''Emmonsia parva'' (formerly ''Chrysosporium parvum'') is a filamentous,
saprotroph
Saprotrophic nutrition or lysotrophic nutrition is a process of chemoheterotrophic extracellular digestion involved in the processing of decayed (dead or waste) organic matter. It occurs in saprotrophs, and is most often associated with fungi ...
ic 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
Arizona is a U.S. state, state in the Southwestern United States, Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the nort ...
,
and the first human case was reported in
France
France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...
in 1964.
Since then, the disease has been reported from
Honduras
Honduras, officially the Republic of Honduras, is a country in Central America. It is bordered to the west by Guatemala, to the southwest by El Salvador, to the southeast by Nicaragua, to the south by the Pacific Ocean at the Gulf of Fonseca, ...
,
Brazil
Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...
, the
Czech Republic
The Czech Republic, also known as Czechia, and historically known as Bohemia, is a landlocked country in Central Europe. The country is bordered by Austria to the south, Germany to the west, Poland to the northeast, and Slovakia to the south ...
,
Russia
Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...
, the
United States of America
The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 states and a federal capital district, Washington, D.C. The 48 contiguo ...
and
Guatemala
Guatemala, officially the Republic of Guatemala, is a country in Central America. It is bordered to the north and west by Mexico, to the northeast by Belize, to the east by Honduras, and to the southeast by El Salvador. It is hydrologically b ...
.
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
Beavers (genus ''Castor'') are large, semiaquatic rodents of the Northern Hemisphere. There are two existing species: the North American beaver (''Castor canadensis'') and the Eurasian beaver (''C. fiber''). Beavers are the second-large ...
,
mink
Mink are dark-colored, semiaquatic, carnivorous mammals of the genera ''Neogale'' and '' Mustela'' and part of the family Mustelidae, which also includes weasels, otters, and ferrets. There are two extant species referred to as "mink": the A ...
,
weasel
Weasels are mammals of the genus ''Mustela'' of the family Mustelidae. The genus ''Mustela'' includes the least weasels, polecats, stoats, ferrets, and European mink. Members of this genus are small, active predators, with long and slend ...
,
wood rat,
pine marten
The European pine marten (''Martes martes''), also known as the pine marten, is a mustelid native to and widespread in most of Europe, Asia Minor, the Caucasus, and parts of Iran, Iraq, and Syria. It is listed as Least Concern on the IUCN Red Lis ...
,
pine squirrel
Pine squirrels are squirrels of the genus ''Tamiasciurus'', in the Sciurini tribe, of the large family Sciuridae.
Species
This genus includes three species:
*''Tamiasciurus douglasii'' — Douglas squirrel
**''T. d. mearnsi'' — Mearns's sq ...
,
cottontail rabbit
Cottontail rabbits are in the ''Sylvilagus'' genus, which is in the family Leporidae. They are found in the Americas. Most ''Sylvilagus'' species have stub tails with white undersides that show when they retreat, giving them their characterist ...
,
muskrat
The muskrat or common muskrat (''Ondatra zibethicus'') is a medium-sized semiaquatic rodent native to North America and an introduced species in parts of Europe, Asia, and South America.
The muskrat is found in wetlands over various climates ...
,
skunk
Skunks are mammals in the family Mephitidae. They are known for their ability to spray a liquid with a strong, unpleasant scent from their anal glands. Different species of skunk vary in appearance from black-and-white to brown, cream or gi ...
,
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
A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium.
Structure
A hypha consists of one o ...
at room temperature, but when
conidia
A conidium ( ; : conidia), sometimes termed an asexual chlamydospore or chlamydoconidium (: chlamydoconidia), is an asexual, non- motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also ...
are transferred to 40 °C they convert to larger
adiaspores.
It has no
teleomorph
In mycology, the terms teleomorph, anamorph, and holomorph apply to portions of the life cycles of fungi in the phyla Ascomycota and Basidiomycota:
*Teleomorph: the sexual reproductive stage (morph), typically a fruiting body.
*Anamorph: an ase ...
s 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