Canis ISSN: 2398-2942

Fungal lung disease: histoplasmosis

Contributor(s): Prof Susan Bunch, Rhea Morgan, Elizabeth Rozanski

Introduction

  • Systemic mycotic infection.
  • Etiological agent:dimorphic fungus,Histoplasma capsulatum Histoplasma capsulatum.
  • Signs of infection:anorexia, weight loss, fever, cough, hepatomegaly, diarrhea, cough, dyspnea, ocular signs, cutaneous lesions, lameness.
  • Route of infection:inhalation, possibly oral.
  • Diagnosis:characteristic pulmonary, ocular, and gastrointestinal changes.
  • Idenfication:of organism in cytological or histopathological samples.
  • Treatment:itraconazole and other antifungal agents.
  • Prognosis:Guarded for generalized disease, good for localized disease.

Pathogenesis

Etiology

Predisposing factors

General
  • Many animals may be exposed, develop subclinical infections and spontaneously recover.
  • Overwhelming infection and compromise of the immune system may lead to disseminated infection.
  • Exposure to a common source outside (eg bird guano), in an endemic area.
  • Young dogs.

Pathophysiology

  • The dimorphic yeast organism usually gains entry into the body via inhalation of the microconidia.
  • Although unconfirmed, infection may possibly be acquired orally.
  • Organism converts into yeast form at body temperature.
  • Yeast cells are phagocytized by cells of the host monocyte-macrophage system and then replicate intracellularly.
  • Infection usually cleared by host's cell-mediated immune mechanisms.
  • If overwhelming infection and/or host immunodeficiency, infection may become generalized.
  • Infection first develops in the lungs, then disseminates via hematogenous and lymphatic routes to rest of body.
  • Specific target organs include the gastrointestinal tract, the respiratory tract, lymph nodes, bone marrow, adrenal glands, eyes, liver and spleen.

Timecourse

  • Incubation time = 12-16 days.
  • Duration = weeks to months.

Epidemiology

  • Exists in soil, rich in organic matter within the endemic areas.

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.
  • Schulman R L, McKiernan B C & Schaeffer D J (1999) Use of corticosteroids for treating dogs with airway obstruction secondary to hilar lymphadenopathy caused by chronic histoplasmosis: 16 cases (1979-1997). J Am Vet Med Assoc 214 (9), 1345-1348 PubMed.
  • Clinkenbeard K D, Wolf A M, Cowell R L et al (1998) Canine disseminated histoplasmosis. Compend Contin Educ Pract Vet 11 (11), 1347-1357 VetMedResource.
  • Clinkenbeard K D, Tyler R D, Cowell R L (1989) Thrombocytopenia associated with disseminated histoplasmosis in dogs. Compend Contin Educ Pract Vet 11 (3), 301-304 VetMedResource.
  • Clinkenbeard K D, Cowell R L & Tyler R D (1988) Disseminated histoplasmosis in dogs: 12 cases (1981-1986). J Am Vet Med Assoc 193 (11), 1443-1447 PubMed.

Other sources of information

  • Taboada J (2002)Systemic mycoses.In: Morgan R V, Bright R N, Swartout M S (eds)Handbook of Small Animal Practice.4th Ed. W B Saunders, Philadelphia, pp 1075-1089.
  • Wolf A M (1998)Histoplasmosis.In:Infectious diseases of the Dog and Cat.Ed C E Greene. Philadelphia: W B Saunders. pp 378-383.


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