[Testing the live cultural vaccine against theileriasis].
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Various developmental stages of Hyalomma anatolicum were subjected to a range of doses of 60Co radiation from 0-10 000 R, and their subsequent development was observed. Some of these ticks were infected with Theileria annulata. Doses of 2000 R and over prevented all but a very limited development of ticks. After 1000 R a proportion of exposed individuals continued development in a near-normal manner. Lower doses had proportionately less effect. 1000 R to ticks infected with T. annulata failed to prevent transmission of typical theileriasis to calves.
The use of drugs in domestic animals is dominated by considerations of cost-effectiveness and profitability. They are extensively used against coccidial infections of poultry where they are an important factor in intensive husbandry. Ionophore antibiotics, which dominate this field, may have applications in ruminants. Imidocarb is of therapeutic and prophylactic value against babesial infections anf there are new prospects for control of theileriasis. Effective drugs for the control of African trypanosomiasis are limited and attention is being given to alternative uses of available compounds.
A complement-fixation (CF) antigen which has been prepared from Theileria infected erythrocytes is capable of reacting to specific serum antibodies of deer acutely infected with Theileria. No sera from 17 deer known to be free of Theileria infection reacted positively to the CF test. Of 35 tests on sera from 12 infected deer having a parasitemia of 2% or less and no accompanying anemia, only 10 (29%) were positive, 2 (6%) were suspicious, and 23 (66%) were negative. Of 65 tests on 8 acutely infected deer, 49 (75%) were positive, 4 (6%) were suspicious and 12 (18%) were negative. Of the 8 deer in which acute theileriasis occurred all reacted to Theileria antigen at one time or another.A significant correlation was found between CF titers and the degree of parasitemia in acute infections. Rabbits were hyperimmunized using erythrocytes from either normal or Theileria infected deer. Reciprocal absorption of the hyperimmune sera with Theileria and normal erythrocytic antigens demonstrated the presence of antibodies specific for Theileria.
A review of 'piroplasmosis' (a collective name tick-borne protozoan forms of disease of the blood (babesiasis, theileriasis) as well as rickettsial forms (anaplasmosis), written by De Blieck and published in 1916, is compared with the present state of our knowledge. Considerable progress has been made in classifying the causative agents. Moreover, the situation in the Netherlands has become much clearer. However, as regards the situation in the tropics, progress in control is rather limited and these forms of disease continue to be of major economic importance. The use of ascaricides is becoming increasingly confronted with problems and, in particular conditions, the use of cattle characterised by a considerable genetically acquired ability to produce an immune response to ticks is growing. In addition, it is hoped that it will be possible to immunise animals both against ticks and against tick-borne disease using characterised antigens produced by modern biotechnological methods in the future. Finally, a warning note is sounded that the active role of the faculty of veterinary science in the field of tropical veterinary medicine could well be reduced in the near future as a result of economies and changes of structure.
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Cytotoxic cell lines specific for cells infected with the protozoan parasite Theileria parva were generated in vitro by repeated stimulation of peripheral blood mononuclear cells (PBMC) from immune animals with autologous parasitized cells from continuously growing cell lines. In PBMC of 5/7 immune animals tested, maximal levels of killing (80-100%) were obtained at effector to target ratios of 10/1 following 3 to 5 stimulations. No killing of uninfected lymphoblasts was observed. Cytotoxic activity was contained in the BoT4- lymphocyte population. The results of analyses of cytotoxicity on panels of target cells of diverse major histocompatibility (MHC) phenotypes indicated that the effectors were restricted by class I MHC antigens. Only autologous targets and allogenic targets sharing one or other bovine lymphocyte antigen A locus-encoded specificity with the cytotoxic cell line were killed. In addition, two of the three cytotoxic cell lines, when tested on targets infected with different parasite stocks, exhibited a high degree of specificity for the stock used for immunization and stimulation of the cultures. The capacity to generate highly cytotoxic, MHC-restricted effectors from peripheral blood was dependent on the immune status of the donor animals. This was confirmed by comparing cytotoxicity generated from the same animal before and after immunization using the same autologous infected cell line as a stimulator. These results indicate that these effector cells are analogous to the cytotoxic cells detected in vivo in cattle undergoing immunization or challenge with T. parva.
The Muguga and Marikebuni stocks of Theileria parva differ on the basis of cross-protection and in their schizont antigen profile determined with a panel of parasite-specific monoclonal antibodies. The phenotype and specificity of six cytotoxic T cell clones generated from an animal immunized against T. parva (Marikebuni) were investigated. All six clones had the BoT2+ BoT4- BoT8+ phenotype, were dependent on both specific antigen and T cell growth factor for proliferation and were restricted by determinants on class I major histocompatibility complex molecules. The clones killed target cells infected with either the Muguga or Marikebuni stocks of the parasite; the target cell lines tested included T cell clones which were infected in vitro with the two parasite stocks and subsequently recloned. The specificity of these cytotoxic T cell clones contrasts with that of T cell clones generated previously from animals immunized against T. parva (Muguga), in that the latter were specific for target cells infected with the Muguga stock of the parasite. Moreover, one of the clones generated against T. parva (Marikebuni) was restricted by the same major histocompatibility complex molecule as the Muguga-specific T cell clones. The difference in parasite strain-specificity between the two sets of clones appears to reflect the capacities of the two parasite stocks to cross-protect, since animals immunized against T. parva (Marikebuni) are protected against challenge with T. parva (Muguga) whereas a proportion of animals immunized with T. parva (Muguga) are susceptible to challenge with T. parva (Marikebuni). Another difference between the two sets of T cell clones was that those generated against T. parva (Marikebuni) only killed a proportion of cells of a given cell line in a 4-h cytotoxicity assay, whereas Muguga-specific T cells invariably kill the majority of cells. However, despite this partial killing, the clones markedly inhibited growth of parasitized cell lines when cultured with them for a period of 5 days.