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The emergence of drug resistance and adverse side effects of current bovine babesiosis treatment suggest that the search of new drug targets and development of safer and effective compounds are required. This study focuses on dihydroorotate dehydrogenase (DHODH), the fourth enzyme of pyrimidine biosynthesis pathway as a potential drug target for bovine babesiosis. Recombinant Babesia bovis DHODH protein (rBboDHODH) was produced in Escherichia coli and used for characterization and measurement of enzymatic activity. Furthermore, the effects of DHODH inhibitors were evaluated in vitro. The recombinant B. bovis DHODH histidine fusion protein (rBboDHODH) had 42.4-kDa molecular weight and exhibited a specific activity of 475.7 ± 245 Unit/mg, a Km = 276.2 µM for L-dihydroorotate and a Km= 94.41 µM for decylubiquinone. A 44-kDa band of native BboDHODH was detected by Western blot analysis and found in parasites mitochondria using a confocal microscope. Among DHODH inhibitors, atovaquone (ATV) and leflunomide (LFN) significantly inhibited the activity of rBboDHODH as well as the growth of B. bovis in vitro. The half maximal inhibitory concentration (IC50) of ATV and LFN was 2.38 ± 0.53 nM and 52.41 ± 11.47 µM, respectively. These results suggest that BboDHODH might be a novel target for development of new drug for treatment of B. bovis infection.

Ovine theileriosis is a tick-borne disease that restricts the development of small ruminant husbandry in northern China. In this study, we report on a molecular epidemiological survey of ovine Theileria spp. in 198 blood samples taken from sheep in northern China. The DNA samples were screened by a nested polymerase chain reaction (PCR) targeting the 18S rRNA gene of ovine Theileria spp. The prevalence of ovine Theileria spp. in Yanji, Nongan, Longjing, Toudao and Jinchang was 80%, 40%, 37%, 24% and 32%, respectively. The sequencing analyses approved the present of the T. orientalis and/or T. luwenshuni in these regions. Taken together, we have demonstrated a high incidence of Theileria spp. in northern China that calls for the need to design effective control programs for ovine theileriosis.