Ere heart affectation [7,14?8] and digestive abnormalities, which are exceptional in northern South America and Central America [19,20]. TcIII which is usually isolated from vectors and sylvatic reservoirs has a low prevalence in human infections [11,21,22] whereas TcIV shows a similar geographical distribution but higher incidence in human infection [15,23?5]. Although sialic acid is crucial for the life cycle of T. cruzi, being involved in host cell adhesion/invasion processes and escape from the complement, the parasite is unable to synthesize this sugar de novo. To circumvent this gap, the parasite expresses the transsialidase (TS), that transfers a(2,3)-linked sialyl residues among glycoproteins or glycolipids. Circulating TS activity alters the sialylation pattern of the cellular glycoconjugates leading to hematological and immunological inhibitor abnormalities associated to the disease [26?8]. Genes encoding TS are included in a large family composed of at least 1439 members [29], a figure certainly underestimated due to the expected collapse when assembling closely similar sequences. Although several different groups of genes can be discerned, only 
one of them includes those that code for the TS proteins [30,31]. It has been estimated that as many as 150 genes of this group are included in the genome [32] where two TS isoforms, the active enzyme (aTS) and an enzymatically inactive TS (iTS) are encoded. Comparison of the aTS vs. iTS deduced amino acid sequences shows variations in 20 residues, although the inactivation is entirely due to the single crucial Tyr342His replacement as a consequence of a T/C transition [33]. The replacement by histidine renders the protein enzymatically inactive but allows retaining the substrate binding ability conferring therefore a lectinlike activity [32,34]. This strongly suggests a physiologic role for iTS in parasite attachment to substrates or cell surface receptors that might explain its conservation. Crystallographic analyses and enzyme kinetic assays [35] have recently shown that iTS retains residual hydrolytic activity. By using the recombinant iTS, a costimulating host T-cells effect have been adscribed [36]. Previous efforts to associate parasite Epigenetics genetic classification and biological features have allowed us to determine the expression/ shed of aTS as a marker of pathogenicity that segregates strains belonging to different lineages [37]. In this study our aim was to analyze the distribution of genes encoding the virulence factor TS among DTU-representative isolates collected along the Americas in the context of their evolution. We found aTS in all analyzed stocks and the striking absence of iTS genes in TcI, TcIII and TcIV DTUs. The consistence of the TS results with current T. cruzi evolutionary genome models was reviewed to fit findings. Parasite stocks to attempt genetic KO or to assay the involvement of iTS in parasite biology and virulence are now available.CBBcl2, ESMcl3Z2, IVVcl4, MAS1cl1, MVBcl8, X109/2, 3.1, 92122102R, STC10R, STC16Rcl1, MNcl2, SC43cl1, CA15, P63cl1 strains was obtained 16574785 from epimastigotes. The Blood and Cell Culture DNA Purification Kit (Qiagen) or conventional phenol-chloroform DNA extraction methods were used.DTU characterizationAll T. cruzi DNA samples were genotyped using polymerase chain reaction (PCR) strategies following Burgos et al [17] algorithm of classification. Some T. cruzi stocks (CID, H1, QUE, CBBcl2, ESMcl3Z2, IVVcl4, MAS1cl1, MVBcl8, X109/2, 3.1, 9212210.Ere heart affectation [7,14?8] and digestive abnormalities, which are exceptional in northern South America and Central America [19,20]. TcIII which is usually isolated from vectors and sylvatic reservoirs has a low prevalence in human infections [11,21,22] whereas TcIV shows a similar geographical distribution but higher incidence in human infection [15,23?5]. Although sialic acid is crucial for the life cycle of T. cruzi, being involved in host cell adhesion/invasion processes and escape from the complement, the parasite is unable to synthesize this sugar de novo. To circumvent this gap, the parasite expresses the transsialidase (TS), that transfers a(2,3)-linked sialyl residues among glycoproteins or glycolipids. Circulating TS activity alters the sialylation pattern of the cellular glycoconjugates leading to hematological and immunological abnormalities associated to the disease [26?8]. Genes encoding TS are included in a large family composed of at least 1439 members [29], a figure 
certainly underestimated due to the expected collapse when assembling closely similar sequences. Although several different groups of genes can be discerned, only one of them includes those that code for the TS proteins [30,31]. It has been estimated that as many as 150 genes of this group are included in the genome [32] where two TS isoforms, the active enzyme (aTS) and an enzymatically inactive TS (iTS) are encoded. Comparison of the aTS vs. iTS deduced amino acid sequences shows variations in 20 residues, although the inactivation is entirely due to the single crucial Tyr342His replacement as a consequence of a T/C transition [33]. The replacement by histidine renders the protein enzymatically inactive but allows retaining the substrate binding ability conferring therefore a lectinlike activity [32,34]. This strongly suggests a physiologic role for iTS in parasite attachment to substrates or cell surface receptors that might explain its conservation. Crystallographic analyses and enzyme kinetic assays [35] have recently shown that iTS retains residual hydrolytic activity. By using the recombinant iTS, a costimulating host T-cells effect have been adscribed [36]. Previous efforts to associate parasite genetic classification and biological features have allowed us to determine the expression/ shed of aTS as a marker of pathogenicity that segregates strains belonging to different lineages [37]. In this study our aim was to analyze the distribution of genes encoding the virulence factor TS among DTU-representative isolates collected along the Americas in the context of their evolution. We found aTS in all analyzed stocks and the striking absence of iTS genes in TcI, TcIII and TcIV DTUs. The consistence of the TS results with current T. cruzi evolutionary genome models was reviewed to fit findings. Parasite stocks to attempt genetic KO or to assay the involvement of iTS in parasite biology and virulence are now available.CBBcl2, ESMcl3Z2, IVVcl4, MAS1cl1, MVBcl8, X109/2, 3.1, 92122102R, STC10R, STC16Rcl1, MNcl2, SC43cl1, CA15, P63cl1 strains was obtained 16574785 from epimastigotes. The Blood and Cell Culture DNA Purification Kit (Qiagen) or conventional phenol-chloroform DNA extraction methods were used.DTU characterizationAll T. cruzi DNA samples were genotyped using polymerase chain reaction (PCR) strategies following Burgos et al [17] algorithm of classification. Some T. cruzi stocks (CID, H1, QUE, CBBcl2, ESMcl3Z2, IVVcl4, MAS1cl1, MVBcl8, X109/2, 3.1, 9212210.
