Blastomyces Parvus

''Emmonsia parva'' (formerly ''Chrysosporium parvum'') is a filamentous, saprotrophic fungus and one of three species within the genus ''Emmonsia''. The fungus is most known for its causal association with the lung disease, adiaspiromycosis which occurs most commonly in small mammals but is also seen in humans. The disease was first described from rodents in Arizona, and the first human case was reported in France in 1964. Since then, the disease has been reported from Honduras, Brazil, the Czech Republic, Russia, the United States of America and Guatemala. Infections in general are quite rare, especially in humans.

Ecology

''Emmonsia parva'', ''E. crescens'', and ''E. pasteuriana'' together comprise the genus ''Emmonsia'', however they exhibit different ecological characteristics. Whereas ''E. crescens'' is found worldwide, ''E. parva'' is restricted to areas in North and South America, Eastern Europe, Australia and regions in Asia. The fungus is primarily a saprotroph, deriving its nutrition from dead material. It is also soil-dwelling where it release spores into the air. Because of this the main targets of infection are small burrowing mammals such as rodents, although infection of larger mammals such as humans has been documented. Some of the known animal species that it can infect include the beaver, mink, weasel, wood rat, pine marten, pine squirrel, cottontail rabbit, muskrat, skunk, white-tailed mouse and the rock rabbit. The fungus is closely related to the genus ''Blastomyces''.

Growth and morphology

The fungus is dimorphic growing in two distinct forms. It grows as hyphae at room temperature, but when conidia are transferred to 40 °C they convert to larger adiaspores. It has no teleomorphs and no sexual stage. It does not have any particular growth requirements in terms of culture media, but it is known to grow well on pablum cereal agar, potato dextrose agar (PDA) and phytone yeast extract agar. They also grow well on Sabouraud dextrose agar at 25 °C. Growth is slightly inhibited when grown in media containing cycloheximide. ''E. parva'' grows at a moderate pace, slower than ''E. crescens''. After 21 days of growth at room temperature colony diameters range from 36 to 85 mm. The colonies are smooth and velvety and are white with tan centers from a top view and cream from the bottom. Hyphae in this form are septate and hyaline. The conidiophores they produce are unicellular, thick-walled (2 μm), and usually simple with a single terminal conidium also called an aleurioconidium. The conidiophore is also known to occasionally branch into 1-3 sections each bearing its own conidium. Before differentiating into adiaspores, the conidia measure 2-4 μm in diameter and are shaped either ovoid, subglobose or pyriform with glabrous walls. After growth at 40 °C the conidia morph into their adiaspore form enlarging to approximately 25 μm in vitro and 40 μm in vivo. These adiaspores are uninucleate