Blastomycosis or blasto is a fungal infection caused by inhaling spores of a Blastomyces fungus. Only about half of people with the disease have symptoms, which can include fever, cough, night sweats, muscle pains, weight loss, chest pain, and feeling tired. Symptoms usually develop between three weeks and three months after breathing in the spores. Most blastomycosis infections affect the lungs. In 25 to 40% of cases, the infection also spreads to other parts of the body, such as the skin, bones or central nervous system. Although blastomycosis is especially dangerous for those with weak immune systems, most people diagnosed with blastomycosis have healthy immune systems.Blastomyces dermatitidis is found in the soil and decaying organic matter like wood or leaves. Outdoor activities like hunting or camping in wooded areas increase the risk of developing blastomycosis. There is no vaccine, but the risk of the disease can be reduced by not disturbing the soil. Treatment is typically with an azole drug such as itraconazole for mild or moderate disease. In severe cases, patients are treated with amphotericin B before azole treatment. In either event, the azole treatment lasts for 6–12 months. Overall, 4-6% of people who develop blastomycosis die; however, if the central nervous system is involved, this rises to 18%. People with AIDS or on medications that suppress the immune system have the highest risk of death at 25-40%.Blastomycosis is endemic to the eastern United States and Canada, especially the Ohio and Mississippi River valleys, the Great Lakes, and the St. Lawrence River valley.
Pathogenesis
Inhaled conidia of Blastomyces are phagocytosed by neutrophils and macrophages in alveoli. Some of these escape phagocytosis and transform into yeast phase rapidly. Having thick walls, these are resistant to phagocytosis. Once they have transitioned to the yeast phase, the Blastomyces cells express the protein BAD-1, which helps the yeast cells attach to host cells, and also impairs activation of immune cells while inhibiting release of tumor necrosis factor. In lung tissue, the cells multiply and may also disseminate through blood and lymphatics to other organs, including the skin, bone, genitourinary tract, and brain. The incubation period for pulmonary blastomycosis is 3 to 15 weeks, although 30–50% of infections are asymptomatic. Diagnosis
Because the symptoms of blastomycosis resemble those of many other conditions, including tuberculosis and lung cancer, diagnosis is often delayed. In 40% of cases, the diagnosis takes more than a month. A rapid diagnosis can however be made based on microscopic examination of sputum samples or samples obtained from a tissue biopsy or bronchoalveolar lavage.Once suspected, the diagnosis of blastomycosis can usually be confirmed by demonstration of the characteristic broad based budding organisms in sputum or tissues by KOH prep, cytology, or histology. Tissue biopsy of skin or other organs may be required in order to diagnose extra-pulmonary disease. Blastomycosis is histologically associated with granulomatous nodules. Commercially available urine antigen testing appears to be quite sensitive in suggesting the diagnosis in cases where the organism is not readily detected.