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Parasites & vectors2020; 13(1); 267; doi: 10.1186/s13071-020-04133-y

Parasite load and genotype are associated with clinical outcome of piroplasm-infected equines in Israel.

Abstract: Equine piroplasmosis is a highly endemic protozoan disease of horses worldwide, caused by Theileria equi and Babesia caballi. While most horses in endemic areas are subclinically infected, the mechanisms leading to clinical outcome are vastly unknown. Moreover, since clinical signs of disease are not specific, and the prevalence in endemic areas is high, it is difficult to determine if equine piroplasmosis is the cause of disease. To identify possible mechanisms leading to the clinical outcome in an endemic area, we compared parasite loads and genotypes in clinically and subclinically infected horses. Methods: Blood was collected from horses with clinical signs consistent with equine piroplasmosis, and from apparently healthy horses in Israel. Packed cell volume and total solids were measured. Quantitative and diagnostic polymerase chain reaction were used to identify, quantify and classify equine piroplasmosis infection. Phylogenetic analyses were used to determine the genotype of both parasites. Results: For both parasites, clinical cases were associated with low mean packed cell volume and high mean parasite load (P < 0.001), enabling the determination of a cut-off value to distinguish between clinically and subclinically infected horses. Samples of Theileria equi from subclinical horses were classified into three different 18S rRNA genotypes, D (n = 23), A (n = 12) and C (n = 5), while samples from all clinical cases (n = 6) were classified as genotype A. The sequences of T. equi equi merozoite antigens 1 (ema-1, n = 9) and 2 (ema-2, n = 11) genes were fairly conserved and did not differ between clinical and subclinical cases. Babesia caballi rhoptry associated protein-1 (rap-1) was classified into sub-genotypes A1 (n = 14) and A2 (n = 5) with no association to clinical outcome. Classification of the 18S rRNA gene (sub-genotypes B1 and B2) agreed with the rap-1 classification. Conclusions: The results of this study suggest that quantification of parasite loads of infected horses may be used to distinguish between infections resulting in disease and subclinical cases. Although number of clinical cases is limited, we identified T. equi 18S rRNA genotype A to be associated with clinical disease. This finding emphasizes the importance of in-depth genetic characterization of T. equi genotypes to identify possible markers for virulence.
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Publication Date: 2020-05-20 PubMed ID: 32434550PubMed Central: PMC7240905DOI: 10.1186/s13071-020-04133-yGoogle Scholar: Lookup
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Summary

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This research article investigates the clinical effects of equine piroplasmosis, a widespread parasite-borne disease affecting horses. The study explores the relationship between the level of infection and the specific genotype of the parasite, along with their influence on the health outcomes of infected horses in Israel.

Objective and Methodology

  • The primary objective of this study was to gain insights into mechanisms that lead to different outcomes in horses infected with equine piroplasmosis, a disease caused by Theileria equi and Babesia caballi parasites.
  • The researchers sought to differentiate between clinical and subclinical instances of infection, the latter being cases wherein the infection results in no evident clinical symptoms. This distinction can be challenging due to the non-specific nature of the disease’s symptoms and its high prevalence in endemic regions.
  • To achieve this, blood samples were taken from horses showing symptoms of equine piroplasmosis as well as from seemingly healthy horses for comparison. Various parameters such as packed cell volume and total solids were measured, and molecular techniques such as PCR (Polymerase chain reaction) were utilized to identify, quantify, and classify the infection.
  • Genotyping of the parasites was accomplished through phylogenetic analyses, which also allowed determination of the genotypes associated with clinically and subclinically infected horses.

Results

  • Results indicated that clinical cases were associated with a lower mean packed cell volume and a higher mean parasite load, enabling a cut-off value to distinguish between clinical and subclinical instances.
  • It was found that different genotypes of Theileria equi were associated with the disease’s clinical and subclinical form. Three genotypes were found in subclinical horses (genotypes D, A, and C), while all clinical cases were associated with genotype A.
  • However, the sequences of two T. equi merozoite antigens, ema-1 and ema-2, were similar between clinical and subclinical cases. Babesia caballi samples also revealed no clear association between specific genotypes and the clinical outcome.

Conclusions

  • The study concludes that gauging the parasite load in infected horses could help differentiate between subclinical and clinical outcomes.
  • Despite the limited number of clinical cases, the study identifies T. equi 18S rRNA genotype A as the one associated with clinical disease. This identifies the role of specific T. equi genotypes in disease manifestation, and potentially opens doors to further study for early disease detection, prevention, and treatment based on genotype.

Cite This Article

APA
Tirosh-Levy S, Steinman A, Levy H, Katz Y, Shtilman M, Gottlieb Y. (2020). Parasite load and genotype are associated with clinical outcome of piroplasm-infected equines in Israel. Parasit Vectors, 13(1), 267. https://doi.org/10.1186/s13071-020-04133-y

Publication

Parasites & vectors
ISSN: 1756-3305
NlmUniqueID: 101462774
Country: England
Language: English
Volume: 13
Issue: 1
Pages: 267
PII: 267

Researcher Affiliations

Tirosh-Levy, Sharon
  • Koret School of Veterinary Medicine, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.
Steinman, Amir
  • Koret School of Veterinary Medicine, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.
Levy, Hadas
  • Koret School of Veterinary Medicine, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.
Katz, Yotam
  • Koret School of Veterinary Medicine, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.
Shtilman, Margarita
  • Koret School of Veterinary Medicine, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.
Gottlieb, Yuval
  • Koret School of Veterinary Medicine, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel. gottlieb.yuval@mail.huji.ac.il.

MeSH Terms

  • Animals
  • Babesia / genetics
  • Babesiosis / epidemiology
  • Babesiosis / parasitology
  • DNA, Protozoan / blood
  • Female
  • Genotype
  • Horse Diseases / parasitology
  • Horses / parasitology
  • Israel / epidemiology
  • Male
  • Parasite Load
  • RNA, Ribosomal, 18S / genetics
  • Theileria / genetics
  • Theileriasis / epidemiology
  • Theileriasis / parasitology

Conflict of Interest Statement

The authors declare that they have no competing interests.

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Citations

This article has been cited 5 times.
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