Abstract
Background:
Goat theileriosis is a disease caused by a protozoan parasite Theileria ovis transmitted by blood-feeding ticks. It is an emerging disease that is of concern because of its high incidence and impact on animal health and productivity. In contrast to goats, goats are often considered more tolerant of hemoparasitic infections. However, a growing body of evidence indicates that goats can also be significant reservoirs of T. ovis, where the parasite can persist and be transmitted to other hosts in endemic regions. However, in Iraq, research describing the molecular characteristics of T. ovis infections in goats is almost nonexistent.

Aim:
This study aimed to provide the first molecular characterization of T. ovis parasite infections in goats in the central region of Iraq and to characterize T. ovis local isolates using 18S ribosomal RNA (rRNA) gene partial sequencing and phylogenetic analysis.

Methods:
Genomic DNA was extracted from whole blood samples collected from goats using a commercial kit. The molecular detection of T. ovis was performed using a nested conventional PCR that amplifies the 18S rRNA gene. Positive PCR products were purified, and Sanger sequencing was performed. Sequences were edited and deposited in the GenBank database. The sequences were then analyzed and compared using the NCBI-BLAST database for species confirmation. Phylogenetic analysis was conducted using the maximum likelihood method based on the Tamura–Nei model. The nucleotide similarity between local and global T. ovis isolates was determined using multiple sequence alignment.

Results:
The DNA of T. ovis was successfully amplified by nested PCR in the blood samples of goats with the predicted 520 bp amplicon related to the 18S rRNA gene. Sequencing of 10 representative goat-derived blood samples was performed, and the results were deposited in the GenBank database with the following accession numbers: PX755072 to PX755081. All isolates were confirmed as T. ovis from the BLAST analysis, which showed a cross-nucleotide identity of 98.75%–98.81% from the global references of Brazilian, Egyptian, Turkish, Pakistani, Chinese, Japanese, and Iraqi T. ovis. Phylogenetic analysis showed that all goat isolates clustered together in the T. ovis clade, and the isolates had robust close evolutionary relationships with T. ovis strains from other countries. Little to no sequence divergence was observed in the goat isolates, as seen in the other consensus sequence of most of the constituents in the multiple sequence alignment.

Conclusion:
Theileria ovis infection in goats from Central Iraq and genetic constituents of T. ovis caprine isolates are closely related to other global T. ovis. This study emphasizes the need to consider goats as a significant circulating host of T. ovis and the need to integrate goats into molecular surveillance programs to identify tick-borne hemoparasites.

Key words: 18S rRNA gene; Goats; Nested PCR; Phylogenetic analysis; Theileria ovis.