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Review
. 2020 Nov 8;9(11):926.
doi: 10.3390/pathogens9110926.

Twenty Years of Equine Piroplasmosis Research: Global Distribution, Molecular Diagnosis, and Phylogeny

Sharon Tirosh-Levy  1 , Yuval Gottlieb  1 , Lindsay M Fry  2   3 , Donald P Knowles  2 , Amir Steinman  1
Affiliations
Review

Twenty Years of Equine Piroplasmosis Research: Global Distribution, Molecular Diagnosis, and Phylogeny

Sharon Tirosh-Levy et al. Pathogens. .

Abstract

Equine piroplasmosis (EP), caused by the hemoparasites Theileria equi, Theileria haneyi, and Babesia caballi, is an important tick-borne disease of equines that is prevalent in most parts of the world. Infection may affect animal welfare and has economic impacts related to limitations in horse transport between endemic and non-endemic regions, reduced performance of sport horses and treatment costs. Here, we analyzed the epidemiological, serological, and molecular diagnostic data published in the last 20 years, and all DNA sequences submitted to GenBank database, to describe the current global prevalence of these parasites. We demonstrate that EP is endemic in most parts of the world, and that it is spreading into more temperate climates. We emphasize the importance of using DNA sequencing and genotyping to monitor the spread of parasites, and point to the necessity of further studies to improve genotypic characterization of newly recognized parasite species and strains, and their linkage to virulence.

Keywords: Babesia caballi; Theileria equi; equine; equine piroplasmosis; genotyping.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
The life cycle of Theileria equi (TE) and Babesia caballi (BC) in the tick vector and in the equine host. RBC—equine red blood cells, WBC—equine while blood cells, SG—tick salivary glands.
Figure 2
Figure 2
Global prevalence of T. equi, and the distribution of T. equi 18S rRNA genotypes. The map was constructed based on epidemiological data published in the last 20 years (2000–2019). Endemic: over 30%, prevalent: 10–29%, sporadic: under 10% or singular outbreaks. Genotyping was performed on all sequences submitted to GenBank and classification was based on previously reported clades.
Figure 3
Figure 3
Global prevalence of B. caballi. The map was constructed based on epidemiological data published in the last 20 years (2000–2019). Endemic: over 30%, prevalent: 10–29%, sporadic: under 10% or singular outbreaks.
Figure 4
Figure 4
A representative phylogenetic tree of T. equi 18S rRNA genotypes. The tree included 18 sequences and 1373 positions. The tree was constructed using maximum likelihood, Tamura-Nei+G+I model with 1000 bootstrap repeats in MEGA7.
Figure 5
Figure 5
Representative phylogenetic trees of T. equi ema-1 (a) and ema-2 (b) genotypes. (a) The tree included 20 sequences and 540 positions. (b) The tree included 18 sequences and 800 positions. Both trees were constructed using maximum likelihood, Kimura 2-parameter model with invariable sites (+I) and 1000 bootstrap replicates in MEGA7.
Figure 6
Figure 6
Representative phylogenetic trees of B. caballi 18S rRNA (a) and rap-1 (b) genotypes. (a) The tree included 20 sequences and 1364 positions. The tree was constructed using maximum likelihood, Tamura-Nei model with gamma distribution (+G). (b) The tree included 18 sequences and 793 positions. The tree was constructed using maximum likelihood, Kimura 2-parameter model with evolutionarily invariable sites (+I). Both trees were created using 1000 bootstrap replicates in MEGA7.
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