More than 185 species, strains and unclassified Theileria parasites are categorized in the Entrez Taxonomy.
The accurate diagnosis and proper identification of the causative agents are important for understanding the
epidemiology, prevention and appropriate treatment. This study aims to discuss the importance of two
genes of Theileria annulata 18S ribosomal RNA (18S rRNA) and Theileria annulata merozoite surface
antigen (Tams1) for phylogenetic analysis of molecular data. Eight Theileria annulata isolates including
S15 Iran vaccine strain, six T. annulata field isolates and one Iraq T. annulata field isolate were studied in
this study. The 18S rRNA and Tams1 gene sequences were investigated by phylogenetic analysis after
DNA extraction, PCR, and DNA sequencing. Sequence fragments of about 1410 to 1412 bp of the
complete 18S rRNA gene and 778 nucleotides of Tams1 gene sequences were used in the analysis of
nucleotide diversity. Sequence alignment and phylogenetic analysis were performed by constructing the
phylogenetic tree and identity matrix based on two above genes. The results of the study revealed, the 18S
rRNA is informative in estimation of relationships among Theileria species and strains, but the Tams1
seems to be appropriate for analysis of the molecular antigenicity in vaccine development.