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Emmonsia spp.
(described by Ciferri and Montemartini in 1953)

 

Taxonomic classification

Kingdom: Fungi
Phylum: Ascomycota
Class: Euascomycetes
Order: Onygenales
Family: Onygenaceae
Genus: Emmonsia

Description and Natural Habitats

Emmonsia is a cosmopolitan filamentous fungus isolated from soil and some mammalian species, such as small rodents. It is frequently encountered as a dimorphic fungus due to its ability to produce a distinctive structure known as an adiaspore at 37-40°C. Emmonsia is an occasional cause of animal and human infections. Emmonsia crescens has been reported world-wide. Emmonsia parva is known to be endemic in Soutwestern USA, Australia, and Eastern Europe [531].

Species

The genus Emmonsia currently contains four species; Emmonsia parva, Emmonsia parva var. crescens, Emmonsia parva var. parva, and Emmonsia pasteuriana. Emmonsia parva is occasionally referred to as Chrysosporium parvum. Please see our detailed discussion about the classification of Emmonsia parva.

Pathogenicity and Clinical Significance

Emmonsia is the causative agent of adiaspiromycosis particularly in rodents [1079], and very rarely in humans [671]. Adiaspiromycosis is an asymptomatic pulmonary infection which may disseminate in immunocompromised hosts, such as patients with AIDS [643]. Adiaspiromycosis develops following inhalation of conidia of Emmonsia. These conidia, known as the adiaspores, enlarge in the alveoli and hinder regular pulmonary functions. Adiaspores do not reproduce and remain localized at their primary implantation site. They eventually become calcified and lead to a minimal reaction in the host tissue. Emmonsia parva var. crescens is the primary species isolated from humans while Emmonsia parva var. parva is mostly isolated from animals.

The other Emmonsia species, Emmonsia pasteuriana has recently been isolated from a cutaneous disseminated infection in an HIV-infected patient [878].

Macroscopic Features

Emmonsiagrows moderately rapidly and produces glabrous to velvety colonies. From the front, the colonies are white and may have buff to pale brown center. From the reverse, the color is cream to pale brown [1295] [2144].

Microscopic Features

Septate hyaline hyphae, conidiophores, and aleurioconidia are visualized. Adiaspores are formed only at 37-40°C and in vivo or on blood or brain heart infusion agar in vitro. Conidiophores are simple or may occasionally branch at right angles. Aleuriconidia are sessile or are located on slender stalks. They are unicellular, thin-walled, (sub)spherical, and 2-5 x 2-4 µm in size. These aleuriconidia are found solitary or may form two- to three-celled chains. At 37-40°C, the conidia tend to swell and give rise to thick-walled, big, liberated conidia known as adiaspores.

Adiaspores of the two varieties of Emmonsia parva tend to differ. The diameter of the adiaspores of Emmonsia parva var. parva may reach 25 µm in vitro and 40 µm in vivo. Adiaspores of Emmonsia parva var. crescens may be much more bigger. They may attain diameters of 70 µm and 700 µm in vitro and in vivo, respectively. Adiaspores of Emmonsia parva var. parva are uninucleate while those of Emmonsia parva var. crescens are multinucleate (up to several hundred nuclei). Emmonsia parva var. parva forms adiaspores at 40°C while Emmonsia parva var. crescens produces them at 37°C rather than 40°C [1295] [2144].

In contrast to the other species, Emmonsia pasteuriana does not produce adiaspores. Instead, budding cell-like structures are formed by this species on brain-heart infusion agar at 37°C.

Histopathologic Features

Adiaspores surrounded by small granulomes are visualized. Concentric layers of fibrous tissue is formed in later stages of the infection [531].

Compare to

Blastomyces dermatitidis
Chrysosporium spp.
Histoplasma capsulatum
Paracoccidioides brasiliensis
Sporotrichum spp.

Emmonsia parva and its two varieties must be differentiated from Blastomyces dermatitidis, Histoplasma capsulatum, and Paracoccidioides brasiliensis by the inability of Emmonisia spp. to convert to a yeast phase at 37°C. They are differentiated from Sporotrichum by their inability to produce large chlamydospores at 25°C [2144].

Laboratory Precautions

No special precautions other than general laboratory precautions are required.

Susceptibility

No data are available.

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References

531. de Hoog, G. S., J. Guarro, J. Gene, and M. J. Figueras. 2000. Atlas of Clinical Fungi, 2nd ed, vol. 1. Centraalbureau voor Schimmelcultures, Utrecht, The Netherlands.

643. Echavarria, E., E. L. Cano, and A. Restrepo. 1993. Disseminated adiaspiromycosis in a patient with AIDS. J Med Vet Mycol. 31:91-97.

671. England, D. M., and L. Hochholzer. 1993. Adiaspiromycosis: an unusual fungal infection of the lung. Report of 11 cases. Am J Surg Pathol. 17:876-886.

878. Gori, S., E. Drohuet, E. Gueho, M. Huerre, A. Lofaro, M. Parenti, and B. Dupont. 1998. Cutaneous disseminated mycosis in a patient with AIDS due to a new dimorphic fungus. J Mycol Med. 8:57-63.

1079. Hubalek, Z., J. Nesvadbova, and J. Halouzka. 1998. Emmonsiosis of rodents in an agroecosystem. Med Mycol. 36:387-390.

1295. Larone, D. H. 1995. Medically Important Fungi - A Guide to Identification, 3rd ed. ASM Press, Washington, D.C.

2144. St-Germain, G., and R. Summerbell. 1996. Identifying Filamentous Fungi - A Clinical Laboratory Handbook, 1st ed. Star Publishing Company, Belmont, California.



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