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Histoplasmosis |
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Histoplasma capsulatum - dimorphic
- Endemic in Mississippi and Ohio River valleys
- Grows in bird guano
- Does not infect birds!
- High percentage of skin test positive in endemic areas
Grows as intracellular yeast in macrophages
- Not encapsulated
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Canine Histoplasmosis |
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Thought to cause infection by inhalation
- Causes respiratory disease
- Tends to disseminate to GI. tract
- Can visualize intracellular yeast in tissue
Infection probably common in endemic areas
- Respiratory disease - often mild or inapparent
- Serious clinical disease smaller percentage of those infected
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Histoplasmosis - other species |
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- Cats, horses, etc..
- Doesn’t occur in cattle
Human histoplasmosis
- Respiratory disease - usually mild, self-limiting
- Can disseminate to eyes, adrenals
- Can have vision sequelae
Epidemics - related to demolition of buildings, stirinng of contaminated dirt
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Histoplasmosis |
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Pathology
- Tends to from granulomatous lesions
- Small intracellular yeast in macrophages
- Can have small miliary lesions
Diagnosis
- Visualize yeast in mac in rectal scraping, tracheal wash
- Serology - may indicate prior infection
- Culture - biohazard
Treatment
Dimorphism
- Grows as mold in environment
- Microconidia are inhaled
- Multiply as yeast in macrophages
Can duplicate dimorphism in vitro
- Incubate on rich medium (BHI) - need cysteine
- Incubate at 37 C
- May be partial transition
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Case Report |
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History:
- 6 mo old female Spitz
- Chronic cough for 4 mo
- Occasional vomitting, diarrhea, distended abdomen
- Fever of 104 for past month
- Distemper vacciaanation 4 weeks ago
- Listless, but good appetite
- Lung sounds: congestion, mucous rales
- Pale oral mucosa, bleeding gums
Radiology:
- Liver - markedly enlarged
- Lungs - Patchy infiltration throughout lung field, which is strongly suggestive of a pneumonia which may be either bacterial or fungal in origin. The possibility of lymphosarcoma cannot be eliminated.
- Because of debilitated state, owner elects euthanasia.
Necropsy
- Lungs - edematous, contained many white firm nodules diffusely distributed throughout lung. An impression smear shows macrophages with intracellular yeasts.
- Liver - enlarged, congested, loss of lobules, vacuolated hepatocytes, many yeast in Kupffer cells
- Bone marrow, spleen - many intracellular yeast
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