In 1952, the first documented case outside North or Central America, in Tunisia, was reported. The 1950s also saw the first introduction of antifungal drugs including amphotericin B. Before 1950, the fatality rate for disseminated blastomycosis was 92%, and treatment options were limited to iodide compounds, radiation therapy, and surgery. The first azole antifungal drug, ketoconazole, was developed in the 1970s and approved in the United States in 1981.Prior to 2013, the only species known to cause blastomycosis was B. dermatitidis. Since that time, genomic analysis has identified multiple other Blastomyces species causing blastomycosis, including B. gilchristii (2013), B. helicus (reassigned from the genus Emmonsia in 2017), B. percursus (2017), and B. emzantsi (2020). Other animals
Blastomycosis affects a broad range of mammals. As with humans, most animals that become infected were formerly healthy and immunocompetent. Dogs are frequently affected; blastomycosis is eight to ten times more common in dogs than in humans. Sporting and hound breeds are at the greatest risk. Cats and horses can also be infected. Cats with feline immunodeficiency virus are particularly at risk. However, the overall risk of blastomycosis in cats is 28 to 100 times lower than in dogs. Cases of blastomycosis have also been reported in captive lions and tigers, in a wild North American black bear, and in marine mammals such as the Atlantic bottlenose dolphin.The nonspecific symptoms that make blastomycosis difficult to diagnose in humans also complicate veterinary diagnosis. Cats in particular are often only diagnosed after death.Dogs and humans frequently acquire blastomycosis from the same exposure event.
Because the symptoms are variable and nonspecific, blastomycosis is often not even considered in differential diagnosis until antibacterial treatment has failed, unless there are known risk factors or skin lesions. The disease may be misdiagnosed as a carcinoma, leading in some cases to surgical removal of the affected tissue. Upper lung lobes are involved somewhat more frequently than lower lobes. If untreated, many cases progress over a period of months to years to become disseminated blastomycosis. Blastomycosis in the lungs may present a variety of symptoms, or no symptoms at all. If symptoms are present they may range from mild pneumonia resembling a pneumococcal infection to acute respiratory distress syndrome (ARDS). Common symptoms include fever, chills, headache, coughing, difficulty breathing, chest pain, and malaise. Without treatment, cases may progress to chronic pneumonia or ARDS.ARDS is an uncommon but dangerous manifestation of blastomycosis. It was seen in 9 of 72 blastomycosis cases studied in northeast Tennessee. Such cases may follow massive exposure, such during brush clearing operations. In the Tennessee study, the fatality rate was 89% in the ARDS cases, but only 10% in the non-ARDS cases.In disseminated blastomycosis, the large Blastomyces yeast cells translocate from the lungs and are trapped in capillary beds elsewhere in the body, where they cause lesions. The skin is the most common organ affected, being the site of lesions in approximately 60% of cases. The signature image of blastomycosis in textbooks is the indolent, verrucous or ulcerated dermal lesion seen in disseminated disease. Osteomyelitis is also common (12–60% of cases).