At room temperature is takes the mycelial form shown below, forming a single conidium that looks kind of like a lollipop. In this form, and with the typical lactophenol cotton blue stain, it is known as the Big Blue Broad Based Budding yeast - Blasto . Each yeast is multinucleate with 2-5 nuclei per cell. The mechanism for the phase transition is unknown, but the reason for the transition is quite clear, as described below. . The gymnothecium, however, has an outer covering that is more loosely woven, so that ascospores can fall out without having the covering degraded by other microbes.
Blastomycosis starts out as a lung infection caused by inhalation of the conidia.
The fungus evades the body's immune system by changing its surface antigens. The patient may have severe presenting symptoms or may be inapparent infection that resolves spontaneously or disseminates to another location. If symptoms do appear, the incubation period may be long - 21 to 106 days. It starts with mild progressive respiratory infection with a dry cough, some pleuritic pain, hoarseness, and a low grade fever, symptoms that overlap many other diseases, such as tuberculosis or chronic histoplasmosis . If the primary pulmonary infection does not resolve, severe progressive blastomycosis can result.