A new consensus for Trypanosoma cruzi intraspecific nomenclature : second revision meeting recommends TcI to TcVI

1Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, São Paulo, SP, Brasil 2Centro de Pesquisas Gonçalo Moniz, Fundação Oswaldo Cruz-Fiocruz, Salvador, BA, Brasil 3Departamento de Microbiologia, Imunologia e Parasitologia, Universidade Federal de São Paulo, São Paulo, SP, Brasil 4Department of Microbiology, Immunology and Molecular Genetics, David Geffen School of Medicine, University of California, Los Angeles, CA, USA 5Departamento de Parasitologia 9Departamento de Bioquímica e Imunologia, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brasil 6Laboratório Interdisciplinar de Pesquisas Médicas, Instituto Oswaldo Cruz-Fiocruz, Rio de Janeiro, RJ, Brasil 7Centro de Investigaciones en Microbiología y Parasitología Tropical, Facultad de Ciencias, Departamento de Ciencias Biológicas, Universidad de los Andes, Bogotá, Colombia 8Departamento de Ciências Biológicas, Universidade Federal do Triângulo Mineiro, Uberaba, MG, Brasil 10Pathogen Molecular Biology Unit, London School of Hygiene and Tropical Medicine, London, UK 11Instituto de Pesquisas René Rachou-Fiocruz, Belo Horizonte, MG, Brasil 12Laboratory of Genetics and Evolution of Infectious Diseases, UMR IRD/CNRS 2724, Montpellier, France 13Laboratorio de Biología Molecular de la Enfermedad de Chagas, Instituto de Ingeniería Genética y Biología Molecular, CONICET, Buenos Aires, Argentina

The biological, biochemical and genetic diversity of Trypanosoma cruzi strains has long been recognised, along with their eco-epidemiological complexity, which has been reviewed extensively elsewhere (Macedo & Pena 1998, Campbell et al. 2004). Over the years, numerous approaches have been used to characterise the population structure of T. cruzi, aiming at defining the number of relevant subgroups. Accordingly, these subgroups received different designations, including zymodemes (Miles et al. 1977, 1978, 1981, Romanha et al. 1979, schizodemes (Morel et al. 1980), biodemes (Andrade 1974, Andrade & Magalhães 1997, clonets (Tibayrenc & Ayala 1991), lineages (Souto et al. 1996), clades (Kawashita et al. 2001) and, more recently, discrete typing units (DTUs) (Tibayrenc 1998) and haplotypes (Freitas et al. 2006, Herrera et al. 2007. In a Satellite Meeting held at Fiocruz in 1999, an expert committee reviewed the available knowledge that indicated a convergence toward clustering T. cruzi strains into two major groups. Recommendations were issued that can be summarised as follows (Anonymous 1999). T. cruzi strains characterised by biological and biochemical features (e.g., biodemes and zymodemes) and molecu-lar techniques [e.g., multilocus enzyme electrophoresis (MLEE), random amplification of polymorphic DNA (RAPD), mini-exon and 24Sα ribosomal DNA sequences] should be classified into two principal groups, named T. cruzi I and T. cruzi II. The classification of apparent hybrid strains and strains equivalent to Zymodeme 3 (Miles et al. 1978(Miles et al. , 1981 and Biodeme Type I (Andrade 1974) would be decided later after further studies.
In the 10 years that followed the meeting at Fiocruz, the scientific community has advanced in the knowledge of T. cruzi diversity. Multilocus genotyping has revealed six distinct DTUs, which partition into two major subdivisions, termed DTU I and DTU II. DTUs are defined as ''sets of stocks that are genetically more related to each other than to any other stock and that are identifiable by common genetic, molecular or immunological markers'' (Tibayrenc 1998). T. cruzi DTU II was further split into five DTUs, IIa-e (Brisse et al. 2000(Brisse et al. , 2001, based on congruent phylogenetic information from MLEE and RAPD markers. DTUs I and IIb correspond, respectively, to the T. cruzi I and T. cruzi II groups recommended by the original expert committee in 1999 (Table I). Current studies indicate that four subdivisions have emerged within DTU I as well (Herrera et al. 2007, Falla et al. 2009), although these have not been integrated into the nomenclature revision.
Although the major genetic variability of T. cruzi was proposed initially to have resulted from predominant clonal evolution (Tibayrenc et al. 1986), increasing evidence indicates that genetic exchange between parasites has contributed to the present popu-lation structure (Sturm & Campbell 2009). This was first documented by the existence of hybrid organisms in sylvatic T. cruzi populations and sympatric clinical strains and, later, experimentally (Gaunt et al. 2003 and cited references). The prevailing view is that DTU I and DTU IIb are ancient lineages and that DTU IId and DTU IIe strains are the products of a minimum of two hybridisation events (Westenberger et al. 2005, Freitas et al. 2006, Tomazi et al. 2009). The evolution of DTU IIa and DTU IIc strains is insufficiently understood for the moment, although these DTUs may also have a hybrid origin (Sturm et al. 2003, Westenberger et al. 2005. Based on microsatellite and mitochondrial DNA analyses, DTU IIc may represent a third ancestral lineage, which was named T. cruzi III (Freitas et al. 2006).
The advances in the understanding of T. cruzi population structure indicate that it is time to revise the nomenclature of T. cruzi strains. The standardisation of nomenclature will facilitate communication among researchers working with T. cruzi aimed at characterisation of its eco-epidemiological features, pathogenicity and questions of basic biology. By consensus, the expert committee recognised that the nomenclature for T. cruzi strains should be classified into six DTUs, T. cruzi I-VI and issued recommendations accordingly. Detailed justification and implications of these decisions will be presented in a future publication.

Recommendations of the Second Satellite Meeting -(i)
The known isolates and strains of T. cruzi should be assigned to one of six DTUs (T. cruzi I-VI). Additional variants may arise in the future; (ii) DTUs T. cruzi I and T. cruzi II correspond to the two groups originally defined in the First Satellite Meeting (Anonymous 1999). A notable exception is the CL Brener strain, classified at that time as T. cruzi II and now reclassified as T. cruzi VI; (iii) The designation of the six DTUs, their abbreviations and equivalence are summarised in Table I Falla et al. 2009;c: Brisse et al. 2000;d: Miles et al. 1981; DTU: discrete typing units; e: Mendonça et al. 2002;f:Freitas et al. 2006;g: Souto et al. 1996;h: Tibayrenc and Ayala 1991;i: Chapman et al. 1984 ;j: Carneiro et al. 1990. entific journals are encouraged to adopt the recommended nomenclature for the T. cruzi DTUs in their journals; (vi) Typing services should be made available for strains in the existing literature. A list of some reference and "experimental" strains and their corresponding designation is presented to serve as guide for researchers (Table II).
To obtain the greatest effectiveness, the new recommendations for the naming of T. cruzi will require a simple and reproducible schema for typing isolates into their respective DTUs. Lewis et al. (2009) described such a schema using currently available markers in the form of a triple assay that employed rDNA PCR (Souto et al. 1996) and PCR-RFLP of the HSP60 and GPI loci (Westenberger et al. 2005). The expert committee is exploring the possibility of a multicentric study to standardise and validate different protocols for genotyping reference and laboratory strains, as well as field isolates. Any multicentric study will make a call for comparative typing protocols that are under development currently in other laboratories.