the environment as a mould.
  • The organism can infect the body as conidia via inhalation or direct inoculation into the skin.

Predisposing factors

General
  • Presence of organism in the environment.

Specific

  • Traumatic injury of the skin followed by direct inoculation of the fungus is the most likely route of skin blastomycosis infection in the horse.

Pathophysiology

  • Blastomyces dermatitidiscauses disease in man, dog, cats and horses (in order of frequency).
  • Disease most commonly affects the lungs, skeletal bones, genitourinary tract and the central nervous system.
  • Primary pulmonary lesions following inhalation of the fungus are the most common but there may be involvement of many other tissues, probably via hematogenous spread around the body.
  • Cutaneous lesions are the most common extra-pulmonary manifestation in the other species.
  • Primary skin lesions in all species are rare, probably due to direct traumatic inoculation of the fungus.
  • Injured skin can become contaminated with infective material.

Timecourse

  • The median incubation period for the cutaneous form is approximately 2 weeks, which is shorter than for pulmonary-derived infections.

Epidemiology

  • Endemic in some parts of North America and present also in Africa and India; is also being reported in Europe as well.
  • People with work-related exposure (mycology laboratory personnel, veterinarians) and outdoor activities in endemic areas are at higher risk.
  • Rarely transmitted from animals to man; during man and dog outbreaks a common source of infection was likely rather than direct transmission.
  • Transmission from person to person is unlikely.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Funiciello B et al (2014) Cutaneous blastomycosis in a horse. Equine Vet Educ 26 (9), 458-463 VetMedResource.
  • Méndez-Angulo J L et al (2011) Blastomycotic osteomyelitis associated with severe lameness in a horse. Can Vet J 52 (12), 1303-1307 PubMed.
  • Saccente M & Woods G L (2010) Clinical and laboratory update on blastomycosis. Clin Microbiol Rev 23 (2), 367-381 PubMed.
  • Schwarz B et al (2009) Cutaneous fungal granuloma in a horse. Vet Dermatol 20 (2), 131-134 PubMed.
  • Wilson J H et al (2006) Systemic blastomycosis in a horse. J Vet Diagn Invest 18 (6), 615-619 PubMed.
  • Dolente B A et al (2003) Disseminated blastomycosis in a miniature horse. Equine Vet Educ 15 (3), 139-142 VetMedResource.
  • Toribio R E et al (1999) Thoracic and abdominal blastomycosis in a horse. JAVMA 214 (9), 1357-1360 PubMed.

Other sources of information

  • Scott D W & Miller W H Jr (2011) Fungal Skin diseases. In: Equine Dermatology. 2nd edn. Saunders, USA. pp 171-211.
  • Knottenbelt D C (2009a) Syndromes in Equine Dermatology. In: Pascoes Principles and Practice of Equine Dermatology. 2nd edn. Ed: Knottenbelt D C. Saunders, St. USA. pp 441-485.
  • Knottenbelt D C (2009b) Fungal diseases. In: Pascoes Principles and Practice of Equine Dermatology. 2nd edn. Ed: Knottenbelt D C. Saunders, USA. pp 167-185.

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