The ancient and divergent origins of the human pathogenic trypanosomes, Trypanosoma brucei and T. cruzi

Abstract

This study presents new findings concerning the evolution of the human pathogens, Trypanosoma brucei and T. cruzi, which suggest that these parasites have divergent origins and fundamentally different patterns of evolution. Phylogenetic analysis of 18S rRNA sequences places T. brucei in a clade comprising exclusively mammalian trypanosomes of African origin, suggesting an evolutionary history confined to Africa. T. cruzi (from humans and sylvatic mammals) clusters with trypanosomes specific to Old and New World bats, T. rangeli and a trypanosome species isolated from an Australian kangaroo. The origins of parasites within this clade, other than some of those from bats, lie in South America and Australia suggesting an ancient southern super-continent origin for T. cruzi, possibly in marsupials; the only trypanosomes from this clade to have spread to the Old World are those infecting bats, doubtless by virtue of the mobility of their hosts. Viewed in the context of palaeogeographical evidence, the results date the divergence of T. brucei and T. cruzi to the mid-Cretaceous, around 100 million years before present, following the separation of Africa, South America and Euramerica. The inclusion in this study of a broad range of trypanosome species from various different hosts has allowed long phylogenetic branches to be resolved, overcoming the limitations of many previous studies. Moreover, T. brucei and the other mammalian tsetse-transmitted trypanosomes appear, from these data, to be evolving several times faster than T. cruzi and its relatives.

Kinetoplastid phylogenetics, with special reference to the evolution of parasitic trypanosomes

“…E-mail: j.r.stevens@ex.ac.uk 2000) and even in those parasites of medical importance, it is little more than a decade since the widespread introduction of DNA sequencing technologies has allowed the evolution of parasitic trypanosomatids (and kinetoplastids in general) to be evaluated by formal phylogenetic analysis (Fernandes et al, 1993;Alvarez et al, 1996;Maslov et al, 1996;Lukes et al, 1997;Haag et al, 1998;Hannaert et al, 1998;Stevens et al, 1999Stevens et al, , 2001Wright et al, 1999;Hamilton et al, 2004;Moreira et al, 2004). To fully understand the evolutionary history of parasitic kinetoplastids and to understand the context within which the evolution of each parasite group has unfolded, an understanding not just of the parasites, but also of broader kinetoplastid phylogenetics is required.…”

“…Although we have no evidence whether the ancestor of the 'aquatic clade' trypanosomes was leech or insect-transmitted, as suggested by Maslov et al (1996) it is clear that the majority of insect-transmitted trypanosomes did not evolve from this clade. Stevens et al (1999) and is based on an alignment of 1809 nucleotide positions. The phylogeny contains 61 Trypanosoma taxa and shows the genus to be monophyletic.…”

“…The phylogeny contains 61 Trypanosoma taxa and shows the genus to be monophyletic. T. congolense subgroups are denoted by s = savannah, f = forest, k = kilifi and t = tsavo; sequence accession numbers are given in Haag et al (1998) and Stevens et al (1999Stevens et al ( , 2001). Analysis was perfomed using PAUP* 4 (Swofford, 1998).…”

“…A monophyletic group consists of taxa that are descended from a single common ancestor and contains all known descendants from that ancestor. The first molecular phylogenetic studies, based on comparisons of mitochondrial and nuclear ribosomal DNAs (rDNA), showed trypanosomes to be paraphyletic (Gomez et al, 1991;Fernandes et al, 1993;Maslov et al, 1996), while subsequent rDNA-based studies, which have included more taxa from a far broader range of host species (Lukes et al, 1997;Stevens et al, 1999Stevens et al, , 2001Wright et al, 1999;Simpson et al, 2002;Hamilton et al, 2004) (Fig. 2) supported monophyly.…”

Ecological host fitting of Trypanosoma cruzi TcI in Bolivia: mosaic population structure, hybridization and a role for humans in Andean parasite dispersal

“…2011), and as such, it is characterized by considerable genetic diversity (Stevens et al . 1999). Current international consensus recognizes a minimum of six stable genetic lineages or discrete typing units (DTUs) (TcI‐TcVI) (Zingales et al .…”