RESUMEN
The objective of this study was to identify Anaplasma marginale strains in dairy heifers from farms with a history of anaplasmosis in the northwest region of the State of Minas Gerais, Brazil. Among the examined animals of the four farms, the overall prevalence total of A. marginale was 55.7 % for gene msp5 and 36.7 % for blood smear. Thirty DNA samples (from 24 asymptomatic and six symptomatic animals) positive for A. marginale msp1α were sequenced to study genotype and strain diversity. The majority (28/30) were the E genotype, followed by C (1/30) and G (1/30). Thirteen different strains were found: α-ß-F-F-F (nine animals), 13-27-27 (three animals), τ-27-18 (three animals), α-ß-ß- BRA1-31 (three animals), α- 22-1318 (three animals), 80-F-F- F-F (three animals), and α -22-13-13, α-ß-ß-Ð, M-φ-φ-φ-φ-F, 42-25- 25-31, Q-Q-Q-M, B-Q-B-Q-B-M, and 16-17-F-F (one animal each). A new structure repeated in tandem was described and named BRA 1 (TDSSSASGVLSQSGQASTSSQLG). The α-ß-F-F-F strain was present in all animals with acute anaplasmosis and in three animals asymptomatic. Thus, although 13 strains were observed in the animals evaluated, only the α-ß-F-F-F strain was identified during occurrence of acute disease and mortality, we suggest that this strain has important pathogenicity for calves in northeastern Minas Gerais.