Molecular detection and genetic diversity of Anaplasma marginale based on the major surface protein genes in Thailand.

Anaplasma marginale is the rickettsial agent of anaplasmosis, a tick-borne disease, which affects cattle and other ruminants in tropical and subtropical areas of the world, and causing huge economic losses because of decreasing meat and milk production. In the present study, molecular methods have been used to determine the occurrence and genetic diversity of A. marginale, based on the genes encoding the major surface proteins (msps) genes, in blood samples from 520 cattle and 121 buffaloes in the north and northeastern regions of Thailand. The polymerase chain reaction (PCR) results based on the msp4 gene indicated that 66 (10.30%) cattle were positive for A. marginale, whereas no positive result was obtained from buffaloes. The phylogenetic analysis based on the maximum likelihood method using 13, 29 and 27 nucleotide sequences from msp2, msp4, msp5 clones, respectively, revealed that the sequences detected in this study are obviously distributed in different clusters. The sequence analysis demonstrated that msp2 gene is genetically diverse, while msp4 and msp5 genes are conserved in Thailand. These findings corroborated the diversity analysis of the same sequences, which showed 13, 27 and 27 haplotypes of the msp2, msp4 and msp5 genes, respectively. In addition, the entropy analyses of amino acid sequences exhibited 127, 75 and 51 high entropy peaks with values ranging from 0.27119 to 2.45831, from 0.14999 to 2.17552 and from 0.15841 to 1.05453 for MSP2, MSP4 and MSP5, respectively. Therefore, the results indicate a low molecular occurrence of A. marginale in cattle blood samples in Thailand. From these results; however, a high degree of genetic diversity was observed in the analyzed A. marginale population. Hence, our finding could be used to improve the immunodiagnostics and vaccination programs for anaplasmosis.