Histopathology and Diagnosis
In the absence of specific antigen tests for A. crescens and relatives, and since the fungus cannot easily be cultured from respiratory secretions, the diagnosis of virtually all human and animal cases of adiaspiromycosis has relied on histopathological examination of biopsy or necropsy tissues (see, for example, Austwick 1968; Kodousek 1972; Nuorva et al.
1997; Simpson and Gavier-Wilden 2000; Moraes and Gomes 2004; Borman et al. 2009; Denson et al. 2009). Visualisation of adiaspores can be facilitated in fresh intact tissue by KOH digestion (Borman et al. 2009; Chantrey et al. 2006) and the formal identification of the etiological agent can be confirmed by PCR amplification and sequencing of fungal genomic DNA extracted from infected lung tissue (Borman et al. 2009; Dot et al. 2009). In severe animal infections in which adiaspore burdens are high, firm whitish nodules measuring several millimetres in diameter may be visible in the external lung parenchyma (Peres et al. 1992; England and Hochholzer 1993; Chantrey et al. 2006; Borman et al. 2009) (Fig. 7.1a, b). In fixed histopathological sections, individual giant adiaspores can be visualised as round to oval cells with a multi-laminar thick cell wall, and granular cytoplasmic contents (Fig. 7.1c). In human infections caused by A. crescens, reported adiaspore sizes vary quite widely (40-500 μm). Whether this is a function of the age of the infection (Anstead et al. 2012) or of different aetiology (Schwartz et al. 2015a) remains to be established. Typically, pulmonary adiaspores in immunocompetent hosts are surrounded by a dense granulomatous inflammatory infiltrate comprising macrophages, lymphocytes, scanty neutrophils together with epithelioid cells, multinucleate giant cells and fibromatous matter (Fig. 7.1c, d). Depending on section thickness and tissue integrity, it is not uncommon to see empty granulomata and granulomata with no central adiaspore in heavily infected lungs (Fig. 7.1c). Pulmonary functional compromise results from compression of smaller airways via tissue disruption due to the granulomata (Watts and Chandler 1975).Emergomycosis is diagnosed by culture of Emergomyces species from blood or biopsy material from skin or other affected tissues (Kenyon et al. 2014). The fungus usually grows on Sabouraud's agar within 2 weeks, though incubation up to 6 weeks at 30 °C is recommended. Yield from blood culture can be improved by use of mycobacterial/fungal blood culture bottles. Histopathological examination of skin tissue can secure the diagnosis of deep fungal infection with shorter turnaround time. Emergomyces species appear as small yeasts measuring 3-7 μm and cannot be distinguished from other dimorphic fungi with small yeasts (i.e. Histoplasma, Sporothrix, etc.) (Schwartz et al. 2015a).
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