Genetic characterization of Theileria equi infecting horses in North America

Evidence for a limited source of U.S. introductions

Carina M. Hall, Joseph D. Busch, Glen A. Scoles, Kristina A. Palma-Cagle, Massaro W. Ueti, Lowell S. Kappmeyer, David M Wagner

Research output: Contribution to journalArticle

26 Citations (Scopus)

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 F ST 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.

Original languageEnglish (US)
Article number35
JournalParasites and Vectors
Volume6
Issue number1
DOIs
StatePublished - 2013

Fingerprint

Theileria
North America
Microsatellite Repeats
Horses
Ticks
Single Nucleotide Polymorphism
Disease Outbreaks
Parasites
Babesiosis
DNA Fingerprinting
Mexico
rRNA Genes
Haplotypes
Nucleotides
Clone Cells
Alleles
Genotype
Genome
Infection
Population

Keywords

  • 18S rRNA gene
  • Babesia equi
  • Equine piroplasmosis
  • Microsatellite
  • Population genetics
  • Theileria equi

ASJC Scopus subject areas

  • Parasitology
  • Infectious Diseases
  • Medicine(all)

Cite this

Genetic characterization of Theileria equi infecting horses in North America : Evidence for a limited source of U.S. introductions. / Hall, Carina M.; Busch, Joseph D.; Scoles, Glen A.; Palma-Cagle, Kristina A.; Ueti, Massaro W.; Kappmeyer, Lowell S.; Wagner, David M.

In: Parasites and Vectors, Vol. 6, No. 1, 35, 2013.

Research output: Contribution to journalArticle

Hall, Carina M. ; Busch, Joseph D. ; Scoles, Glen A. ; Palma-Cagle, Kristina A. ; Ueti, Massaro W. ; Kappmeyer, Lowell S. ; Wagner, David M. / Genetic characterization of Theileria equi infecting horses in North America : Evidence for a limited source of U.S. introductions. In: Parasites and Vectors. 2013 ; Vol. 6, No. 1.
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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 F ST 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.",
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T2 - Evidence for a limited source of U.S. introductions

AU - Hall, Carina M.

AU - Busch, Joseph D.

AU - Scoles, Glen A.

AU - Palma-Cagle, Kristina A.

AU - Ueti, Massaro W.

AU - Kappmeyer, Lowell S.

AU - Wagner, David M

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N2 - 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 F ST 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.

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