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Blastomycosis |
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Blastomyces dermatitidis
- moist soil
- Wisconsin is endemic area - also Kentucky and Tennessee
- Equal distribution in males and females
- Most dogs reside within 500 yd water
- Ask if client visits summer home in endemic area if dog has unexplained respiratory disease
Pathogenesis
- Inhaled - moist organic soil, hyperendemic areas
- Transforms into yeast, resistant to killing
- Respiratory disease can be mild or inapparent
- Disseminates to skin, eyes
- Causes intense local inflammation
Pathology
- pyogranulomatous
- Broad-based budding yeast
- Surrounded by inflammatory cells -- PMNs
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Pathogenesis of Fungal Disease |
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Systemic mycoses
- Virulent dimorphic pathogens (deep mycoses)
- Opportunistic infections
Subcutaneous mycoses
- Sporotrichosis
- Mycetoma and others
Cutaneous mycoses
- Dermatophytes -- "Ringworm"
- Mycotoxicoses - ingestion of toxins
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Overview of Systemic Mycoses |
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- Blastomycosis - Blastomyces dermatitidis
- Histoplasmosis - Histoplasma capsulatum
- Coccidioidomycosis - Coccidioides immitis
- All three are dimorphic
- Grow as mold in soil, or at room temp in lab
- Grow as yeast-like structure in tissue
- Soil -- reservoir of fungus
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Pathogenesis of Systemic Mycoses |
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- Spores inhaled -- transform into yeast in lung
- Can disseminate to other body sites
- Chronic infection
- Require cellular immunity for protection -- Ab response not protective
- Treatment - itraconazole, or amphotericin B,or amphotericin B with ketoconazole
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Diagnosis of Blastomycosis |
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- Visualize yeast in clinical material
- Exudate
- Tracheal wash
- Culture -- not done routinely, biohazard
- Reference lab will grow on BHI or blood agar
- Supplement with antibiotics, incubate at 25 C
Serology
- AGID - antigen A, 1:4 or higher is presumptive
- ELISA, RIA -- Wi-1 Ag, immunodominant
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Treatment of Blastomycosis |
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Itraconazole
- Given orally, less toxicity than Amphotericin B
Amphotericin B
- Toxic, monitor kidney function - BUN, creatinine
- Must give i.v. as suspension
Ketoconazole
- Combination therapy with Amphotericin
- Treatment always prolonged and costly!
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Public Health Concerns |
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- Humans and dogs have contracted blastomycosis from a shared exposure
- Dogs are not contagious for people!
- Common environmental source of fungus
+ Hunting parties
+ Hiking, summer homes
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Blastomycosis in other species |
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- Rare in cats, horses, pinnipeds, other species
- Doesn’t occur in cattle -- Why?
Human beings
- Pulmonary disease usually apparent
- Skin lesions - granulomatous, may be confused with skin cancer
- Need to diagnose promptly -- can disseminate and be fatal if left untreated
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Clinical Case |
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- The SVM received an urgent call for help from a man near Eagle, WI who raises Huskies and trains them for dogsled racing.
- In a colony of 30 adult dogs, there were 5 confirmed and 2 suspected cases of blasto over a 9 month period. All but 1 were female.
- 4 of the 5 confirmed cases died, all female
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Case Study |
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- Seven mo old Cockapoo became lethargic, developed cough tinged with blood, six weeks after trip to Bayfield, WI.
- First vet - diagnosed bacterial pneumonia, treated with antibiotics, no improvement.
- 2nd vet - Tried different antibiotic. No improvement. One wk later took X-ray of lung, saw "gas bubbles."
- Owner brought pup to VMTH. Attending vet student asked if pup had been up north.
- Re-examined X-ray, presumptive diagnosis of fungal pneumonia. Did lung aspirate, saw large thick-walled budding yeast.
- Started amphotericin B, but condition deteriorated and the pup was euthanized.
- Owner had asked first 2 vets about Blasto , but they said it was “too rare”.
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