Evolution and diversity of the EMA families of the divergent equid parasites, Theileria equi and T. haneyi.
Abstract: The equine parasite Theilera equi continues to curtail global equine commerce due primarily to its ability to persist indefinitely in the immunocompetent horse. Details regarding the parasite life cycle, pathogenesis and mechanism of persistence remain unclear. The recently discovered T. haneyi is also capable of persistence in the horse, creating a potential reservoir for additional infections. These two divergent parasites share a unique gene family that expresses surface merozoite antigens, or equi merozoite antigens (EMAs). The EMA family was maintained in number and size in both parasites despite a species divergence of over 30 million years ago. This family is unique amongst Theilerias in number, structure and biochemical properties. In silico analysis revealed no evidence of selection for diversity within this family, indicating a role in host adaptation and persistence rather than antigenic variation and immune escape. Biochemical analysis revealed the presence of a conserved domain, homologous to the hemolysin toxin found in cobra venom. This finding combined with data from protein interaction prediction models may indicate interaction with the structural components of the host erythrocyte and a role in merozoite entry or escape. Additional predicted protein interactions focus on disruption of the enzymatic functions of the host cell, potentially resulting in enhanced parasite survival.
Copyright © 2018 Elsevier B.V. All rights reserved.
Publication Date: 2018-12-18 PubMed ID: 30576837DOI: 10.1016/j.meegid.2018.12.020Google Scholar: Lookup
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- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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The study offers insights into the behavior and evolution of two horse parasites, Theilera equi and T. haneyi. It reveals the mechanics of their persistence in horses’ immune systems, their impact on global equine commerce and highlights a unique gene family – equi merozoite antigens (EMAs), which may play a significant role in both parasites’ survival mechanisms.
Parasite Background and Impact on Equine Commerce
- Theilera equi and T. haneyi are horse parasites that have been able to continuously survive within horses, even those with fully functioning immune systems.
- This ability to persist indefatigably in the host leads to ongoing infections and significantly hinders global equine commerce.
- The detailed understanding of the parasites’ life cycle, pathogenesis, and persistence mechanics remains an area of active investigation.
Unique Gene Family – EMA
- Both T. equi and T. haneyi share a unique gene family referred to as equi merozoite antigens (EMAs).
- The EMA family has maintained its number and size in both parasites, despite the species having diverged over 30 million years ago.
- The EMAs are exceptional among Theilera species in terms of their number, structure, and biochemical properties.
- A study conducted using in silico analysis showed no evidence of selection for diversity within the EMA family, suggesting an important role in host adaptation and persistence rather than variation to elude the immune system.
Conserved Domain and Potential Interactions
- In addition to the EMAs, a biochemical analysis identified a conserved domain in the parasites, similar to the hemolysin toxin found in cobra venom.
- This discovery along with protein interaction prediction models suggest that there could be interactions with the host’s structural components of red blood cells, potentially playing a part in parasite entry or escape.
- Also, the anticipated protein interactions aim at disrupting the enzymatic functions of the host cell, potentially paving the way for an improved survival rate of the parasite.
Cite This Article
APA
Wise LN, Kappmeyer LS, Knowles DP, White SN.
(2018).
Evolution and diversity of the EMA families of the divergent equid parasites, Theileria equi and T. haneyi.
Infect Genet Evol, 68, 153-160.
https://doi.org/10.1016/j.meegid.2018.12.020 Publication
Researcher Affiliations
- Department of Veterinary Microbiology and Pathology, College of Veterinary Medicine, Washington State University, Pullman, WA, USA; School of Veterinary Medicine, St. George's University, True Blue, Grenada. Electronic address: lwise1@sgu.edu.
- Animal Disease Research Unit, Agricultural Research Service, U.S. Department of Agriculture, Pullman, WA, USA.
- Department of Veterinary Microbiology and Pathology, College of Veterinary Medicine, Washington State University, Pullman, WA, USA.
- Animal Disease Research Unit, Agricultural Research Service, U.S. Department of Agriculture, Pullman, WA, USA; Department of Veterinary Microbiology and Pathology, College of Veterinary Medicine, Washington State University, Pullman, WA, USA; Center for Reproductive Biology, Washington State University, Pullman, WA, USA. Electronic address: Stephen.White@ars.usda.gov.
MeSH Terms
- Amino Acid Sequence
- Animals
- Antigens, Protozoan / chemistry
- Antigens, Protozoan / genetics
- Antigens, Protozoan / immunology
- Biodiversity
- Biological Evolution
- Codon
- Conserved Sequence
- Genome, Protozoan
- Horse Diseases / immunology
- Horse Diseases / parasitology
- Horses
- Host-Parasite Interactions / immunology
- Merozoites / immunology
- Theileria / genetics
- Theileria / immunology
- Theileriasis / immunology
- Theileriasis / parasitology
Citations
This article has been cited 6 times.- Coultous R, Gotić J, McCann M, Sutton D, Beck R, Shiels B. Novel equi merozoite antigen (ema-1) gene heterogeneity in a geographically isolated Theileria equi population in Croatia.. Parasit Vectors 2022 Oct 31;15(1):401.
- Bastos RG, Sears KP, Dinkel KD, Kappmeyer L, Ueti MW, Knowles DP, Fry LM. Development of an Indirect ELISA to Detect Equine Antibodies to Theileria haneyi.. Pathogens 2021 Feb 27;10(3).
- Tirosh-Levy S, Gottlieb Y, Fry LM, Knowles DP, Steinman A. Twenty Years of Equine Piroplasmosis Research: Global Distribution, Molecular Diagnosis, and Phylogeny.. Pathogens 2020 Nov 8;9(11).
- Tirosh-Levy S, Steinman A, Levy H, Katz Y, Shtilman M, Gottlieb Y. Parasite load and genotype are associated with clinical outcome of piroplasm-infected equines in Israel.. Parasit Vectors 2020 May 20;13(1):267.
- Bishop RP, Kappmeyer LS, Onzere CK, Odongo DO, Githaka N, Sears KP, Knowles DP, Fry LM. Equid infective Theileria cluster in distinct 18S rRNA gene clades comprising multiple taxa with unusually broad mammalian host ranges.. Parasit Vectors 2020 May 19;13(1):261.
- Sunday Idoko I, Tirosh-Levy S, Leszkowicz Mazuz M, Mohammed Adam B, Sikiti Garba B, Wesley Nafarnda D, Steinman A. Genetic Characterization of Piroplasms in Donkeys and Horses from Nigeria.. Animals (Basel) 2020 Feb 18;10(2).
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