Making Moulds Meet Information Retrieval As a Basis for Understanding Pseudallescheria and Scedosporium

Research on orphan diseases has been boosted enormously over the last decade with the event of electronic communication. This has enabled the implementation of international networks providing research groups with sufficient critical mass for epidemiological studies. An example of such a success story is without doubt the knowledge on Scedosporium and its teleomorph Pseudallescheria. Although already known from human infections since the late 19th century, these fungi had long been regarded either as clinically insignificant, or as anecdotal. Today the species are listed among the major groups of filamentous opportunists.1,2 First attempts to unite researchers and clinicians were made by the Spanish Study Group on Scedosporium prolificans. In 2002, a Europe-wide group was founded under the umbrella of the European Confederation of Medical Mycology (ECMM). As similar initiatives were undertaken in Australia by the Australian Scedosporium Study Group (AUSCEDO), the two groups were internationalized under the auspices of the International Society of Human and Animal Mycology (ISHAM). Main objective of the Working Group Pseudallescheria/Scedosporium Infections was to gain insight into the epidemiology and genetic variability of these fungi and to provide data on possible sources of contamination and routes of infection. The taxonomy of the fungi had been revolutionised by the application of molecular methods, particularly through the papers of Gilgado et al.[3–5] The classical species Pseudallescheria boydii was subdivided into numerous species, several of which were indistinguishable by phenotypic characteristics that had been in use until recently. A complicating factor is the different degree of inbreeding and clonality between species, leaving doubt whether all genealogically separated entities can be referred to as species in the classical sense.6 In addition, it remains questionable whether distinction of all entities is clinically meaningful. But at least there is a wide consensus that Pseudallescheria is a species complex rather than a single species. Species have limited molecular heterogeneity and comprise limited numbers of haplotypes. A number of molecular techniques for diagnostics and detection are currently being developed using genes that have been suitable for identification of species. The widely used rDNA internal transcribed spacer (ITS) region of rDNA is suitable for the majority of clearly distinct taxa,7,8 whereas molecular siblings are separable by different loci in the β-tubulin gene.3,4 Scedosporium species are opportunists and thus understanding of their behaviour in human tissue can be reached only via knowledge of their environmental habitat. Kaltseis et al. [9] noted that Scedosporium species are positively associated with human-derived, industrial and agricultural pollution. Comparing the frequency of species from the environment with the distribution of species involved in human infection, the authors supposed significant difference in virulence between species. Virulence is concentrated in two locations in the phylogeny of Microascales with Scedosporium-like appearance, viz. in the Pseudallescheria boydii complex discussed above, and in Scedosporium prolificans.10 These fungi primarily cause subcutaneous infections in healthy individuals, or deep, occasionally disseminated infections in debilitated patients. A remarkable, newly recognised clinical syndrome is the near-drowning encephalitis, a delayed infection of the brain after aspiration of polluted water resulting in temporary coma.11,12 With improved isolation and detection techniques13–16Scedosporium species have also become recognised as common colonisers of the airways of patients with cystic fibrosis.17 The direct clinical significance of this finding is still unclear,18 but infection may be regarded as a contraindication for lung transplantation,19,20 the ultimate therapy for CF patients. Scedosporium infections are notoriously difficult to treat due to their limited susceptibility to most commonly used systemic antifungals. Species share this property with the Scopulariopsis agents of cutaneous infections, which belong to the same order, Microascales. In the filamentous ascomycetes such recalcitrance to therapy is matched only by the order Hypocreales, containing the genera Acremonium, Fusarium and Trichoderma. Scedosporium prolificans belongs to the fungi with the highest degree of resistance to antifungals known. Reasonable results have been obtained with combination therapy using voriconazole and terbinafin,21,22 but in general mortality rates in disseminated infections by this fungus rise until up to 87.5%.23 Infections caused by species of the P. boydii complex have proved less difficult to treat, with voriconazole being the drug of choice.24,25 Strains are currently identifiable with the sequence base available at http://www.scedosporium-ecmm.com. Species concepts applied in this database have been verified by multilocus analysis including several gene loci (ITS, BT2, TUB) and AFLP profiles, and taxonomy has been anchored by the inclusion of type strains. The database is divided up between clinical and environmental strains (Fig. 1) because metadata for the two categories are very different, but the identification procedure is identical. ITS and the BT2 and TUB loci of β-tubulin are sufficient for reliable identification. At the University of Sydney Westmead Hospital, a database for multilocus sequence typing applying six genetic loci for Scedosporium aurantiacum was developed and is accessible at http://mlst.mycologylab.org (A. Harun & W. Meyer, unpublished data). Clinical data are automatically transmitted to the Fungiscope database, where tools for epidemiological analysis are being installed. Deposition of live material is recommended in one of the recognised culture collections joining the project (Fig. 1), whereby the Belgian Coordinated Collection of Microorganisms at the Scientific Institute of Public Health (Brussels) serves as a prime depository for environmental strains. Strains are available to members of the Working Group if permission from the depositor is granted. A taxonomic database is available through MycoBank (http://www.mycobank.org), while a nearly complete collection of clinical papers published before 2006 is available on the ISHAM website (http://www.isham.org). Note that there is no link to GenBank, as this database is not updated according to taxonomic developments and sequences are not verified with ex-type materials. Flow diagram of data storage of clinical and environmental strains. The cooperating Working Groups have thus provided a basic infrastructure that is essential for the growth of knowledge on Pseudallescheria and Scedosporium. We offer access to a broad range of information on these emerging fungal opportunists, which should lead to appropriate and effective therapy. Clearly, the success of this endeavour depends on the ongoing activity of its supporters. Readers of this special issue are cordially invited to contribute to the network. The present special issue stems from presentations given at the PSI workshop held in Bonn, Germany, 6−8 May, 2010. The authors have no conflict of interests to declare.