title: Genetic characterization of Theileria equi infecting horses in North America: evidence for a limited source of U.S. introductions.
abstract: BACKGROUND
  Theileria equi is a tick-borne apicomplexan hemoparasite that causes equine piroplasmosis. This parasite has a worldwide distribution but the United States was considered to be free of this disease until recently.
  
  
  METHODS
  We used samples from 37 horses to determine genetic relationships among North American T. equi using the 18S rRNA gene and microsatellites. We developed a DNA fingerprinting panel of 18 microsatellite markers using the first complete genome sequence of T. equi.
  
  
  RESULTS
  A maximum parsimony analysis of 18S rRNA sequences grouped the samples into two major clades. The first clade (n = 36) revealed a high degree of nucleotide similarity in U.S. T. equi, with just 0-2 single nucleotide polymorphisms (SNPs) among samples. The remaining sample fell into a second clade that was genetically divergent (48 SNPs) from the other U.S. samples. This sample was collected at the Texas border, but may have originated in Mexico. We genotyped T. equi from the U.S. using microsatellite markers and found a moderate amount of genetic diversity (2-8 alleles per locus). The field samples were mostly from a 2009 Texas outbreak (n = 22) although samples from five other states were also included in this study. Using Weir and Cockerham's FST estimator (θ) we found strong population differentiation of the Texas and Georgia subpopulations (θ = 0.414), which was supported by a neighbor-joining tree created with predominant single haplotypes. Single-clone infections were found in 27 of the 37 samples (73%), allowing us to identify 15 unique genotypes.
  
  
  CONCLUSIONS
  The placement of most T. equi into one monophyletic clade by 18S is suggestive of a limited source of introduction into the U.S. When applied to a broader cross section of worldwide samples, these molecular tools should improve source tracking of T. equi outbreaks and may help prevent the spread of this tick-borne parasite.
authors: Center for Microbial Genetics and Genomics, Northern Arizona University, Flagstaff, AZ 86011, USA.
authors: Carina M
authors: CM
authors: Hall
authors: Joseph D
authors: JD
authors: Busch
authors: Glen A
authors: GA
authors: Scoles
authors: Kristina A
authors: KA
authors: Palma-Cagle
authors: Massaro W
authors: MW
authors: Ueti
authors: Lowell S
authors: LS
authors: Kappmeyer
authors: David M
authors: DM
authors: Wagner
mesh_terms: D000818:Animals; D001483:Base Sequence; D060085:Coinfection / Q000662:veterinary; D016172:DNA Fingerprinting / Q000379:methods / Q000662:veterinary; D016054:DNA, Protozoan / Q000737:chemistry / Q000235:genetics; D005819:Genetic Markers / Q000235:genetics; D014644:Genetic Variation; D005828:Genetics, Population; D005838:Genotype; D005845:Georgia / Q000453:epidemiology; D006239:Haplotypes; D006734:Horse Diseases / Q000453:epidemiology / Q000469:parasitology*; D006736:Horses; D018895:Microsatellite Repeats / Q000235:genetics*; D008969:Molecular Sequence Data; D010802:Phylogeny; D016053:RNA, Protozoan / Q000235:genetics; D012337:RNA, Ribosomal, 18S / Q000235:genetics; D017422:Sequence Analysis, DNA / Q000662:veterinary; D013781:Texas / Q000453:epidemiology; D016794:Theileria / Q000145:classification / Q000235:genetics / Q000302:isolation & purification*; D013801:Theileriasis / Q000453:epidemiology / Q000469:parasitology*
chemical_list: D016054:DNA, Protozoan; D005819:Genetic Markers; D016053:RNA, Protozoan; D012337:RNA, Ribosomal, 18S
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