Abstract
Trypanosoma cruzi, the causative agent of Chagas disease, is a multiclonal parasite with high levels of genetic diversity and broad host and geographic ranges. Molecular characterization of South American isolates of T. cruzi has demonstrated homologous recombination and nuclear hybridization, as well as the presence of 6 main genetic clusters or “discrete typing units” (DTUs). Few studies have extensively investigated such exchange events and genetic diversity in North American isolates. In the current study, we genetically characterized over 50 US isolates from wildlife reservoirs (e.g., raccoons, opossums, armadillos, skunks), domestic dogs, humans, nonhuman primates, and reduviid vectors from nine states (TX, CA, OK, SC, FL, GA, MD, LA, TN) using a multilocus sequencing method. Single nucleotide polymorphisms were identified in sequences of the mismatch-repair class 2 (MSH2) and Tc52 genes. Typing based on the two genes often paralleled genotyping by classic methodologies using mini-exon and 18S and 24Sα rRNA genes. Evidence for genetic exchange was obtained by comparing sequence phylogenies of nuclear and mitochondrial gene targets, dihydrofolate reductase-thymidylate synthase (DHFR-TS) and the cytochrome oxidase subunit II- NADH dehydrogenase subunit I region (COII-ND1), respectively. We observed genetic exchange in several US isolates as demonstrated by incongruent mitochondrial and nuclear genes phylogenies, which confirms a previous finding of a single genetic exchange event in a Florida isolate. The presence of SNPs and evidence of genetic exchange illustrates that strains from the US are genetically diverse, even though only two phylogenetic lineages have been identified in this region.
Highlights
Trypanosoma cruzi, the causative agent of Chagas disease, is a clonally proliferative parasite with a heterogeneous population [1,2]
Based on mismatch-repair class 2 (MSH2), Tc52, and dihydrofolate reductasethymidylate synthase (DHFR-TS) sequences, all human (TcI), ring-tailed lemurs (TcIV), armadillo (TcI or TcIV) and skunk (TcIV) isolates were genotyped as the equivalent lineages previously determined [34]
Single nucleotide polymorphisms (SNPs) were observed in the MSH2 and Tc52 genes of the analyzed sequences compared to TcI and TcIV reference strains from South America (Tables 2 and 3)
Summary
Trypanosoma cruzi, the causative agent of Chagas disease, is a clonally proliferative parasite with a heterogeneous population [1,2]. It is a biologically, molecularly, and biochemically diverse parasite that has been detected in over 200 mammalian species, including humans [3]. Prior to advances in molecular biology and genetics, differences in T. cruzi were based solely on growth characteristics and manifestations of disease in various hosts [4]. Characterizing a strain of T. cruzi into one of these six genotypes is useful in determining the evolutionary ecology of the parasite in a region, as well as, associating biological characters with disease manifestations. A predominately clonal population structure for T. cruzi was accepted [9], but with recent evidence for genetic exchange events, hybridization, and mitochondrial introgression this model has been challenged [10,11,12,13,14,15,16,17]
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