'Mad cow' probe: fresh fears

LONDON - British Government advisers on "mad cow" disease are to investigate fresh evidence that cattle can be badly infected with bovine spongiform encephalopathy (BSE) for years without showing symptoms.

It is now claimed that BSE may "jump" from one species to another more easily than had been thought. That could mean other forms of meat could infect people with the disease.

New research has shown that certain strains of prions, the infectious agents thought to cause BSE, can infect laboratory mice, although the animals never develop the disease.

The findings indicate that BSE can exist in a subclinical form, where high levels of infectious agent are present in an animal but fail to result in symptoms. The same may be true of variant Creutzfeldt Jakob Disease, vCJD, the human equivalent of BSE.

Subclinical disease is different from the incubation period for BSE, when relatively low levels of the prion agent begin to build up and spread within an infected animal, eventually to cause symptoms.

Professor Peter Smith, the acting chairman of the Government advisory body, the Spongiform Encephalopathy Advisory Committee, said the latest findings, published in the Proceedings of the National Academy of Sciences, are of "considerable interest" and will be discussed in detail when it meets on September 29.

The research, by scientists at the Medical Research Council's prion unit, based at St Mary's Hospital, London, demonstrated that mice remain healthy when infected with large amounts of prions from infected hamsters.

Previous research had shown that mice never develop the disease when injected with hamster prions, leading scientists to believe that there was a large "species barrier" protecting mice from this source of infection.

Furthermore, when infective material from the symptomless mice was subsequently injected into other mice, these animals did develop symptoms, suggesting that a new strain of prion had been created.

John Collinge, the leader of the research team, said the results showed that just because a species appeared resistant to BSE, did not mean they were free of infection.

He said sheep, pigs and poultry - as well as cattle - exposed to BSE via animal feed might have developed the subclinical form. This would mean animals thought to be incapable of acquiring BSE could theoretically pass the disease to humans.

Collinge said present measures to protect the public from BSE did not need to be changed, but he wanted to see a national system in Britain of testing brains of cattle and other species exposed to BSE for signs of prion infection.

- REUTERS, INDEPENDENT