BSE and vCJD: Their biology and management
BSE and vCJD: Their biology and management

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BSE and vCJD: Their biology and management

9 Managing the BSE/vCJD episode from May 1990 to March 1996

The discovery of FSE in the domestic cat and TSEs in antelopes of five different species (Section 4) - plus laboratory transmission of BSE to a pig - confirmed the transferability of BSE between species. The ban on SBO was therefore extended from September 1990 to cover all animal feed (including pet food). At the same time, the export of such feed to other Member States of the EU was banned. Nevertheless, the Tyrrell Committee advised that there were no implications for human health. An October 1990 Order brought in new arrangements whereby cattle farmers had to keep records of their animals for 10 years. [D]

Question 47

Bearing in mind the apparently inexorable growth in the number of BSE cases at this time (Figure 1) and the appearance of TSEs in a range of other species, do you think that an even more precautionary approach would have been justified? Are any 'mixed messages' evident in how the episode was being handled? [R D]

Answer

There are contradictions in the introduction of a range of control measures designed to stop the spread of BSE among cattle and to other species, while at the same time insisting that beef was entirely safe for human consumption. There could have been no scientific evidence that BSE posed no health threats to humans. Indeed, there could never be such evidence because it is logically impossible to prove a 'negative'. Strict application of the precautionary principle would therefore suggest that more action ought to have been taken even at this stage. On the other hand, the beef and dairy industries were important for the UK economy and this also had to be borne in mind.

Notwithstanding the various precautions outlined above, it was announced in November 1990 that BSE had been detected in offspring born after the ruminant feed ban was introduced in 1988.

Question 48

What are the implications of this announcement?

Answer

Despite the precautionary control measures that had been introduced up to this point, BSE clearly was still being contracted even by calves that should not have consumed any SBO (and hence PrPSc) in their feed. Either BSE was being transmitted through routes other than contaminated SBO in cattle concentrates or the controls were not operating effectively.

Clearly, it was essential to establish whether the scientific understanding of BSE was incomplete or whether human failings meant that the various precautionary measures that had been introduced were not having the desired effect.

The controls certainly did not always operate as intended. First, a ban might simply be ignored. For instance, if you were running a dairy farm and found that you had some cattle concentrate containing SBO left after July 1988, might you not be tempted to use it - either to avoid waste or because of commercial pressures you were under? Second, accidents happen. If SBO is banned from ruminant feed, but not from feed intended for other animals, there can be genuinely accidental contamination either during manufacture of ruminant feed or on a farm. (Of course, if tissues from the non-ruminant animals to which SBO-containing feed was given were then incorporated into cattle feed, then the cycle of contamination would continue.) [R E D]

Question 49

With SBO banned from ruminant feed in the UK, how would feed manufacturers probably respond? [R E D]

Answer

They would probably still continue to export SBO-containing material provided there was a market for their product. Indeed, they might endeavour to expand this market in an effort to compensate for the loss of their home market. At the time, this would have been perfectly legal even if ethically questionable, given that their product was not considered sufficiently safe for use in the UK.

Even after the EC banned export of SBO to Member States, manufacturers continued to export feed containing SBO to countries outside the EU. However, the Department of Trade and Industry introduced an Order in July 1991 controlling the export of SBO and feed containing SBO to such countries. [D]

In November 1991, it became illegal to use MBM produced from SBO as an agricultural fertiliser. This was designed to address the problem of back-importation - SBO legally exported to continental Europe for use as a fertiliser and then legally re-imported for feed because of the shortage of feed in the UK. [R D]

In March 1992, the use of cattle heads once the skull had been opened and the brain removed was prohibited except in areas that are free at all times from any food intended for human consumption. This was a recommendation from SEAC, which concluded that the measures then in place provided adequate safeguards for both human and animal health. Given the mounting evidence that previous safeguards had not proved adequate, the basis for this reassurance is unclear. Certainly, there appeared to be no new scientific evidence to support it. [R D]

In March 1993, the CMO again made a public statement declaring that beef was safe to eat. [C R D]

Over the next three years, a number of new and amended Orders and Regulations were introduced in the UK, as well as rules that applied throughout the EU. These were all designed to bring the UK epidemic under control, prevent BSE spreading elsewhere, safeguard human health and reassure the public. For example, mammalian protein was prohibited from being fed to ruminants throughout the EU; control of bovine offal was extended to cover the animals' thymus and intestines; TSEs in all species - not just ruminants - were made notifiable diseases; and the spinal cord (plus obvious nervous and lymphatic tissue) had to be removed from bovines over six months old and not used for human consumption. [C R D]

In November 1995, MAFF officially informed SEAC that some abattoirs were ignoring the ban on SBO. [C R D]

Question 50

A 1995 Regulation required that SBO be stained blue (Figure 14). What does this requirement, which effectively removed decision making from the local level, suggest? [C]

Answer

Without such staining to make it obvious, SBO might be getting into food for human consumption. The blue coloration served to warn workers in abattoirs that they were dealing with banned materials and also that processing it would be pointless as nobody would choose to eat blue food.

Figure 14
Courtesy of Foods Standards Agency, © Crown Copyright. ©
Courtesy of Foods Standards Agency, © Crown Copyright.
Figure 14 Blue-stained SBO (specified bovine offals)

At about this time, SEAC turned its attention to the possible dangers posed by the removal of so-called mechanically recovered meat (MRM) from the spinal column. Special equipment was used to obtain almost every last scrap of usable meat from a carcase for inclusion in cheaper meat products. In the process, there was a possibility that small amounts of nervous tissue contaminated with PrPSc might end up in food for human consumption and thus pose a risk of transferring BSE to humans. The use of bovine vertebral columns in the manufacture of MRM, the use of MRM in food for humans and the export of bovine MRM to other EU countries were all prohibited by a December 1995 Order. [R D]

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