Jugular venous emboli of brain tissue induced in sheep by the use of captive bolt guns

Frequency of Brain Tissue Embolism Associated with Captive Bolt Gun Stunning of Sheep

In accordance with controls instituted to protect the consumer from meat potentially infected with bovine spongiform encephalopathy (BSE), brain tissue emboli caused by the use of captive bolt gun (CBG) stunning have been identified as a potential public health risk that requires further investigation. As the natural occurrence of BSE in sheep remains uncertain we have investigated the frequency of brain tissue embolism associated with stunning by two types of CBG that are in commercial use in the United Kingdom. Blood samples collected from sheep following stunning were analysed by ELISA as well as by a combination of microscopy and immunocytochemistry. The combined positive results from each method of sample analysis were used to determine the frequency of brain tissue embolism in the sample population. The frequency of brain tissue embolism was found to be 23% in sheep stunned with a cartridge-activated CBG (95% confidence interval of 15.8-32.2%) and 14% in those stunned with a pneumatically activated CBG (95% confidence interval of 8.5-22%). The frequency of brain tissue embolism associated with the use of CBG stunning may represent a significant source of carcass contamination with brain tissue.

Dissemination of brain emboli following captive bolt stunning of sheep: capacity for entry into the systemic arterial circulation

The epidemic of bovine spongiform encephalopathy in the United Kingdom and the recognition of a variant of Creutzfeldt-Jakob disease prompted revision of the guidelines for slaughter of cattle and sheep to prevent contamination of the edible parts of the carcass with central nervous system tissue. We previously showed that captive bolt gun stunning, which is routinely used for the slaughter of cattle and sheep, causes entry of fragments of central nervous system tissue into the jugular vein. To determine whether such tissue can traverse pulmonary capillaries to enter the systemic circulation, we introduced small volumes of brain tissue that had been disrupted by stunning with a captive bolt gun into the jugular vein of sheep sent for slaughter. We examined aortic blood samples by immunocytochemistry for neurofilament and S100 proteins and by enzyme-linked immunosorbent assay for glial fibrillary acidic protein and found fragments of neurofilament- and S100-immunopositive central nervous system tissue in samples from 2 of 11 sheep and elevated glial fibrillary acidic protein in 6 sheep. Our findings suggest that central nervous system tissue that is dislodged during routine captive bolt gun stunning and slaughter of sheep can enter the systemic arterial circulation and that, in some cases, this method of slaughter of an animal infected with bovine spongiform encephalopathy would be likely to contaminate edible parts of the carcass with infective material.

The use of a marked strain of Pseudomonas fluorescens to model the spread of brain tissue to the musculature of cattle after shooting with a captive bolt gun

AIMS

The aim of this study was to use a marked strain of Pseudomonas fluorescens to model the spread of central nervous system (CNS) tissue in cattle following captive bolt stunning.

METHODS AND RESULTS

The marked organism was introduced by injection through the captive bolt aperture immediately after stunning and was subsequently detected in a wide range of derived tissues, including blood, organs, and the musculature of the entire forequarters of test animals. This was dependent on the use of high concentrations of the organism that were recovered sufficiently and rapidly to minimize the bactericidal properties of the circulatory system. These results suggest that a marked organism could potentially be used to model the effects of captive bolt stunning on the dissemination of CNS tissue from the brain.

CONCLUSIONS

These results indicate that current commercial methods of captive bolt stunning may induce widespread and significant mobilization of CNS tissue within beef carcasses. This may lead to the widespread dissemination of such materials within meat destined for human consumption.

SIGNIFICANCE AND IMPACT OF THE STUDY

In the absence of rapid, simple and sufficiently sensitive methods for the direct detection of prion in commercially slaughtered animals, marked organisms can provide useful models in studies of the dissemination kinetics of prion disease in captive bolt stunned animals.

Dissemination of central nervous system tissue during the slaughter of cattle in three Irish abattoirs

Sponge samples were taken from the carcases, meat, personnel and surfaces involved in stunning, slaughter and dressing/boning activities at three abattoirs, and from retail beef products. The samples were examined for the presence of central nervous system (CNS)-specific proteins (syntaxin 1B and/or glial fibrillary acidic protein (GFAP), as indicators of contamination with CNS tissue. Syntaxin 1B and GFAP were detected in many of the sponge samples taken along the slaughter line and in the chill rooms of all three abattoirs; GFAP was also detected in one sample of longissimus muscle (striploin) taken in the boning hall of one of the abattoirs but not in the other two abattoirs or in retail meats.