Blastomycosis and Histoplasmosis

Question 1

What’s the causative agent for blastomycosis?

Answer 1

Blastomyces dermatitidis
- thick walled yeast, reproduce by budding

Question 2

Is blastomycosis contagious?

Answer 2

no

Question 3

What’s the pathogenesis of blastomycosis?

Answer 3

rain/dew/fog/ moisture, then disrupt soil – spores aerosolized - gets in to the lungs
- phagocytosis by alveolar macrophage
- stimulate cell mediated immunity – suppurative to pyogranulomatous inflammatory response
- if not controlled locally, transported to lungs - then can go through either lymphatic or blood to disseminate

Question 4

What are the clinical signs of blastomycosis?

Answer 4

non-specific signs: anorexia, fever, weight loss, depression
- Dogs: pulmonary signs (65-85%), diffuse lyhmphadenopathy (40-50%), cutaneous (30-50%), ocular (20-50%), lameness (25%), repro (5%), neuro (<5%)
- cats: cutaneous (large abscess) often noted, CNS involvement more common than dogs

• pulmonary signs = harsh cough, hypoxemia, pleural effusion = uncommon

Question 5

How is blastomycosis diganosed?

Answer 5

characteristic thick-walled yeast is easily seen on cytology
- hypoproteinemia, proteinuria – urine antigen test
- hypercalcemia
- hypercoagulable

CXR: interstitial pattern
Rads: osteomyelitis – periosteal proliferation and swelling, fore limbs > hind limbs, tend to be at the epiphysis, below stifle/ elbow

Question 6

What are some differential for perihilar lymphadenopathy?

Answer 6

blastomycosis
histoplasmosis
coccidioidomycosis

Question 7

How specific is the blastomycosis urine antigen test?

Answer 7

can still cross react with histoplasmosis and other fungal infections
- serum is less sensitive and specific

Question 8

How is blastomycosis treated?

Answer 8

anti-fungal
- itraconazole or fluconazole (less $, crosses BBB etc, but less effective overall)
- amphotericin B if there is systemic involvement
- the lipid formation ($$$) is good for CNS involvement
- deoxycholate form is less expensive, but more toxicity (azotemia)

Question 9

What are some adverse effects of azoles?

Answer 9

GI signs
increase in liver enzymes
secondary cutaneous vasculitis

Question 10

What’s the success rate of blastomycosis treatment?

Answer 10

70-75% cure will treatment
can still relapse; 20% recurrence rate

Question 11

What’s the prognosis of blastomycosis?

Answer 11

Negative prognostic factor = hypoxemia 3+ body involvement

Question 12

What’s the public health significance of blastomycosis?

Answer 12

it’s not contagious
clusters with people = common environment

Question 13

What’s the causative agent of histoplasmosis?

Answer 13

histoplasma capsulatum
fungus
not contagious

Question 14

What’s the pathophysiology of histoplasmosis?

Answer 14

similar to blastomycosis
but also has an ingestive/ GI component, esp in dogs
- phagocytosed by macrophages – facultative intracellular organisms – can spread via lymphatics or blood = disseminated disease
- required cell mediated immunity to clear infection
- most infection is likely subclinical

Question 15

What are the clinical signs of histoplasmosis?

Answer 15

Cats:
- <4yo
- insidious onset, non specific signs
- depression, fever, anorexia, weight loss
- pulmonary signs <50%, cough = uncommon
- similar to blastomycosis, but most signs are less common

Dogs:
- <4yo
- inhalation is likely the more common route of infection, but GI signs are most common
- fever, anorexia, weight loss, depression
- respiratory signs <50%

Question 16

What are some lab abnormalities noted with histoplasmosis?

Answer 16

• thrombocytopenia (1/2 dogs, 1/3 cats)
• hypoalbuminemia = most consistent lab finding
• hypercalcemia more common in cats than dogs

Question 17

What is noted on rads for histoplasmosis?

Answer 17

Hilar lymphadenopathy = common in dogs, unusual in cats
- alveolar infiltrate = rare
- bone lesion: carpal/ tarsus; cats effect with osseous lesions more than dogs

Question 18

How is histoplasmosis diagnosed?

Answer 18

cytology
fungal culture is rarely needed
- antibody = ineffective method for diagnosis – both false (+) and false (-) are common
- can use the same urine antigen test as blastomycosis – positive = fungal infection

Question 19

How is histoplasmosis treated?

Answer 19

with pulmonary lesions only, likely self-limiting BUT since it can spread systemically, treatment is recommended
- similar to treating blastomycosis
- cats: itraconazole +/- amphotericin B
- dogs: ketoconazole
- need regular monitoring and post-tx monitoring
- response = resolution of clinical signs

Question 20

What’s the prognosis of histoplasmosis?

Answer 20

for pulmonary lesions only = good
- disseminated = fair to good for cats
- GI or severe dissemination in dogs = guarded