The problems caused by tick and tick-borne diseases for livestock particularly cattle on the African continent are described and discussed. The control of ticks and tick-borne diseases must receive high priority in Africa with regard to both research and control application because of their widespread distribution in areas of high livestock potential and productivity. The conventional methods of tick and tick-borne disease control are discussed and are found to be inadequate in the conditions prevailing in Africa. Methods of integrated control are suggested and discussed in light of recent development in control methods and those still under development. Any one of these methods may not be adequate to control the problem on its own but when several of the methods are combined an economic and robust integrated control is likely to result. Encouragement is given to attempt this approach in Africa to solve what must be the largest animal health problem of livestock remaining in the world.

The MHC restriction and parasite strain specificity of cytotoxic cells elicited in a group of Theileria parva (Muguga)-immunized cattle following homologous challenge, were investigated. The cytotoxic cells were specific for parasitized target cells and in 9 of the 10 animals examined, they were clearly genetically restricted. Cytotoxicity could be inhibited by monoclonal antibodies (MoAb) to class I MHC molecules but not by MoAb to class II molecules, indicating that a large component of the response was restricted by class I MHC determinants. Low levels of inhibition of cytotoxicity were also obtained with a MoAb to the T-cell subset marker BoT8, suggesting that at least part of the response was mediated by BoT8+ lymphocytes. When cytotoxic cells from individual cattle were assayed on panels of parasitized target cells, there was a close correlation between susceptibility of the target cells to lysis and sharing of BoLA-A locus-encoded specificities with the effectors. This observation, taken together with the knowledge that within several of the sets of BoLA-A-matched targets the relevant BoLA-A specificities were on different MHC haplotypes, indicated that the responses were restricted predominantly by BoLA-A products. In individual cattle there was a striking bias in the restriction of the response to one or other BoLA-A specificity. Among the six specificities represented, responses restricted by w6, w8 and KN18 consistently predominated over responses restricted by w7, w10 and w11. In the three cattle tested for parasite strain specificity, two showed complete specificity and one partial specificity for cells infected with the parasite stock used for immunization, T. parva (Muguga).

Clinical and immune responses were determined for guinea pigs infected with different doses of foot-and-mouth disease virus (FMDV) type A12, strain 119, administered by different routes. Vesicles developed on the tongue or heel pad 1 day after these areas were intradermally inoculated with FMDV. However, vesicles did not develop on the feet and tongue until 3 to 4 days after the intradermal inoculation of FMDV in the flank skin or after intracardiac or subcutaneous inoculation. Infected guinea pigs developed neutralizing antibody, immediate skin reactivity of the Arthus type (4 h), and delayed skin reactivity. In addition to a delayed skin response, the presence of a cell-mediated immune response to FMDV was shown by the specific production of macrophage migration inhibition factor by peritoneal exudate cells in response to FMDV. Kinetic studies showed that neutralizing antibodies were detected at 3 days postinfection, and Arthus and delayed skin reactivity were detected at 4 days postinfection. Some guinea pigs developed either mild or subclinical infections. Regardless of the dose of infectious virus, the route of inoculation, the severity of disease, or the time of clinical onset of disease, infected guinea pigs developed similar immune responses.

Histocompatibility may be a barrier to the infection of cattle when Theileria parva parva-infected tissues or in vitro cultured macroschizont-infected lymphoblastoid cell lines are used for immunization. By inoculating 10(3) and 10(5) infected cells into autologous recipients infection was achieved and immunity engendered. Cell lines inoculated into BoLA matched recipients did not produce patent infections but some recipients developed antibodies to the parasite and 3/5 were immune to challenge. No evidence of infection or immunity was found in BoLA half matched or mismatched cattle. This result suggests that there is an histocompatibility barrier to infection using T. p. parva-infected lymphoblastoid cells.

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