Bits of brain taken from dairy farmers who recently died of Creutzfeldt- Jakob disease - the human equivalent of mad cow disease - are being injected into laboratory mice in what scientists hope may be a definitive experiment to show whether BSE can spread to humans.
Brains from infected cattle have already been "passaged" through mice which catch the murine (mouse) equivalent. According to Dr Sheila Gore, from the Institute of Public Health in Cambridge, tissue infected with bovine spongiform encephalopathy produces a distinctive pattern of damage to the mouse brains. She said: "If that pattern were seen when material from brains of CJD farmers is used it would suggest very strongly that BSE had come into humans. It would prove the link."
Public concern about a possible link between the bovine and the human diseases has recently been heightened following the deaths of four farmers and two young people from CJD. But it will take at least two years before the results of the experiments in mice are known.
In an article published in today's issue of the British Medical Journal, Dr Gore warns that the "cases of Creutzfeldt-Jakob disease in farmers and young adults are more than happenstance. They signal an epidemiological alert to investigate intensively possible exposures - farm related and dietary".
Dr Gore said yesterday: "There is some urgency to this. It would be negligent if we did not follow these things up." She stressed, however, that she was not saying humans had been infected: "We don't have proof that BSE has come into humans. We do have an unusually high number of occurrences in people who have worked with adult cattle so that we want to look at occupational exposures."
Cows are believed to have caught BSE by eating cattle meal infected with sheep scrapie, following changes around 1982 in the way the rendering industry treated offal and other wastes.
From the first certified case in 1986 to the middle of this year, the disease has been confirmed in more than half of dairy herds and 15 per cent of beef suckler herds. Dairy farmers are therefore at risk of occupational exposure to the agent that causes the disease, if BSE is transmissible to humans.
Dr Gore added: "I don't know what the dairy farmer source may be. Farmers do apparently eat cattle cake - it's rich in protein." If farmers did eat cattle cake in the early 1980s it would have been contaminated with BSE infected material. Dr Gore pointed out that the incidence of CJD is much higher among dairy farmers than it is for farmers as a whole and that this is true not just in Britain but in other European countries.
It is possible that these countries have had infected but not affected cattle - calves exported from the UK for veal for example might be infected but would be slaughtered before the disease became apparent.
Dr Gore suggested that it would be worth studying CJD among farmers in countries such as the US, New Zealand, and Australia where there has essentially been no incidence of BSE to see if the trend holds that there is a higher incidence among dairy farmers than for farmers as a whole.Reuse content