Canine Ehrlichiosis (tropical canine pancytopenia): A review

Tropical canine pancytopenia (TCP), a disease of dogs caused by the rickettsial agent, Ehrlichia canis, is being recognized with increased frequency in many parts of the world. The brown dog tick, Rhipicephalus sanguineus, is an efficient vector of E. canis and transstadial transmission occurs. Infections persist and are characterized by rising antibody titers and hypergammaglobulinemia. Dogs cleared of infection with tetracycline are fully susceptible to reinfection with the homologous strain of E. canis and often develop severe disease. Experimental infections in beagle and German shepherd dogs have shown that severity of disease is related to the breed of dog. German shepherd dogs often develop a severe hemorrhagic syndrome 60 or more days following infection. Recent studies have shown that bone marrow hypoplasia is important in the pathogenesis of severe chronic TCP. Differences in response to infection may reflect underlying immunological defects, particularly in the cell-mediated system.