Miscellaneous Fungi
Authors: Baddley John W , Dismukes William E 
Published: October 2023

Over the past decade, rare and unusual fungi, often common soil saprophytes, have been increasingly reported as causing invasive infections in humans. Possible reasons for an increased frequency of unusual fungal infections include increasing numbers of patients with immunosuppression, and increases in environmental exposures. This chapter focuses on unusual and rare yeast and mould organisms and their disease manifestations. Lobomycosis, a chronic skin infection caused by the yeast-like organism Lacazia loboi, is described, followed by infections due to basidiomycetes, and Emmonsia parva, the agent of adiaspiromycosis. Finally, rhinosporidiosis is discussed, although recent evidence indicates that the causative agent, Rhinosporidium seeberi, should no longer be classified as a fungus. Lobomycosis is a chronic skin infection characterized by nodules, plaques, and verrucoid or ulcerated lesions. The agent of lobomycosis, now referred to as Lacazia loboi (Taborda et al, 1999), is a yeast-like organism in tissues, and is primarily a human pathogen. Dolphins (Tursiops truncatus and Sotalia fluviatilis) are the only nonhuman hosts that acquire natural infection (Migaki et al, 1971; Dudok van Heel, 1977; Cowan, 1993). Lobomycosis occurs in tropical and subtropical forests, and has been reported in South, Central, and North America, and in Europe (Rodriquez-Toro, 1993). The majority of cases are from the Brazilian and Colombian Amazonian regions; only recently has a case from the United States been described (Burns et al, 2000). The natural habitat of L. loboi is unknown, and is difficult to investigate because the organism has never been isolated and cultured in vitro. Most infections occur on the skin in areas exposed to trauma, suggesting that the organism is present in soil or on vegetation (Rodriquez-Toro, 1993). An aquatic source is also likely, based on reported infections among dolphins (Migaki et al, 1971; Dudok van Heel, 1977; Cowan, 1993). Lobomycosis was reported initially in 1930 by the dermatologist Jorge Lobo (Lobo, 1931), who described a native of the Amazon Valley who had numerous plaques and nodules in the lumbo-sacral region. His disease had slowly progressed for 19 years. Based on clinical and histologic findings of the case, Lobo believed that the etiologic fungus was similar to Paracoccidioides brasiliensis, and referred to the infection as keloidal blastomycosis. Since the initial description of lobomycosis, greater than 300 human cases have been confirmed (Fuchs et al, 1990; Rodriguez-Toro, 1993). Lesions occur on cool, exposed areas such as the feet, legs, ears, arms, elbows, and less frequently the face. Lesions can be localized or disseminated throughout the skin, resulting from contiguous extension, autoinoculation, or lymphatic spread. A single case has been described which suggests visceral involvement (Monteiro-Gei, 1971). A patient with lobomycosis of the leg and knee for 47 years was found to have a presumed testicular tumor; however histopathology results showed granulomas with giant cells, and fungi consistent with lobomycosis. Lobomycosis usually begins as a well-circumscribed, indurated papule, and as the cutaneous disease progresses, the lesions enlarge and new lesions appear. Nodular lesions are most frequent, although macules, papules, plaques, ulcers, and verrucous lesions may be present (See Color Fig. 28–1 in separate color insert) (Rodriques-Toro, 1993). Generally, the disease is insidious, and may progess over a period of 50 or more years (Pradinaud, 1998).