Authors: Nehra Anil Kumar, Kumari Ansu, Moudgil Aman Dev, Vohra Sukhdeep
Journal: Frontiers in veterinary science
Summary
# Equine Theileriosis: Clarifying the Genetic Diversity of *Theileria equi* Equine theileriosis, a tick-borne parasitic disease of significant economic importance to the equine industry globally, presents a complex epidemiology complicated by inconsistent genotyping nomenclature that has hindered comparative research. Kumar and colleagues conducted a comprehensive phylogenetic analysis of 736 complete *Theileria equi* sequences from GenBank, focusing on the V4 hypervariable region of the 18S rRNA gene, and constructed a maximum likelihood tree using the Kimura 2-parameter model to establish a standardised classification system. The analysis definitively identified four distinct genotypes (A–D), with clade B being predominant at 52.85% of sequences, followed by A (27.58%), C and D (both 9.78%), and resolved previous taxonomic confusion by demonstrating that earlier studies' genotypes B and E were synonymous. Genotypes A and C showed the widest geographical distribution across five continents (particularly Asia and Africa), whilst genotypes B and D were confined to three continents with more restricted prevalence; notably, genotypes A and C uniquely occurred in the Americas, suggesting distinct epidemiological patterns. For equine practitioners, this standardised four-genotype framework provides a more reliable foundation for understanding disease prevalence in different regions, potentially informing targeted control strategies and vaccination development, whilst the identification of molecular signatures between genotypes may aid in developing more accurate diagnostic tools and monitoring parasite evolution.
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Practical Takeaways
- •Standardized nomenclature (genotypes A-D) is now established for T. equi, improving consistency in diagnostic reporting and research communication across laboratories and regions.
- •Understanding geographical distribution of genotypes can inform risk assessment and quarantine protocols for imported horses, particularly for genotypes A and C which span multiple continents.
- •Genetic diversity variations among genotypes may have implications for vaccine development and diagnostic test sensitivity, warranting investigation of whether different genotypes respond differently to treatment or prevention strategies.
Key Findings
- •Phylogenetic analysis of 736 T. equi sequences identified four distinct genotypes (A, B, C, D) with high bootstrap support, consolidating previous inconsistent nomenclature systems.
- •Genotype B was the most dominant (52.85%), followed by genotype A (27.58%), with genotypes C and D each representing 9.78% of sequences.
- •Genotype C showed the highest genetic diversity (91.0-100% identity), while genotypes B and D showed the lowest (95.7-100% identity).
- •Genotypes A and C had wide geographical distribution across 31 and 13 countries respectively, while genotypes B and D showed limited distribution restricted to Asian, African, and European continents.