Research Highlights: The History of New Dimorphic Fungal Pathogen: Emergomyces

Potential model for exposure and pathogenesis of Emergomyces.

1) Emergomyces species exist in soil in a mold phase, from where 2) conidia are released and aerosolized. 3) Upon inhalation by humans, the conidia undergo a temperature-dependent transformation in the lungs to yeast-like cells that replicate by budding and are capable of causing pulmonary disease in susceptible individuals. 4) Yeast-like cells disseminate hematogenously in macrophages throughout the body, causing extrapulmonary disease. 5) Cutaneous disease is most frequently reported, although virtually any body site can be affected. Image Source: https://doi.org/10.1371/journal.ppat.1007977

Original Article: https://doi.org/10.1371/journal.ppat.1007977

  • In 1994, a woman from Italy with advanced HIV disease and widespread cutaneous lesions was diagnosed with an atypical disseminated mycosis.
  • Mycosis refers to a disease caused by fungal infection, such as ringworm or thrush.
  • A biopsy of skin tissue demonstrated small budding yeasts, resembling those of Histoplasma capsulatum, in addition to larger pleomorphic cells.
  • Histoplasma capsulatum is an environmental fungus and the most common endemic pulmonary mycosis in the United States.
  • Pleomorphic means able to assume different forms.
  • Moreover, the fungus that grew in culture had a dissimilar microscopic appearance.
  • The conidia were arranged in complex “florets” on slightly swollen stalks reminiscent of Emmonsia crescens (Eaparva) fungi for which the thermodependent phase is characterized by swollen, thick-walled, nonreplicating cells called adiaspores, usually observed in the lungs of small terrestrial mammals in a disease called adiaspiromycosis.
  • Conidium is a type of asexual reproductive spore of fungi usually produced at the tip or side of hyphae or on special spore-producing structures called conidiophores.
  • Adiaspiromycosis is a world wide airborne infection and is a pulmonary disease in humans caused by the fungus Chrysosporium parvum var crescens (Emmonsia parva) and it is caused by inhalation of spores of the saprophytic soil fungus.
  • Genetic analysis suggested the clinical isolate was related to Eacrescens, and the fungus was therefore described in 1998 as Eapasteuriana.
  • In 2013, following the introduction of molecular identification procedures in some South African laboratories, a dimorphic fungus most closely related to Eapasteuriana was found to be the cause of a disseminated mycosis in patients with advanced HIV disease.
  • Since then, infection with this fungus has been established to comprise the most frequently diagnosed dimorphic mycosis in South Africa.
  • In light of these reports, global collections were re-examined for dimorphic Emmonsia-like fungi.
  • Archived isolates were examined phenotypically and with genetic analyses based on ribosomal DNA sequences, ultimately leading to a taxonomic revision within the family Ajellomycetaceae.
  • The Ajellomycetaceae are a family of fungi in the Ascomycota, class Eurotiomycetes.
  • In brief, Eaparva, the type species of Emmonsia, was transferred to the genus Blastomyces (as Bparvus).
  • The genus Emmonsia was more narrowly defined to include Eacrescens and Easoli, the latter currently known only from soil.
  • A new genus, Emergomyces, was created to accommodate Emmonsia-like systemic dimorphic pathogens related to Espasteurianus (formerly Eapasteuriana) and characterized in the thermodependent phase by small yeast cells with narrow-based buds.
  • The earliest known isolate among these Emergomyces species was from 1992.

It remains unclear if these Emergomyces have truly emerged or whether they are only now recognized because of an increase in the number of susceptible hosts, improved microbiology capacity, and/or the widespread adoption of molecular identification techniques in clinical and research laboratories.

Source:

https://doi.org/10.1371/journal.ppat.1007977

https://languages.oup.com/google-dictionary-en/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4478585/

https://www.britannica.com/science/conidium

https://www.sciencedirect.com/science/article/pii/S1755001711000340

Untereiner WA, Scott JA, Naveau FA, Sigler L, Bachewich J, Angus A (2004). “The Ajellomycetaceae, a new family of vertebrate-associated Onygenales”Mycologia96 (4): 812–21. doi:10.2307/3762114JSTOR 3762114PMID 21148901. Retrieved 2010-01-04.


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Keywords: dimorphic fungus, fungal infection, what is Emergomyces, new fungal disease, emerging disease

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