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.
Blastomycosis seems more probable as these young people in Late Woodland and Mississippian times may have been affected because they were spending more time cultivating plants than their Middle Woodland predecessors had done. If true, it would be another severe penalty Late Woodland people had to pay as they shifted to agriculture as a way of life, and it would be a contributing factor to shortening their lifespans compared to those of the Middle Woodland people.Blastomycosis was first described by Thomas Caspar Gilchrist in 1894, as a skin disease. Because of this, blastomycosis is sometimes called "Gilchrists disease". Gilchrist initially identified the cause of the disease as a protozoan, but later correctly identified it as a fungus. In 1898 he and William Royal Stokes published the first description of Blastomyces dermatitidis. Gilchrist referred to the disease as "blastomycetic dermatitis". The systemic spread of blastomycosis was first described in 1902, in a case that had been misdiagnosed as a combination of tuberculosis and a blastomycosis skin infection. In 1907, the dimorphic nature of the Blastomyces fungus was first identified. In 1912, the first case of canine blastomycosis was reported.Prior to the 1930s, blastomycosis was not clearly distinguished from similar fungal conditions. A paper by Rhoda Williams Benham in 1934 distinguished the causative agent of blastomycosis from cryptococcosis and coccidioidomycosis.In the early 1950s, blastomycosis was first determined to be a primarily respiratory disease, with most skin lesions caused by systemic spread from an initial lung infection.