A different form of abnormal proteins which cause BSE in cattle has been found in the youngest ever case of the disease in a bull in Japan.
The discovery of a different form of the disease in an animal aged 23 months has rocked current scientific thinking and could have major repercussions for the beef industry worldwide.
It may also have implications for human health as BSE has been linked to the variant Creuzfeldt-Jakob disease (vCJD) in humans which has killed 130 people in Europe, most of them in Britain where the disease was first identified.
The World Organisation for Animal Health, the OIE in Paris, has described the Japanese case as "atypical BSE".
The animal, a 23-year-old Holstein bull from Ibaraki, north of Tokyo, was confirmed as having the disease on 6th October last.
Experts who examined the brain of the animal said tests had showed that the abnormal proteins causing the disease were of a different type to those previously reported.
Scientists there claimed that Italian experts had reported two cases in Italy at a recent academic conference in Germany that showed similar test results to those of the Japanese animal.
The Japanese officials said that the Italian cases showing the new variants had been discovered in 2002 but were not reported until details were given at a recent international conference.
Apart from the possibility that there may be a new variant of the disease, the confirmation of BSE in an animal under 24 months has challenged conventional scientific thinking.
The belief has been that the disease has a long incubation period of around two to eight years. In addition, the assumption was that young animals were unlikely to have the disease.
Based on that assumption, the European Union decided that it was not necessary to test animals under 30 months intended for human consumption.
Prof Patrick Cunningham, of the department of genetics, Trinity College, Dublin, said it appeared from the reports that the structure of the BSE infection in the Japanese animal was different. The finding had implications for those who believed the disease was unlikely to happen in animals under 30 months.