Submitted to: Infection, Genetics and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 11, 2008
Publication Date: April 18, 2008
Citation: Rosenthal, B.M., Dunams, D.B., Pritt, B. 2008. Restricted genetic diversity in the ubiquitous cattle parasite, sarcocystis cruzi. Infection, Genetics and Evolution.(5):588-592.
Interpretive Summary: A survey of a parasite that cycles between cattle and dogs have remarkably little genetic variability, when compared either to related parasites in other bovids or in wildlife hosts. North and South American isolates of this parasite seem not to have evolved distinct versions of a variable gene, suggesting that their residency in the Hemisphere may date only to the importation of domesticated dogs and/or cattle from Europe. Thus, humans may have played an important role in disseminating this parasite which, though incapable of infecting humans, infects nearly all cattle.
Although parasites of the genus Sarcocystis may have cycled between bovine herbivores and canine carnivores for tens of millions of years, human beings may have profoundly influenced the ecology and evolution of those parasites prevalent in domesticated dogs and cattle. To preliminarily assess the possibility of such anthropogenic effects, we surveyed genetic variation in conserved and variable portions of ribosomal DNA from a large sample of Sarcocystis cruzi occurring in taurine beef cattle raised in the United States and Argentina, and compared these data to available homologues, including those reported from zebu cattle, water buffalo, and bison. For additional context, we compared the apparent diversity of cattle parasites to that reported from congeneric parasite species in other hosts. We find that the parasites of taurine cattle, whether derived from the Americas or Asia, are completely lacking in variability at the small subunit rDNA. By contrast, geographically limited samples of related wildlife parasites are more variable. At the adjacent ITS-1 locus, allelic distributions suggest that the parasite may have been introduced to the Americas via domesticated dogs or cattle. Thus, human impact on this parasite's distribution and diversification would seem to have been great.