Characterization of p44/msp2 multigene family of Anaplasma phagocytophilum from two different tick species, Ixodes persulcatus and Ixodes ovatus, in Japan.

Anaplasma phagocytophilum, which belongs to the order Rickettsiales, is an obligate intracellular bacterium and causes an emerging, tickborne, and febrile infectious disease, anaplasmosis, in humans and other mammals. This bacterium expresses a variety of 44-kDa immunodominant proteins encoded by the p44/msp2 multigene family on the surface for the purpose of avoiding the host immune defense due to the antigenic variation. In Japan, little is known about the molecular and biological features of A. phagocytophilum. In this study, we tried to characterize in detail the p44/msp2 multigene family of A. phagocytophilum from two tick species, Ixodes persulcatus and I. ovatus in Japan. A total of 174 amino acid sequences from the recombinant p44/msp2 clones after TA cloning of the amplicons obtained from the ticks were phylogenetically analyzed. The results showed that most of the clone sequences from I. ovatus were very similar to each other, but the sequences from I. persulcatus were diverse, and the sequences from the ticks were distinct from those from a wild deer that was previously reported. These findings suggest that Ixodes ticks are probably responsible for the transmission of certain genetic variants of A. phagocytophilum and that additional organism selection might occur in I. ovatus.