Genetic diversity of Anaplasma marginale in Argentina

Bovine anaplasmosis caused by Anaplasma marginale is a worldwide major constraint to cattle production. The A. marginale major surface protein 1 alpha (msp1 alpha) gene contains a variable number of tandem repeats in the amino terminal region and has been used for the characterization of pathogen genetic diversity. This study reports the first characterization of A. marginale genetic diversity in Argentina based on msp1 alpha genotypes and its putative relationship with Rhipicephalus (Boophilus) microplus infestations. Herein, we analyzed whole blood bovine samples from anaplasmosis outbreaks in R. microplus infested (9 samples) and eradicated/free (14 samples) regions. Sequence analysis revealed the existence of 15 different msp1 alpha genotypes with 31 different repeat units. Six new repeat sequences were discovered in this study and 13/31 (42%) repeats were unique to Argentinean strains. The analysis of msp1 alpha repeat sequences according to R. microplus infestations resulted in three repeat groups: (i) found in tick-infested regions (20 repeats), (ii) found in tick free regions (6 repeats) and (iii) randomly distributed (5 repeats). Moreover, A. marginale msp1 alpha genetic diversity was higher in tick-infested regions than in tick free areas. These results, together with previous evidence suggesting that A. marginale msp1 alpha repeat units co-evolved with the tick vector, might represent an evidence of the role of tick-mediated transmission for the generation of pathogen genetic diversity. (C) 2009 Elsevier B.V. All rights reserved.