Characterization of Anaplasma ovis strains using the major surface protein 1a repeat sequences

Background: Anaplasma ovis is one of the tick-transmitted pathogens of small ruminants. It causes ovine anaplasmosis and widely distributed in the world. In contrast to extensive worldwide genetic diversity of A. marginale and A. phagocytophilum, there are few reports on the classification of A. ovis strains. This study was conducted to investigate the occurrence and characterize A. ovis strains from goats and sheep from 12 provinces in China. Methods: The occurrence of A. ovis DNA was tested in 552 goats and sheep, by PCR based on the msp4 gene. Positive samples were used for the amplification of the msp1a gene of A. ovis. The Msp1a amino acid repeats were further identified and used for the characterization of A. ovis strains. Results: The results showed that 79 (14.3%) goats and sheep were positive for A. ovis. The infection rates of A. ovis among different study sites ranged from 0 to 100%, and were significantly higher in sheep (26. 6%, 45/169) than in goats (8.9%, 34/383) (chi(2) = 21.403, df = 1, P < 0.001). The msp4 gene sequences of these isolates were 99.8-100% identical to each other, and they represented two sequence types. Forty-four partial msp1a gene sequences containing the repeat sequences were obtained from A. ovis-positive samples. After translation to amino acid sequences, 24 Msp1a repeats with 33 to 47 amino acids, which corresponded to 19 genotypes of A. ovis, were recognized in goats and sheep in China. Conclusions: Anaplasma ovis is widely distributed in the investigated geographical regions. The msp4 gene of A. ovis had high sequence identity and was unable to be used to discriminate different strains. The Msp1a could be used as a genetic marker for characterizing A. ovis, and 19 genotypes of A. ovis were recognized in domestic small ruminants in China. The present study revealed, for the first time, the genetic diversity of A. ovis based on the analyses of Msp1a amino acid repeats.