ABSTRACT
INTRODUCTION Anaplasmataceae comprise a group of intracellular alpha proteobacteria that are pathogenic for certain mammals, including humans and cattle, for which the host cells are of bone marrow or hematopoietic origin including erythrocytes, monocytes or macrophages, neutrophils, and platelets. Members of this family share a high degree of nucleotide sequence similarity with respect to several chromosomal genes, such as rrs, groESL operon, citrate synthase gltA, ribosomal polymerase RpoB, and the ankyrin Ank gene (1). The organisms grow within a cytoplasmic vacuole containing one to many individual organisms; such structures resembled mulberries when observed by light microscopy, leading to the term “morulae.” The first discovered agent was named Anaplasma marginale by Theiler in 1910. Since that time, several other members of the family have been described from animals and humans. Recent improvements in molecular phylogenetic methods led to a modification of the taxonomy of the Anaplasmataceae in 2001 (2). This reorganization of the genera within the family was based on comparison of sequences obtained from rrs (16S rRNA encoding gene) and the groESL operon, which contains a spacer region between groES and the groEL heat shock protein genes and is thought to be more phylogenetically informative than the coding regions (3,4). Multiple alignment and analysis of the rrs gene sequences as well as that of the groESL operon gene identified four clades: Anaplasma, Ehrlichia, Neorickettsia, and Wolbachia. Although the nomenclature largely remained unchanged, some taxa, such as Cowdria ruminantium, were reclassified (2). Analysis of other gene sequences as well as the complete genome sequencing of several species of the family such as A. phagocytophilum, Ehrlichia chaffeensis, E. ruminantium, Neorickettsia sennetsu, and Wolbachia pipientis further confirm the new organization of the family Anaplasmataceae and will be discussed in detail in this review (5). The Anaplasmataceae now include four genera: the genus Anaplasma, the genus Ehrlichia, the genus Neorickettsia, and the genus Wolbachia.
