Unusual Fungal and Pseudofungal Infections of Humans

The spectrum of mycotic disease continues to expand well beyond the familiar entities of candidiasis and aspergillosis (73, 99). The field of medical mycology has become a challenging study of infections caused by a wide and taxonomically diverse array of opportunistic fungi (73). Previously we reviewed some of the less-common “emerging” opportunistic fungal pathogens with an emphasis on resistance to new and established antifungal therapies (73). In this article, we discuss several exotic and unusual infections that historically have been considered fungal or pseudofungal infections based on their clinical and histopathologic presentation but have been difficult to classify because they grow poorly or not at all on artificial media. In one instance, recent molecular evidence has indicated that an organism previously considered to be a fungus (Rhinosporidium seeberi) is in fact a protistan parasite (29, 37). We also discuss a nonreplicative pulmonary infection (adiaspiromycosis), two subcutaneous mycoses (entomophthoromycosis and lobomycosis), two algal infections (chlorellosis and protothecosis), and an infection due to the oomycete Pythium insidiosum. The diagnosis of these rare infections is based largely on detection of characteristic structures observed on histopathologic examination of tissue. A listing of the infections, the etiologic agents, and the typical morphology in tissue is provided in Table 1 and Fig. 1 and 2 .