| anaplasma marginale msp1alpha genotypes evolved under positive selection pressure but are not markers for geographic isolates. | anaplasma marginale (order rickettsiales, family anaplasmataceae), a tick-borne pathogen of cattle, is endemic in tropical and subtropical regions of the world. many geographic isolates of a. marginale occur in the united states and have been identified by major surface protein 1a (msp1a), which varies in sequence and molecular weight due to different numbers of tandem 28- to 29-amino-acid repeats. the present study was undertaken to examine the genetic variations among isolates of a. marginale ... | 2003 | 12682152 |