Molecular detection and characterization of p44/msp2 multigene family of Anaplasma phagocytophilum from Haemaphysalis longicornis in Mie Prefecture, Japan.

Anaplasma phagocytophilum is an obligate intracellular bacterium and causes human granulocytic anaplasmosis (HGA), a tick-borne emerging infectious disease. This bacterium expresses a variety of 44-kDa major outer membrane proteins encoded by a p44/msp2 multigene family to avoid host immune defense. We previously detected A. phagocytophilum p44/msp2 from one tick of Haemaphysalis longicornis in Mie Prefecture, Japan in 2008. In this study, we further investigated total 483 H. longicornis ticks (220 adults and 263 nymphs) collected in Mie Prefecture by p44/msp2 targeting PCR assay for the characterization of p44/msp2 multigene family of A. phagocytophilum in Japan. Six of 483 ticks tested were PCR-positive for A. phagocytophilum p44/msp2 and these positive individuals were all nymphs at tick life stage. Cloning, sequence, and phylogenetic analyses of the amplicons revealed that 11 p44/msp2 clones obtained shared the similarities of 54.9-99.3 % with 27 previously-identified clones from HGA patients in Japan based on amino acid sequences, especially 6 p44/msp2 clones had the high similarities of 97.2-99.3% with the 3 previously-identified clones (FJ417343, FJ417345, FJ417357). Thus, this study provides the information for public health significance regarding A. phagocytophilum infection transmitted by H. longicornis ticks, especially at the nymphal stage, in Japan.