Immune response of ponies to experimental infection with Ehrlichia equi.

Four ponies experimentally infected with Ehrlichia equi developed substantial cell-mediated immune responses, as measured by the leukocyte migration-inhibition test. Serum anti-E equi antibodies up to 1:1,280 were demonstrated by the indirect fluorescent antibody test. Cell-mediated immune responses returned to a base-line value by day 200 after primary inoculation, but serum antibody titers persisted for at least 300 days after inoculation. Two additional susceptible ponies, which were inoculated with convalescent blood or organ homogenates from ponies recovered from acute equine ehrlichiosis, treated with tetracycline, and subsequently challenge exposed with E equi-infective blood, did not develop clinical disease. This study suggested that ponies are resistant to reinfection with E equi following clinical ehrlichiosis.

East Coast fever: cultivation in vitro of cell-free schizonts and merozoites of Theileria parva and their immunogenicity in cattle.

Cell-free schizonts and merozoites of Theileria parva and Theileria lawrencei, derived from parasitized lymphoid cell lines, were propagated in vitro using enriched medium. Use of radioisotopic markers showed that the bovine cell-independent parasites passed through a limited but marked replication by day 4. If normal bovine RBC were inoculated in vitro with the cell-free merozoites, development of piroplasms in the RBC occurred. Electron microscopic studies of the merozoites and piroplasms revealed their structure to be similar to previous descriptions. Cattle inoculated with T parva merozoites and schizonts and later challenge exposed with homologous stabilate developed leukopenia, showed low macroschizont index, and survived longer than unvaccinated controls.

Autologous lymphocyte-mediated cytotoxicity against monocytes in canine ehrlichiosis.

The 51Cr-release technique for detecting cytotoxicity had been adapted to immunologic studies of canine ehrlichiosis. Lymphocytes from dogs infected with Ehrlichia canis, cause of canine ehrlichiosis, were shown to be cytotoxic for autologous monocytes. The effect was dependent on the concentraton of lymphocytes, being optimal at 100:1 lymphocyte:monocyte ratio. Neither immune serum and complement, nor anti-canine globulin had any observable effect on cytotoxicity. The monocytotoxicity bore a temporal relationship to the thrombocytopenia. It is suggested that T lymphocyte activation accompanying ehrlichiosis contributes to pathogenesis of the disease and that the specific immune elimination of parasitized monocytes is antibody independent.

Identification of Ehrlichia canis in East Africa.

Ehrlichia canis, the causative agent of canine ehrlichiosis or tropical canine pancytopaenia (TCP) has been identified in Kenya. Transmission studies to two dogs resulted in signs of ehrlichiosis including marked thrombocytopaenia, pyrexia, reduction in the packed cell volume and the presence of E canis in peripheral blood mononuclear cells.

Ultrastructural observations on Ehrlichia equi organisms in equine granulocytes.

The ultrastructure of the etiological agent of equine ehrlichiosis, Ehrlichia equi, was studied in equine peripheral leukocytes. The organisms occurred within membrane-lined cytoplasmic vacuoles of neutrophils and eosinophils. Ovoid, round, and rod-shaped profiles were observed. From 1 to 33 organisms were present in a thin-section profile of a cytoplasmic vacuole. Many cells contained multiple organism-containing vacuoles. The organisms had a cell wall and plasma membrane, and internally they consisted of electron-dense and lucid areas. A great variation in size was observed. The morphological features were most consistent with agents of the genus Ehrlichia.

Ultrastructure of Ehrlichia canis.

The ultrastructure of Ehrlichia canis was examined in both pulmonary mononuclear cells and in monocytes cultured from an infected dog. The cytoplasmic inclusions, or morulae, of E. canis consisted of a membrane-lined vacuole-containing elementary bodies which varied in size and number. The elementary bodies were bound by two trilamellar membranes. The organism shared morphological properties of both the genus Rickettsia and genus Chlamydia.

Serological diagnosis of tropical canine pancytopenia by indirect immunofluorescence.

An indirect fluorescent-antibody test for detection and titration of antibodies to Ehrlichia canis, the causative agent of tropical canine pancytopenia, has been described. The organism propagated by an in vitro technique in canine blood monocytes served as an antigen in the test. The specificity of the test was revealed by absence of cross-reactivity between the antigen and sera from dogs infected with various common pathogens and specific sera against eight rickettsial species. The accuracy of the test was ascertained by isolation of the organism from reactor dogs located in and outside the United States. Histopathological examination of nine reactor dogs revealed plasmacytosis of meninges and kidneys in eight of them.