Ovine theileriosis in China: a new look at an old story.

A fatal disease of sheep and goats in the northwestern part of China has in the past been reported to be due to Theileria lestoquardi. 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 18 small subunit ribosomal RNA (18S rRNA) 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 18S rRNA sequence of the Chinese parasite falls inside the clade consisting of Theileria species evidencing that it belongs to this genus. The 18S rRNA sequence of the Chinese parasite was found to be most closely related to Theileria buffeli and clearly divergent to T. lestoquardi, suggesting that it was a yet unrecognized Theileria species. The phylogenetic relationship of Theileria species infecting sheep and goats on the basis of their 18S rRNA gene structure was addressed. We report on the existence of at least two additional ovine and caprine piroplasm species, designated T. luwenshuni and T. uilenbergi.