ISSN 2398-2969      

Histoplasmosis

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Introduction

  • Cause: systemic fungal infection caused byHistoplasma capsulatum Histoplasma capsulatum.
  • Endemic in many temperate and subtropical regions of the world.
  • Organism is soil-borne; microconidia of the mycelial form are infectious.
  • Signs: chronic large or small bowel diarrhea, respiratory signs, ocular signs, cutaneous lesions, lameness, occasional CNS signs.
  • Diagnosis: cytology, histopathology.
  • Treatment: itraconazole, ketoconazole, fluconazole, amphotericin B.
  • Prognosis: good for localized and guarded for generalized infections in debilitated animals.

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.

Specific

  • Living or traveling in an endemic area.
  • Hunting dogs.

Pathophysiology

  • Infection occurs via inhalation of microconidia. Once in the lungs, the organism converts to a yeast phase and spreads to regional lymph nodes and other organs of the body.
  • Most common organs affected are the lungs, lymph nodes, gastrointestinal tract, bone marrow, liver, spleen, adrenal glands, and eyes.
  • Organs affected occasionally are the long bones, skin, and central nervous system.
  • Organisms are engulfed by phagocytic white blood cells. If host immunity is overwhelmed the organism replicates with the reticuloendothelial system, resulting in widespread disease and death.

Timecourse

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

Diagnosis

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Treatment

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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). JAVMA 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.
  • Fisher M A, Bono J L, Abuodeh R O, Legendre A M & Scalarone G M (1995) Sensitivity and specificity of an isoelectric focusing fraction of Blastomyces dermatitidis yeast lysate antigen for the detection of canine blastomycosis. Mycoses 38 (5-6), 177-182 PubMed.
  • Huss B T, Collier L L, Collins B K et al (1994) Polyarthropathy and chorioretinitis with retinal detachment in a dog with systemic histoplasmosis. J Am Anim Hosp Assoc 30 (3), 217-224 VetMedResource.
  • Kowalewich N, Hawkins E C, Skowronek A J, Clemo F A (1993) Identification of Histoplasma capsulatum organisms in the pleural and peritoneal effusions of a dog. JAVMA 202 (3), 423-426 PubMed.
  • 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). JAVMA 193 (11), 1443-1447 PubMed.

Other sources of information

  • Taboada J (2002)Systemic mycoses.In: Morgan RV, Bright R N, Swartout MS (eds)Handbook of Small Animal Practice. 4th Ed. W B Saunders, Philadelphia, pp1075-1089.
  • Wolf A M (1998)Histoplasmosis.In: Greene CE (ed):Infectious diseases of the Dog and Cat. 2nd Ed. W B Saunders, Philadelphia, pp 378-383.

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