M03010 Further studies on the transmissibility of BSE to pigs

Vacuolation, spongiosis, spongiform change or micro-cavitation are synonymous terms used to describe the light microscopic appearance of pathological optically empty spaces in histological sections of the central nervous system. Similar changes can be produced in histological preparations by autolysis and tissue processing artefacts (Wells and Wells, 1989). The occurrence of neuronal vacuolation, that is vacuoles within neuronal perikarya in certain neuroanatomical locations, as an incidental finding at post-mortem examination in the brains of domesticated animals, has been recorded previously and reviewed in relation to its potential to confound the histopathological diagnosis of transmissible spongiform encephalopathies (TSE) (Wells and McGill, 1992; GavierWiden et al., 2001). Although such occasional strictly localised neuronal vacuolation, especially in the dorsal nucleus of the vagus nerve, has been noted in pigs as an incidental finding in diagnostic submissions in the past (G. A. H. Wells, unpublished), a naturally occurring transmissible spongiform encephalopathy (TSE) has not been described in the pig. The observations of apparently incidental vacuolar changes also in neuropil (particularly that of the rostral colliculi) of the brains of exposed and control pigs in studies of the parenteral (project SE1816) and oral (project MO3004/SE1817) transmissibility of bovine spongiform encephalopathy (BSE) (Ryder et al., 2000; Wells et al., 2003) was therefore of interest in this context and because it does not seem to have been recorded previously in the pig or in other species.