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Fading immune protection in farmed animals may present a problem, particularly in free-ranging animals in nomadic and transhumant pastoral systems, where animals are not readily available for large-scale blanket vaccination programmes. Two veterinary examples of fading immune protection are discussed: rinderpest and foot-and-mouth disease (FMD). Both are devastating viral diseases of cattle that have a huge impact on the farming economy. Both diseases can be controlled by vaccination, although the post-vaccination immunity afforded by the rinderpest vaccine is markedly different from that induced by FMD vaccines. These differences may in part explain the respective advancement of international eradication campaigns: while global eradication of rinderpest is imminent, FMD viruses are still actively circulating in many parts of the world.

The presence, type, and extent of cellular death in lymphatic tissues of cattle experimentally infected with rinderpest virus strains of different virulence was investigated morphologically. Cells with DNA strand breaks were identified in histological sections of palatine tonsil, spleen, and mesenteric and mandibular lymph nodes by the TUNEL (terminal desoxynucleotidyl transferase-mediated dUTP nick end labelling) assay. In addition, representative samples of lymphatic tissues were examined by transmission electron microscopy. The results indicated that cellular disassembly in lymphatic tissues was caused by both apoptosis and oncosis. Cells with DNA strand breaks were observed in follicular and parafollicular areas of lymphatic tissues and their numbers were determined. A significant correlation was found between the number of TUNEL-positive cells and viral virulence. These results suggest that, in addition to oncosis, apoptotic cellular death in lymphatic tissues contributes substantially to the pathogenesis of rinderpest.

Summary The pathogenesis of infection with the L-strain of rinderpest virus (RPV) in rabbits was investigated. Of several lymphoid tissues examined, those associated with the gut showed the most marked virus growth. The virus titres were maximal 4 days after inoculation but had declined at day 6. The distribution of viral antigen was examined immunohistochemically with the recently established anti-rabbit CD5 monoclonal antibody (MoAb), which is a pan-T-cell marker, and the anti-RPV-nucleoprotein MoAb. The virus antigen was localized in the CD5+ area at the initial stage of infection but spread to all areas of the lymphoid tissues at the later stages. By flow cytometric analysis with both rabbit CD5 and CD4 MoAbs, a decrease of the CD4+ and CD5+ subpopulations was observed in the spleen and mesenteric lymph nodes.

Summary An investigation into the viability and potency of freeze-dried lapinised rinderpest vaccine is recorded. It is emphasized that because of the absence of a marked thermal reaction in the majority of cattle inoculated with lapinised vaccine,,great care is required to ensure that potent material is inoculated.