# Molecular Prevalence and Genotypic Diversity of Theileria equi in Xinjiang, China, Based on Three Genes

## TL;DR

This study examines the spread and genetic diversity of Theileria equi, a tick-borne parasite affecting horses in Xinjiang, China, using three genes to identify regional differences and dominant genotypes.

## Contribution

The first comprehensive genotyping of Theileria equi in Xinjiang using three molecular markers and haplotype network analysis.

## Key findings

- The overall infection rate of Theileria equi in Xinjiang was 38.41%, with Tacheng having the highest prevalence at 86.27%.
- Genotype E of the 18S rRNA gene and genotype A of the EMA-1 gene were the most prevalent in the region.
- Urumqi showed the highest genetic diversity of Theileria equi, suggesting it may be a hotspot for parasite evolution.

## Abstract

Equine theileriosis, a disease caused by the protozoan parasite Theileria equi and trans-mitted by ticks, represents a significant threat to equine health and the equine industry in Xinjiang, China. To investigate the current prevalence and genetic characteristics of the parasite, we conducted a molecular survey and genetic analysis. Blood samples were collected from 440 apparently healthy horses across four regions (Altay, Ili, Tacheng, and Urumqi). The overall infection rate was 38.41%, with prevalence varying significantly by region; it was highest in Tacheng (86.27%) and lowest in Altay (20.88%). Genetic characterization based on three target genes revealed the following: analysis of the 18S rRNA gene identified two distinct genotypes (E and A), with genotype E being overwhelmingly dominant. All parasites tested belonged to genotype A for the EMA-1 gene. For the mitochondrial COI gene, local strains showed a close phylogenetic relationship to isolates reported from France and Senegal. Haplotype network analysis indicated that Urumqi harbored the highest genetic diversity, suggesting it may be a hotspot for parasite evolution. This study provides the first integrated genetic dataset for T. equi in Xinjiang using three different molecular markers, offering crucial insights for monitoring and targeted control of this important disease.

Equine theileriosis, caused by the protozoan parasite Theileria equi, represents a significant economic threat to the equine industry. In Xinjiang, China, an endemic area for this disease, systematic research on the genetic diversity of T. equi has been notably lacking. The aim of this study was to obtain molecular epidemiological data pertaining to the parasite in selected regions of Xinjiang, China, and analyze the genetic characteristics (including 18S rRNA, EMA-1, and COI genes) and genotype distribution patterns of isolates from these regions, providing a scientific basis for developing targeted prevention and control strategies. Blood samples were collected from 440 horses across four regions (Altay, Ili, Tacheng, and Urumqi) and subjected to PCR assays. Positive samples were sequenced for phylogenetic and haplotype network analyses, and genetic diversity indices were calculated. The overall infection rate of T. equi was 38.41% (169/440), with Tacheng having the highest prevalence (86.27%) and Altay the lowest (20.88%); these regional differences were statistically significant. Phylogenetic analysis identified two genotypes of the 18S rRNA gene: genotype E (predominant) and genotype A. All EMA-1 sequences clustered exclusively within genotype A. Notably, all COI gene sequences formed a monophyletic group, exhibiting closer genetic relationships to isolates from France and Senegal. This study presents the first comprehensive genotyping of T. equi in Xinjiang based on three target genes and constructs an associated haplotype network. The analysis identified 18S rRNA genotype E and EMA-1 genotype A as the predominant genotypes. Furthermore, the genetic diversity of T. equi was found to be higher in Urumqi than in the other regions studied.