The causal agents of ‘entomophthoramycosis’ belong to two different orders: a suggestion for modification of the clinical nomenclature

Abstract

An interesting and comprehensive review ofmucormycosis and entomophthoramycosis inthe March 2004 supplement of Clinical Microbio-logy and Infection described the clinical manifesta-tions and treatments of mycosis caused by speciesof the Mucorales and Entomophthorales [1]. As inother recent reviews of zygomycosis [2,3], theauthors treat the two fungal genera Basidiobolusand Conidiobolus as both belonging to the orderEntomophthorales [1]. However, this should bemodified in accordance with more recent accep-ted knowledge about fungal taxonomy. Here, webriefly outline the recent status of medicallyrelevant fungi and suggest how this knowledgeshould be implemented in the clinical nomencla-ture.The ‘true’ fungi have been divided historicallyinto four phyla, the Ascomycota, Basidiomycota,Chytridiomycota and Zygomycota, based onmorphological and cytological characteristics[4]. However, while molecular analyses duringthe last two decades have supported the taxo-nomic status of the Ascomycota and Basidiomy-cota, orders within Chytridiomycota andZygomycota cluster between each other, andtherefore cannot be considered to be naturaltaxons [5–7]. One of the problematic orders ofthe Zygomycota is the Entomophthorales, whichcontains members found in two phylogeneticallydistinct groups, one of which contains Basidiobo-lus, which is related closely to some chytrids,while the remaining entomophthoralean genera,including Conidiobolus, form another distinctgroup that is related closely to other zygomycetessuch as Mucorales [6]. A further indication of aclose link between Basidiobolus and the flagellatedChytridiomycota is the presence of the procentri-ole, the basal part of a flagellum, in Basidiobolus[8]. This evidence has resulted in the delineationof the order Basidiobolales, containing the singlegenus Basidiobolus [9]. At present, available dataalso suggest that the pathogenic agents causingmucormycosis are all members of the Mucorales[10].The paraphyletic nature of the Entomophtho-rales, as defined previously, containing bothBasidiobolus and Conidiobolus, offers a partialexplanation of the highly different clinicalmanifestations of basidiobolomycosis and conid-iobolomycosis, and of their differences in suscep-tibility to antifungal agents [1,3,11]. Accordingly,a differentiation in the treatment strategies for thetwo mycoses, which until now have been uniform[1,3], deserves to be considered. Previousdifficulties with identification based on morpho-logical characteristics [1,3] can be overcome byprecise and quick identification of Conidiobolusand Basidiobolus using PCR with taxon-specificprimers [12]. We therefore recommend that theclinical nomenclature should reflect the modernphylogeny, and that the term ‘entomophthora-mycosis’ should be restricted to mycosis causedby Conidiobolus spp., while mycosis caused byBasidiobolus spp. should be described as‘basidiobolomycosis’.A. B. Jensen* and K. M. Dromph