Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)

First Advisor

Stephen David Gaunt


Dogs were inoculated with Ehrlichia platys and either examined morphologically or infested with Rhipicephalus sanguineus (Acari: Ixodidae) ticks for studies of disease pathogenesis and vector transmission. Dogs inoculated with Ehrlichia platys were sequentially necropsied at 1 week intervals from 7 to 35 days post inoculation. Ehrlichia platys-infected dogs had generalized lymphadenomegaly and histopathologic evidence of lymphoid hyperplasia and proliferation of resident tissue macrophages in lymph nodes, liver, and spleen. Most dogs had mild hemorrhage or edema in multiple organs, including splenic intrafollicular hemorrhages in all dogs except one. Livers had hepatocellular vacuolation in addition to portal lymphangiectasia and Kupffer cell hyperplasia. All dogs developed thrombocytopenia and had increased numbers of megakaryocytes in bone marrow and spleen. Ultrastructurally, dogs had electron dense deposits associated with pulmonary interalveolar spetal basement membranes, and intravascular coagulation and intracellular ehrlichial organisms were observed rarely. Increased activity of alanine aminotransferase and alkaline phosphatase occurred in dogs at 7 day post inoculation. The lesions caused by Ehrlichia platys were similar to those observed in dogs acutely infected with Ehrlichia canis. Laboratory maintained Rhipicephalus sanguineus nymph ticks were infested on Ehrlichia platys-infected dogs during initial parasitemia and thrombocytopenia. Molted Ehrlichia platys exposed adult ticks were studied by infesting susceptible dogs to assess vector capability, and by examination of tick midgut and salivary gland by light and transmission electron microscopy and immunocytochemistry. Ehrlichia platys organisms were not detected in exposed ticks, and ticks did not pass Ehrlichia platys to susceptible dogs. Rhipicephalus sanguineus may not transmit Ehrlichia platys infection. Avidin-biotin-immunoperoxidase immunocytochemical stains were developed for detecting antigens of Ehrlichia platys and Ehrlichia risticii. Formalin fixation was shown to inactivate ehrlichial antigens in infected cells and tissues. Acetone fixation allowed detection of ehrlichial antigens with the immunocytochemical techniques in infected cell smears and in paraffin-embedded tissue sections. Ehrlichia platys antigens were not detected in tissues from infected dogs by immunocytochemical staining.