Taxonomy of Trypanosoma cruzi: a Commentary on Characterization and Nomenclature


*Taxonomy of Trypanosoma cruzi:* a Commentary on Characterization and Nomenclature** From : Memorias do Instituto Oswaldo Cruz, Vol. 94, Suppl. I : 181-184 (1999) Hooman Momen Departamento de Bioquímica e Biologia Molecular, Instituto Oswaldo Cruz, Av. Brasil 4365, 21045-900 Rio de Janeiro, RJ, Brasil Key words: Trypanosoma cruzi - taxonomy - characterization - 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 sub-specific 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 PRIMARY PHYLOGENETIC DIVISIONS FINAL COMMENTS In the history of Chagas disease, the wheel has been reinvented many times (Dvorak 1984). A sound taxonomy may often have avoided much wasted time and effort. The third class of nomenclature as proposed by Lumsden (1977) has been usefully applied to T. cruzi (as shown in Table) however it may be time to consider the use of formal Linnean designations for the divisions within this parasite. Among the arguments used against the naming of T. cruzi taxa have been the presence of putative hybrids between the two main lineages of T. cruzi (major clone 39 and its equivalents); the need for further studies on the population structure as there is evidence of genetic recombination (Bogliolo et al. 1996, Carrasco et al. 1996); the difficulty of correlating strains with patient morbidity and the genetic variability of T. cruzi clones. The arguments against the formal naming of T. cruzi taxa though valid are disputed and in any case are not particular to this parasite and have not impeded the naming of taxa in other organisms. The present situation is similar to the early 80´s where the work of Miles et al. (1977, 1978) and Andrade (1974) had laid the basis for the formal naming of T. cruzi taxa. Again the strong correlations between major phylogenetic divisions in T. cruzi and biological characters (Andrade & Magalhaes 1997, Revollo et al. 1998) are being emphasized. The naming of species for the principal divisions and subspecies for the lower divisions would clearly aid in the comprehension of studies on this parasite. As pointed out by Steel (1962) "nomenclature should be our servant and not our master". REFERENCES TABLE