New strains of the prion that causes bovine spongiform encephalopathy (BSE) have been reported by scientists in Italy and Japan.
Until now, all known cases of BSE have been caused by the same prion strain. But experts have long suspected that additional strains of BSE might be lurking in cattle, which they fear could propagate new human diseases, as happened in the 1990s outbreak of variant Creutzfeldt–Jakob disease.
The new strains are readily detected by existing tests for BSE. The researchers identified them from brain samples using a technique called the western blot, which produces a series of bands that represent the prions present. In the case of the new strains, the western blot showed a different pattern of bands from conventional BSE. Researchers remain concerned that if prion variants continue to emerge, some of them may escape detection by existing tests.
On 6 October, Morikazu Shinagawa of the National Institute of Animal Health in Tsukuba, Japan, reported that a bullock born there had tested positive for BSE, and that the characteristics of the prion were different from those of classical BSE. Two days later, Maria Caramelli at the National Reference Centre for Animal Encephalopathies in Turin, Italy, reported that two of 110 cows that had tested positive for BSE involved similarly distinctive prions.
In both cases, the prions were found during abattoir sampling of symptom-free animals. The Japanese and Italian scientists have yet to confirm whether the two strains are identical.
“What we have is definitively a new variant, but it was detectable by a conventional rapid test, so there is no immediate risk of a new epidemic,” says Caramelli, who presented her work at the International Prion Conference in Munich last week.
“There has never been good reason to believe that there should only be one variant in cattle,” says Adriano Aguzzi, a prion expert at the University Hospital in Zürich, who points out that several strains of spongiform encephalopathy have been found in sheep and in humans. “It will be interesting to find out if the new prion variants were introduced in cattle feed, or if they spontaneously emerged in the cattle as a result of a gene mutation,” he adds.
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