VIII - EPIDEMIOLOGIC AND TAXONOMIC IMPACT OF PNEUMOCYSTIS BIODIVERSITY

A cluster of antigenic, genomic, karyotypic, isoenzymatic and morpholo gical differences have been reported among Pneumocystis populations, M ultilocus enzyme electrophoresis revealed strong linkage disequilibriu m suggesting that Pneumocystis genotypes from different hosts have bee n genetically isolated from each other for a very long time. At least in some cases, genetic diversity is associated with phenotypic differe nces as revealed by in vitro, ultrastructural and cross infection stud ies. Thus, biodiversity in Pneumocystis has obvious epidemiological im plications. Cross infection experiments revealed that Pneumocystis hos t species-related genetic differences are associated with close host s pecies specificity, which suggests that transmission cannot take place between hosts of different species and that immunocompromised patient s contract the infection primarily from infected humans. But these aff irmations do not preclude other reservoirs for human pneumocystosis an d research has to be extended to natural populations of synanthropic o r wild mammals. Transmission of human pneumocystosis was also approach ed by typing human Pneumocystis isolates from patients or carriers, wh ich should allow the follow up of parasite strains in human population s. As the strains of Pneumocystis found in different host species were considered for a long time to be morphologically indistinguishable, o nly one species of Pneumocystis was accepted for almost one century. A t present, the scientific community is progressively accepting that th e terminology 'P. carinii' is hiding a heterogeneous group of microorg anisms. As available data made it impossible to establish if genetic d ivergence derives from clonal reproduction or speciation, no new speci es names have been attributed to Pneumocystis populations, but a trino mial nomenclature, including the Latin name of the host, was adopted i n 1994. It has to be outlined finally that works on biodiversity of Pn eumocystis populations are basically important as they have revealed a new group of eukaryotic, pathogenic, heterogeneous microorganisms wit h fungal affinities, difficult to cultivate until now and widely sprea d in ecosystems. These researches are opening a virgin field for micro biology research. (C) 1998 Federation of European Microbiological Soci eties. Published by Elsevier Science B.V. All rights reserved.