Tropical Canine Pancytopenia: Clinical, Hematologic, and Serologic Response of Dogs to Ehrlichia canis Infection, Tetracycline Therapy, and Challenge Inoculation

Abstract

For further elucidation of the pathogenesis of tropical canine pancytopenia (TCP), 14 German shepherd dogs were evaluated following infection with Ehrlichia canis, therapy with tetracycline, and challenge inoculation. Nine dogs developed severe chronic TCP, characterized by severe pancytopenia, hemorrhage, and secondary bacterial infection. In all dogs antibody titers increased for more than 80 days after infection, and all dogs developed hypergammaglobulinemia. Prolonged and incomplete hematologic recovery followed termination of infection by tetracycline therapy in dogs with severe chronic disease. After treatment levels of serum γ-globulin returned to normal. A second inoculation of treated dogs with E. canis resulted in reinfection and hypergammaglobulinemia, but with variable increases in serum antibody. Results indicate that aplastic anemia may be important in the pathogenesis of severe chronic TCP, and that increasing antibody titers and hypergammaglobulinemia reflect persistent infection with E. canis. Differences in response to challenge may reflect underlying immunologic differences between dogs with severe disease and those that do not become seriously ill.