Molecular phylogeny and biogeography of North American isolates of Anaplasma marginale (Rickettsiaceae : Ehrlichieae)

Anaplasma marginale (A. marginale) is a tick-borne ehrlichial pathogen of c attle that causes the disease anaplasmosis. Six major surface proteins (MSP s) have been identified on A. marginale from cattle and ticks of which thre e, MSP1a, MSP4 and MSP5, are from single genes and do not vary within isola tes. The other three, MSP1b, MSP2 and MSP3, are from multigene families and may vary antigenically in persistently infected cattle. Several geographic isolates have been identified in the United States which differ in morphol ogy, protein sequence and antigenic properties. An identifying characterist ic of A. marginale isolates is the molecular weight of MSP1a which varies i n size among isolates due to different numbers of tandemly repeated 28-29 a mino acid peptides. For these studies, genes coding for A. marginale MSP1a and MSP4, msp1 alpha and msp4, respectively, from nine North American isola tes were sequenced for phylogenetic analysis. The phylogenetic analysis str ongly supports the existence of a south-eastern clade of A. marginale compr ised of Virginia and Florida isolates. Analysis of 16S rDNA fragment sequen ces from the A. marginale tick vector, Dermacentor variabilis, from various areas of the United States was used to evaluate possible vector-parasite c o-evolution. Our phylogenetic analysis supports identity between the most p arsimonious tree from the A. marginale MSP gene data and the tree that refl ected the western and eastern clades of D. variabilis. These phylogenetic a nalyses provide information that may be important to consider when developi ng control strategies for anaplasmosis in the United States. (C) 2001 Elsev ier Science B.V. All rights reserved.