Taxonomy of Trypanosoma cruzi: a commentary on characterization and nomenclature.

Early in the history of Chagas disease it became apparent that there was considerable variation in the incidence and severity of infections with parasites classified as being Trypanosoma cruzi (see Pessoa 1960 for a review of early findings by scientists such as Carlos Chagas and Emmanuel Dias). A variety of typing schemes were developed as a means of finding the basis of this variation and more finely, classifying the organisms within the species. Here instead of reviewing the literature on this topic a critical perspective on the typing of T. cruzi is presented. Early attempts at typing strains included the immunological types of Nussensweig et al. (1963) however it was the pioneering work of Andrade (1974) who first correlated specific arrays of morphobiological and behavioural characters to particular types within T. cruzi. The molecular typing of T. cruzi strains was pioneered with isoenzymes (Toye 1974) and Miles used the technique to classify isolates of this parasite into strain-groups (Miles et al. 1977) and types (Miles et al. 1978). The term zymodeme was later introduced (Barrett et al. 1980) to refer to “trypanosome populations that possess like forms of specified enzymes”. Ready and Miles (1980) suggested that the T. cruzi zymodemes indicated distinct taxa, however, Miles et al. (1981a, b) were reluctant to give the taxa subspecific status. This reluctance was followed by nearly all subsequent authors, eventhough the basic zymodeme divisions were confirmed by many subsequent studies using a variety of techniques at both the protein and DNA level (Table) and a strong correlation between the intrinsic and extrinsic characters (Lumsden 1977) of T. cruzi types was convincingly demonstrated (Andrade et al. 1983, Andrade 1985). RELUCTANCE TO NAME FORMAL TAXA