Zygomycoses

Abstract Zygomycosis is a group of fungal infections caused by a variety of mould organisms belonging to the class Zygomycetes. This class is further classified into two orders, Mucorales and Entomophthorales. Fungi belonging to the order Mucorales are distributed into six families all of which can cause cutaneous and deep infections in immunocompromised patients (Ribes et al, 2000) (Fig. 15–1). In contrast, the order Entomophthorales contains two families of organisms that cause subcutaneous and mucocutaneous infections primarily in immunocompetent children (Richardson and Shankland, 1999; Sugar, 2000) (Fig. 15–1). For years, infections caused by the Zygomycetes class of fungi were described in the literature under the names phycomycosis or zygomycosis. The term phycomycosis is no longer used because the class Phycomycetes no longer exists. The use of the term zygomycosis is taxonomically correct to describe infections caused by organisms belonging to the order Mucorales or Entomophthorales. However, infections caused by organisms of the order Mucorales differ both clinically and pathologically from infections caused by organisms of the order Entomophthorales. Therefore, zygomycosis is too imprecise and vague to convey useful information to the clinician. We propose to use the term mucormycosis for infections caused by organisms belonging to the order Mucorales and entomophtho-ramycosis for infections caused by organisms of the order Entomophthorales. We discuss each of these types of infections separately. A variety of organisms has been implicated in mucormycosis. However, organisms belonging to the family Mucoraceae are isolated more frequently from patients with mucormycosis patients than any other family. Rhizopus oryzae (Rhizopus arrhizus) is the most common cause of infection followed by Rhizopus microsporus var. rhizopodiformis (Richardson and Shankland, 1999; Ribes et al, 2000). Other, less frequently isolated species of the Mucoraceae family that cause a similar spectrum of infections include Absidia corymbifera, Apophysomyces elegans, Mucor species, and Rhizomucor pusillus (Kwon-Chung and Bennett, 1992; Ribes et al, 2000). Other organisms such as Cunninghamella bertholletiae (in Cunninghamellaceae family) have been increasingly isolated from patients with pulmonary and disseminated mucormycosis (Kwon-Chung et al, 1975; Ventura et al, 1986; Cohen-Abbo et al, 1993; Kontoyianis et al, 1994). Additionally, Saksenaea vasiformis (in Saksenaceae family) has been reported as a cause of cutaneous (Bearer et al, 1994), subcutaneous (Pritchard et al, 1986; Lye et al, 1996), rhinocerebral (Gonis and Starr, 1997), and disseminated infections (Torell et al, 1981; Hay et al, 1983). Rare cases of mucormycosis have been reported due to Cokeromyces recurvatus (Kemna et al, 1994) (in Thamnidiaceae family), Mortierella species (Ribes et al, 2000) (in Mortierellaceae family) and Syncephalastrum species (Kamalam and Thambiah, 1980) (in Syncephalastraceae family).