A pulmonary disease caused by inhaling spores of the dimorphic fungus Blastomyces dermatitidis.
Exists in yeast form at 37*C and in mycelial form 25*C to 30*C
Yeast cell are 8-15 microm diameter with a highly refractive cell wall.
Symptoms result from pneumonia or from dissemination to multiple organs, most commonly the skin.
Symptoms can range from mild influenza like process to cough with sputum production, dyspnea and rarely respiratory distress syndrome.
Respiratory distress syndrome may occur particularly in patients with diabetes in those who’ve had prior antimicrobial therapy.
The fungi can spread hematogenously and cause extrapulmonary disease.
Exposure occurs primarily by inhalation and pulmonary involvement is the most common disease manifestation.
Diagnosis is clinical, by chest x-ray, or both and is confirmed by laboratory identification of the fungi.
Endemic area for blastomycosis includes Ohio–Mississippi River valleys, Northern Midwest, Upstate New York, Southern Canada that borders the Great Lakes.
Infections also occurs in the Middle East and Africa.
Infection may be more common and severe in an immunocompromised host.
Disseminate infection is more common in immunocompromised hosts.
Can be an asymptomatic, acute or chronic pulmonary manifestation and can mimic cancer, infection with pyogenic bacteria, Mycobacterium tuberculosis or fungi.
Less common than histoplasmosis or coccidioidomycosis.
Blastomyces dermatitidis grows as a mold at room temperature.
A thermally dimorphic fungus, typically endemic in Mississippi River basin and Great Lakes region.
Blastomyces dermatitidis is a soil-based fungus, associated with river banks, especially doing post rainfall days during late spring and summer months.
Conidia aerosolize and are inhaled into alveoli, where conversion to yeast phase occurs.
Alveolar macrophages phagocytize conidia an attempt to prevent transition into yeast.
Hematogenous spread can be seen in disseminated disease.
The process can be seen as a summer cold and in severe cases mortality is reported as high as 30%.
Blastomyces dermatitidis grows in soil enriched with animal excreta.
Blastomyces dermatitidis grows in moist, decaying, acidic organic material, often near rivers.
Inhaled spores convert into large invasive yeasts, which form characteristic broad-based buds.
Human infection occurs to inhalation of conidia causing asymptomatic or symptomatic infectious illness.
Primary cutaneous blastomycosis may result if the accidental inoculation or dog bites.
Pulmonary infection may remain localized or disseminate via the blood stream.
Hematogenous dissemination can cause involvement of the skin, kidneys, bones, subcutaneous tissues, prostate, epididymides, testes, vertebrae, brain, oral or nasal mucosa, thyroid, lymph nodes, and bone marrow.
Lung involvrmrnt may be asymptomatic or cause an acute, self-limited disease that often goes unnoticed.
Pregnant patients are more likely to have disseminated fungal disease.
Pulmonary involvement may result in a chronic infection.
Pulmonary involvement symptoms include cough, chest pain, dyspnea, fever, chills, and sweats.
Pleural effusion may occur, rarely.
4% have involvement of the skeletal system.
The lungs are the most common site of involvement, followed by skin, bone, and the genitourinary system.
May mimic malignancy as it can present is a dense mass.
Progressive pulmonary involvement may lead to acute respiratory distress syndrome.
Skin lesions are the most common extrapulmonary lesions.
Hematogenous dissemination leads to extrapulmonary blastomycosis and skin lesions occur in 80% of patients.
Extrapulmonary lesions occur in immunocompetent as well as immunosuppressed individuals.
Primary cutaneous blastomycosis is rare but can occur by direct inoculation with B. dermatitis.
Both primary and secondary cutaneous lesions can manifest as papules, pustules, ulcers, nodules, or veroucous lesions that can be misdiagnosed is squamous cell carcinoma.
Skin lesions often show pseudo epitheliomatous hyperplasia with intraepidermal microabscesses and occasionally round yeast forms.
The disease may disseminate into the GU tract, bone, and CNS.
Dissemination risks are increased in pregnant women and those who are immunosuppressed, including recipients is solid organ transplants, those who have advanced HIV, and patients on prolonged corticosteroid therapy.
X-ray manifestations include focal masses, nodules, interstitial lung disease, airspace consolidation, and cavitary lesions.
With acute blastomycosis patients tend to have a airspace consolidation on x-rays and imaging studies, and those with chronic infection may present with mass lesions.
Pleural effusions and lymphadenopathy are rare manifestations of blastomycosis.
Untreated blastomycosis is usually slowly progressive and is rarely ultimately fatal.
Cultures of infected material may lead to diagnosis.
Diagnosis requires a high index of suspicion in endemic areas.
Diagnosis can be made by isolating B dermatitisis from respiratory specimens or tissue cultures.
Staining with periodic acid-Schiff and methenamine silver and direct visualization of B. dermatitis tissue specimens in usual diagnostic methods, especially in extrapulmonary disease.
Urine testing B. dermatitis antigen immunosassat has a sensitivity of 93% and the specificity of 79% for blastomycosis.
On histologic examination the yeast appears with broad-based budding.
Can be diagnosed by detection of Blastomyces antigen in urine and blood.
Treatment includes antifungal agenst such as itraconazole for mild to moderate disease.
Recommended amphotericin or amphotericin deoxcholate for moderate to severe disease, followed by 6-12 months of oral itraconazole.
Treatment of moderate to severe pulmonary or disseminated disease consists of amphotericin B for 1-2 weeks until symptoms abate, followed by itraconazole for 6 to 12 months.
For mild to moderate disease monotherapy with itraconazole for 6 to 12 months is recommended.
Serum levels of itraconazole should be assessed after 2 weeks to ensure adequate levels.
Blastomycosis antigen levels allows monitoring of treatment response.