Systemic zygomycosis.

Two families of the class of fungi known as Zygomycetes contain most of those members which are reported to cause human disease. The Entomophthoraceae are particularly associated with infection of the skin and subcutaneous tissue, whereas the Mucoraceae typically cause systemic disease. The species most often associated with such systemic infections include Rhizopus oryzae, Rhizopus rhizopodiformis, Absidia corymbifera and Rhizomucor pusillus; a number of other species are also occasionally implicated (Scholer et al., 1983), and it is clear that the number of identified pathogenic species is increasing. In clinical nomenclature, there is a terminological quagmire, within which 'mucormycosis', 'phycomycosis' and 'zygomycosis' are sometimes used as if they were synonymous (Medical Research Council, 1977). 'Phycomycosis' appears to have been rendered obsolete by taxonomic changes (Ajello et al., 1976; Emmons et al., 1977), though it was the term preferred by the nomenclature committees of the British Society for Mycopathology (Medical Research Council, 1977) and the International Society for Human and Animal Mycology (Vanbreuseghem et al., 1980), as well as the authors of a standard text in mycology (Emmons et al., 1977). Other major texts, however, prefer 'mucormycosis' (Rippon, 1982) or 'zygomycosis' (Chandler et al., 1980). The organisms causing cutaneous and subcutaneous infections can often be identified by culture, and it may then be logical to refer to the resulting clinical condition as 'entomophthoramycosis' or 'basidiobolomycosis'. 'Mucormycosis' should strictly be limited to cases proven by culture to be caused by a member of the Mucorales (Meyers et al., 1979; Hawksworth et al., 1983), but the term is established by long usage, and is customary where a diagnosis by biopsy only is available. This usage is potentially misleading, for zygomycetes not within the order of Mucorales can cause systemic zygomycosis (King & Jong, 1976; de Aguiar et al., 1980; Scholer et al., 1983). Deep infection is often only diagnosed on histological examination: the species cannot then be identified by any method in general use, and the genus can only be guessed at. It is, in such circumstances, not possible to be sure of anything other than that a zygomycete is present, and so the term 'zygomycosis' is safest. When a suitable adjective, such as 'systemic' or 'subcutaneous' is appended, all examples can be unambiguously labelled (Ajello et al., 1976). The Zygomycetes are typically found in soil and dung (Emmons, 1962). Members of the genera associated with human disease are part of the soil mycoflora in many parts of the world (Warcup, 1951; Miller et al., 1957; Moubasher & Abdel-Hafez, 1978), including the United Kingdom (Warcup, 1951; Nichols, 1956); they are frequent contaminants of animal fodder (Ainsworth & Austwick, 1955) and of tobacco (Papavassiliou et al., 1971). Their spores are widespread in the air (Agarwal et al., 1969; Hudson, 1973; Sorensen et al., 1974), are present in house dust (Davies, 1960) and were found in the atmosphere in a ward in a London teaching hospital (Noble& Clayton, 1963). They may be cultured from the sputum of a minority of healthy men (Kahanpiiii, 1972; Comstock et al., 1974). Pathogenic species were found in the warm effluent from a power station and in the soil of the immediate vicinity, though no significant associated increase in the air spore count could be detected (Rippon et al., 1980). Zygomycetes do not often cause human disease; their most common effects on our lives result from their ability to cause decay in many kinds of fruit and vegetables (Harter & Weimer, 1922). They are facultative necrotrophs, able to invade and kill living tissue, and to then withdraw nutrients from it (Cooke, 1977). They require previous damage to the skin of most fruits, either by trauma (Harter & Weimer, 1922) or initial attack by another agent (Stevens, 1914), before they can invade. Intact peach