The principle sites of infectivity in mammalian species carrying TSEs are in the brain and spinal cord. To reduce the risk of transfer of TSE infectivity from meat to man, these tissues have been excluded from entering the food chain. However, conventional slaughter and butchery practice could enable these tissues to cross-contaminate the meat and meat plant environment. Risks are different in different species, bovine carcasses being conventionally split down the median sagittal plane at the end of dressing, thus exposing the spinal cord, whilst the majority of young sheep carcasses are despatched in entire form from the abattoir, and currently contain the spinal cord.
Cross-contamination is important because of the increasing public concern over food safety; and it may be direct, that is between constituent parts of a carcass and its meat, or indirect, that is from a source on one carcass to another via some route involving the environment, operator or implement.
In order to minimise cross-contamination, it is necessary to determine the routes through which it could occur, and the importance of each of the routes. Through monitoring CNS dispersion under research and commercial abattoir conditions, it is anticipated that best practices and critical points in existing procedures can be identified.
Protein antigen-based (ELISA) assays will be used to monitor cross-contamination of carcasses, equipment and abattoir environment (including atmospheric) with CNS material during conventional slaughter, dressing and butchery of cattle and sheep, in order to identify critical practices. Based on the results of these studies, changes to conventional methods will be tested under experimental conditions to ascertain whether cross-contamination can be reduced. Concurrently, innovative equipment (particularly saws and vacuum devices) will be developed and tested for their ability to reduce or eliminate cross-contamination. A set of guidelines for avoidance of CNS cross-contamination in the meat industry will be drafted for presentation to the EC.
Robust, sensitive assays have been developed for the detection of syntaxin 1-B, GFAP, S100 and PrP as means of quantification of CNS material with a simple sampling protocol that gives good reproducibility in the assays.
Penetrating captive bolt stunning has been shown to result in neural embolism -potentially a significant cause of cross-contamination of meat with brain material.
CNS contamination of carcasses, equipment and atmosphere, in both experimental and commercial abattoirs, has been measured. There is significant CNS contamination of the interior of the carcass during splitting; this is concentrated on the cut surfaces and is not removed by washing. There is little contamination of the abattoir atmosphere. Consequently, abattoir workers are not perceived to be at risk from inhalation of CNS material. Transfer of CNS material onto adjacent abattoir equipment is also minimal.
Prototype equipment has been developed. An oval saw for removal of the spinal column intact shows considerable promise. The prototype sheep version removes the column in 6 seconds, but the prototype cattle version required a more powerful motor. However, this saw is only likely to be adopted if driven by legislation.
Further work to extend the sampling throughout other European countries has been completed.
M.H. Anil, S. Love, S. Williams, A. Shand, J.L. McKinstry, C.R. Helps, A.E. Waterman-Pearson, J. Seghatchian & D.A. Harbour. 1999. Potential contamination of beef carcases with brain tissue at slaughter. Vet. Rec. 145: 460-462.
Daly, D.J., Prendergast, D.M., and Sheridan, J.J. 2000. Contamination of carcass meat and the abattoir environment with central nervous system material. Irish Journal of Agriculture and Food Research, 39 (1) :156.