The sanity of the men from the ministry is the only thing at risk from the dissection of sheep's eyes

The prohibition by the Ministry of Agriculture, Fisheries and Food of the use of sheep's eyes for dissection by science students in colleges has serious implications: not so much for any human health risk as for the sanity of the ministry.

First, let us suppose that there is a theoretical risk from manipulating sheep's eyes - what might be deduced from this for the safety of lamb? About 300 cases of sheep scrapie are reported annually in the United Kingdom, predominantly in ewes aged three to four years at death. The disease has been well researched, both in sheep themselves and after its transfer to rodents. In the 18 months prior to death, infectivity is found in many organs, although the greatest amount is in the brain. With this group of disease agents, called transmissible spongiform encephalopathies, organs as diverse as lungs, muscle, bones and nerves have been found to be infectious.

This means that if MAFF really does believe that there is a risk from tiny fragments of sheep's eyes or ocular fluid somehow entering the human body through cuts or inhalation, then the logical assumption that follows is that sheep products generally are hazardous and should not be eaten. Any attempt to routinely dissect out in the abattoir the presumed most infectious organs such as spinal cords would be nigh impossible in practice.

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So is there any evidence that sheep scrapie can infect people? Virtually none. The human condition that sheep scrapie might cause is sporadic Creutzfeldt-Jakob disease. But the incidence of this illness does not correlate with that of sheep scrapie. For example, sporadic CJD occurs in Australia and New Zealand, but sheep scrapie has not occurred there for decades.

For the development of a spongiform disease the mammalian host's own DNA is required, and this therefore influences the nature of the resultant infectious agent or prion. It is reasonable to assume, therefore, that the lack of infectivity of scrapie for mankind is determined by the sheep genome. This means that even if BSE - so-called mad cow disease - were to spread from cattle to sheep under natural conditions (and it can by experiment) there would be no certainty - probably the reverse - that such an infection would affect the human population. The expectation that BSE might infect man was derived from the knowledge that BSE is distinct from sheep scrapie in three ways: in the physical properties of the prion; the epidemiology of the disease; and the failure in experiments of scrapie to induce BSE in cattle. The threat to humans from BSE has now been confirmed.

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Why then has MAFF prohibited the use of sheep's eyes for dissection? Also why has the European Agriculture Commissioner requested that sheep brains be excluded from the food chain and why have some countries called for a ban on British lamb?

I believe that these stances have been entirely generated by the actions of the British government. For years Government spokespeople told the world that BSE was caused by the incorporation of sheep offal into cattle feed; that BSE was bovine scrapie, and because man is not vulnerable to scrapie in sheep, man would also not be vulnerable to its equivalent in cattle. If this claim was made to protect the cattle industry it seems that, regrettably, many people believed it.

European countries now know that BSE can cause CJD and, logically, because they have been told that BSE was caused by sheep scrapie, they believe that scrapie also is a hazard.

In stopping dissection of sheep's eyes MAFF can be seen to be making a gesture to protect the public without damaging the sheep industry. There are other examples of this type of doublethink. Since 1989 the Department of Health has advised pharmaceutical companies not to use gelatine (made from cattle bones) from regions where BSE was prevalent, but there were no controls over gelatine in food. Also in 1989, just six cattle organs were excluded, in theory anyway, from the food chain.

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How can anyone believe that infectivity will be confined to the brain, spinal cord, spleen, thymus, tonsils and intestines? The vertical transfer of BSE, for example, has occurred via blood. Even as recently as March 1996 MAFF claimed that the whole carcass of cattle aged 30 months or more might be hazardous, but cattle aged 29 months were safe. In my opinion there are no scientific facts to support this.

Throughout the BSE crisis, MAFF has taken the minimum action required to reassure the public, and therefore avoid the costly and damaging effects of total herd replacement. Now some scientists suggest that BSE will spontaneously disappear by the year 2001. True, it may appear to do so, with farmers facing the threat of whole herd slaughter if further cases are reported, and with the slaughter of animals over 30 months reducing the clinical phase of the disease further. However, spongiform diseases are well known to spread horizontally, vertically and via the environment. MAFF has always maintained that BSE is acquired around birth. Assuming this is the case, none of the actions taken so far is relevant to its eradication and the problem of sheep's eyes seems to be nothing but a cynical diversion.

Richard Lacey is professor of medical microbiology at Chapel Allerton Hospital, Leeds.