ISSN 2398-2985      

Blastomycosis

4ferrets
Contributor(s):

Joanne Sheen

Kim Le

Synonym(s): Blastomyces dematitidis


Introduction

  • Cause: a thermally dimorphic fungus, Blastomyces spp.
  • Signs: can be highly variable depending on organ and body system(s) affected. Anorexia, lethargy, coughing, sneezing, dyspnea, lymphadenopathy, ulcerated skin lesions, ataxia, paresis, weakness, altered mentation.
  • Diagnosis: detection of Blastomyces elements within tissue or fluid samples. Typically, antigen testing of serum or urine, or through PCR testing on tissue samples.
  • Treatment: supportive care together with prolonged treatment with antifungal agents.
  • Prognosis: traditionally thought to be guarded to poor. May be fair with appropriate antifungal therapeutic regime and extensive regular diagnostic testing and monitoring.

Pathogenesis

Etiology

  • Blastomyces spp is a thermally dimorphic fungi that is endemic in much of eastern North America.
  • The organism is typically found in moist, acidic, sandy soil, with frequent proximity to a water source such as lakes and rivers, although wind may also contribute to its dispersal.
  • Blastomyces spp grows as mold in soil at temperatures <30°C/86°F (saprophytic stage) and as a yeast in tissues at temperatures >33°C/91.4°F (parasitic stage).
  • B. dematitidis is the most commonly reported etiologic agent.
  • Other species such as B. helices and B. percursus have also been recently recognized to be involved in human blastomycosis in North America and Africa.

Predisposing factors

General

  • Exposure to Blastomyces spp endemic environments.

Specific

  • Immunocompromise, specifically impaired cell-mediated immune response.

Pathophysiology

  • Blastomyces spp inhabiting soil produce infectious conidia (spores).
  • Disruption of soil allows Blastomyces mold and conidia to become aerosolized.
  • Inhalation is considered to the primary mode of infection, where conidia or hyphal fragments are inhaled with subsequent conversion to the yeast form.
  • Percutaneous inoculation may also occur with organisms entering tissue via traumatic inoculation, but generally solitary lesions should be considered part of systemic disease.
  • The virulence factor Blastomyces adhesion-1 (Bad1) is expressed by the yeast form, which is followed by uptake by phagocytic cells.
  • Affected macrophages show downregulation of tumor necrosis factor production, and thus there is a delay in activation of host cell-mediated immunity.
  • Cell-mediated immunity play a major role in the clearance of B. dermatitidis within the host, with apparent minimal reliance on humoral immunity.
  • Dissemination is believed to occur via the vascular and lymphatic routes.

Timecourse

  • Typical incubation period from inhalation of conidia to development of clinical signs is 4-6 weeks.
  • There are however reports of months to years between presumed exposure to the development of clinical signs, owing to both reactivation and latent infection.

Epidemiology

  • While most veterinary cases are considered sporadic, outbreaks of blastomycosis have been reported in humans.
  • Animals housed outdoors in an environment with a high load of Blastomyces conidia may be at higher risk of infection.
  • Recent soil disruption events, eg new housing developments, and recent rainfall are considered as important epidemiological risk factors favoring outbreaks in endemic regions.

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.
  • Mazi P B, Rauseo A M & Spec A (2021) Blastomycosis. Infect Dis Clin North Am 35 (2), 515-530  PubMed.
  • Le K, Beaufrere H, Laniesse D et al (2019) Diagnosis and long-term management of blastomycosis in two ferrets (Mustela putorius furo). J Exotic Pet Med 31, 39-44 PubMed.
  • Darrow B G, Mans C, Drees R et al (2014) Pulmonary Blastomycosis in a domestic ferret (Mustela putorius furo). J Exotic Pet Med 23 (2), 158-164 PubMed.
  • Parker K, Snead E, Anthony J & Silver T (2013) Oronasal blastomycosis in a golden retriever. Can Vet J, 54 (8), 748-52 PubMed.

Other sources of information

  • Gaunt M C & Evason M (2019) Blastomyces dermatitidis/Blastomycosis. In: Infectious Diseases of the Dog and Cat: A Color Handbook. Eds: Weese J S & Evason M. CRC Press, USA.
  • Fox J G (2014) Mycotic Diseases. In: Biology and Diseases of the Ferret. Eds: Fox J G & Marini R P. Wiley Blackwell, USA. pp 573-586.
  • Chengappa M M & Pohlman L M (2013) Agents of Systemic Mycosis. In: Veterinary Microbiology. Eds: McVey D S, Kennedy M & Chengappa M M. 3rd edn. Wiley Blackwell, USA. pp 433-447.

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