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Ehrlichia spp. are obligate intracellular bacteria with tropism for hematopoietic cells. Monocytic ehrlichioses in dogs and humans are transmitted by ticks and primarily caused by E. canis and E. chaffeensis, respectively. E. canis causes canine monocytic ehrlichioses (CME), a potentially fatal
disease in dogs that requires rapid and accurate diagnosis in order to initiate appropriate therapy leading to a favorable prognosis. CME is characterized by three stages; 1) acute, 2) subclinical and 3) chronic. Dogs infected with E. canis remain infected for their entire lives, even after receiving antibiotic treatment with doxycycline. The prevalence of E. canis is dependent on the distribution of the vector, Rhipicephalus sanguineus tick, which occurs mainly in tropical and subtropical regions. The agent causing canine granulocytic ehrlichiosis (CGE) in Europe has been determined by nucleotide sequencing of the 16S rRNA gene to be similar to both Ehrlichia equi and E. phagocytophila (Anaplasma phagocytophila), and is identical to the agent of human granulocytic ehrlichiosis (HGE). The vector of this pathogen in Europe is the common European tick, Ixodes ricinus and its reservoir – wild and domestic animals. Two distinct clinical
disease syndromes, including chronic, moderate to sever anemia and polyarthritis, are associated with CGE. In areas infested with vectors of tick-borne agents known to be endemic for
Lyme disease, veterinarians may suspect ehrlichiosis in dogs.