Ehrlichia canis is an obligate, intracellular bacterium that acts as the causative agent of Ehrlichiosis, a disease most commonly affecting canine species. This pathogen is present throughout the United States (but is most prominent in the South),[2] South America, Asia, and Africa.[3] First defined in 1935, E. canis emerged in the United States in 1963 and its presence has since been found in all 48 contiguous United States.[2][4] Reported primarily in dogs, E. canis has also been documented in felines and humans where it is transferred most commonly via Rhipicephalus sanguineus, the brown dog tick.