Emergomyces
The genus, Emergomyces, has recently been created to accommodate a number of novel dimorphic human pathogens that had previously been described in the genus Emmonsia.
Five species are recognised: Emergomyces pasteurianus, E. africanus, E. orientalis, E. canadensis and E. europaeus (Dukik et al., 2017; Wang et al., 2017; Jiang et al., 2018; Schwartz et al., 2019). A review of the genus was provided by Samaddar and Sharma (2021).
Almost all reported cases of Emergomyces infection (emergomycosis) have occurred in HIV-infected individuals, often presenting as disseminated disease with cutaneous lesions. Note: Clinical features mimic those of histoplasmosis. To date, Emergomyces infections have been reported from four continents: Asia, Africa, Europe and North America. The most extensive burden of disease has been observed among HIV-infected patients from South Africa attributed to E. africanus (Moodley et al., 2019).
RG-2 organism.
Morphological genus description: Emergomyces species exhibit thermal dimorphism growing in living tissue or in culture at 37oC as a budding yeast-like fungus and in culture at temperatures below 30oC as a mould. Colonies at 25oC are slow growing, yellowish-white to tan, initially glabrous, becoming powdery, with a pale yellow reverse. Conidia are borne on slender stalks alongside hyphae or in groups on inflated cells. They are small, thin-walled, one-celled, sub-globose, and 2-4 µm in diameter. Colonies at 37°C on brain heart infusion (BHI) agar containing blood are moist, white to cream coloured and yeast-like. Microscopically, numerous small, oval shaped, narrow based budding yeast-like cells, 2-5 µm in size are observed. Note:Histopathological features of emergomycosis also mimic histoplasmosis. In fact, these infections are indistinguishable from one another, both showing intracellular narrow based budding yeasts, measuring 2-5 µm in size.
Molecular identification: ITS sequencing is necessary for accurate identification of species (Jiang et al., 2018; Samaddar and Sharma, 2021).
Key features: Clinical history, tissue morphology culture identification by ITS sequencing.
Antifungal Susceptibility: Emergomyces africanus (Maphanga et al., 2017); MIC µg/mL.
| Antifungal | Mould form | Yeast form | ||
| Range | MIC90 | Range | MIC90 | |
| AMB | ≤0.008-1 | 0.25 | ≤0.008-1 | 0.25 |
| FLU | 0.125-8 | 0.5 | 0.125-1 | 0.5 |
| ITRA | 0.008-0.5 | 0.06 | 0.008-0.125 | 0.008 |
| VORI | 0.008-0.06 | 0.03 | 0.008-0.015 | 0.015 |
| POSA | 0.008-1 | 0.06 | 0.008-0.25 | 0.03 |
References: Kenyon et al. (2013); Dukik et al. (2017); Wang et al. (2017); Jiang et al. (2018); Schwartz et al. (2018a,b; 2019); Samaddar and Sharma (2021).