Ehrlichiosis, a potentially life-threatening disease, is becoming more frequently diagnosed, especially in the southern United States. Symptomatically, the clinical picture closely resembles Rocky Mountain Spotted Fever, with the development of headache and fever following a tick bite. The putative causative agent is a tickborne rickettsial-like organism that shares many antigenic determinants with Ehrlichia canis, a known canine pathogen. This tickborne organism may in fact be E canis.
This bacterium is an obligate intracellular organism that preferentially infects lymphocytes, monocytes, and neutrophils. Ehrlichiosis probably accounts for a significant portion of what was previously diagnosed “seronegative Rocky Mountain Spotted Fever” cases.’
Our understanding of this new disease has increased dramatically since the first case of human illness attributable to E canis was diagnosed in 1986. Treatment is curative, and therapy, typically with tetracyclines, must be instituted early to avoid disease progression and even death.