Ribosomal small-subunit RNA gene-sequence analysis of Theileria lestoquardi and a Theileria species highly pathogenic for small ruminants in China.

A fatal disease of sheep and goats in the northwestern part of China has been reported to be due to Theileria lestoquardi (syn. T. hirci). However, some characteristics of the causative agent are not in accordance with attributes ascribed to this parasite. We therefore determined the nucleotide sequence of the small-subunit ribosomal RNA (srRNA) gene of T. lestoquardi and the parasite identified in China and compared it with that of other Theileria and Babesia species. In the inferred phylogenetic tree the srRNA sequence of the Chinese parasite was found to be most closely related to T. buffeli and clearly divergent from T. lestoquardi, suggesting that it is an as yet unrecognized Theileria species. Extensive structural similarities were observed between the srRNA sequences of T. lestoquardi and T. annulata, revealing a close phylogenetic relationship between these two Theileria species. On the basis of the srRNA nucleotide sequence, polymerase chain reaction (PCR) primers were designed that specifically amplified genomic DNA of the Chinese Theileria species. These primers may be valuable tools in future epidemiology studies.