New BSE 'risk' assessed

BSE may be able to jump the 'species barrier'

The UK Government's medical advisers are to consider the findings of a team of scientists that sheep, pigs and poultry could theoretically pass BSE on to humans.

Scientists investigating the disease are warning that it may infect animals other than cattle without showing any symptoms.

In a paper published on Monday, scientists led by Professor John Collinge say there could be "important public health implications".

The possibility of further action to protect public health is to be examined by a body of experts advising the government on mad cow disease.

79 cases of variant CJD have been recorded so far

Members of the Spongiform Encephalopathy Advisory Committee (SEAC) are to consider the findings at their next meeting on 29 September.

Professor Peter Smith, acting chairman of SEAC, said: "It is not clear that the new findings indicate that additional controls should be considered with respect to protecting human or animal health."

The research is published in the journal Proceedings of the National Academy of Sciences.

Prof Collinge's team, from the Medical Research Council Prion Unit based at St Mary's Hospital, west London, took a closer look at the "species barrier" which most experts believe makes it difficult for BSE-type diseases to spread between different species of animal.

Hamster scrapie

BSE belongs to a wide family of "prion" diseases which also include scrapie in sheep and both "classical" and "variant" CJD in humans.

We should not assume that just because one species appears resistant to a strain of prions they have been exposed to, that they do not silently carry the infection

Professor Collinge

They are thought to be caused by abnormal prion proteins which create deadly plaques in the brain.

Variant CJD, which first emerged in 1996, is now known to be BSE in a human guise. It is thought to have spread to the human population through people eating contaminated beef products in the 1980s.

A total of 79 cases of variant CJD have been recorded so far.

The MRC scientists infected laboratory mice with a form of hamster scrapie called Sc237.

Ordinary mice have always been thought to put up an effective barrier against this disease.

As expected, the mice showed no apparent signs of illness. On closer inspection, however, the researchers found that they had high levels of potentially lethal abnormal prions in their brains.

The researchers also showed that this subclinical infection could easily be passed on when injected into healthy mice and hamsters.

The fear is that what is true for hamsters and mice may also be true for cattle and other animals with BSE, and humans with CJD.

The results also raised another fear, of CJD being transmitted from seemingly healthy hospital patients via surgery equipment.

Abnormal prions

A more comforting implication was that since animals could harbour high levels of infectiousness without developing clinical signs, it was likely that abnormal prions were not on their own highly neurotoxic.

Prof Collinge said: "These results suggest that we should re-think how we measure species barriers in the laboratory, and that we should not assume that just because one species appears resistant to a strain of prions they have been exposed to, that they do not silently carry the infection.

"This research raises the possibility, which has been mentioned before, that apparently healthy cattle could harbour, but never show signs of, BSE."

At present no cattle over the age of 30 months are allowed to enter the human food chain, and high-risk tissue such as the brain, spinal cord and spleen is banned from meat products.

Since 1996, it has been illegal to give cattle feed that contains cow and sheep remains.