• AFP-JIJI, Kyodo

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Researchers believe they have found the cause of mad cow disease, though on Wednesday they stressed the need to maintain precautionary measures to avoid a potential re-emergence of the illness.

Several hypotheses have been put forward over the cause of bovine spongiform encephalopathy, a neurodegenerative disease that was dubbed “mad cow disease” when it first appeared in the 1980s in the United Kingdom.

However, to date none has been verified as accurate.

The illness belongs to a family of ailments involving misfolding proteins that are known as prions. These also exist in other diseases, such as scrapie in sheep and Creutzfeldt-Jakob disease in humans.

Researchers injected a scrapie variant into mice, producing the prion of bovine origin following genetic manipulation.

This allowed them to show not only that the illness had the ability to jump from one species to another but that the transmuted mice developed mad cow disease, according to an article in the Proceedings of the National Academy of Sciences.

The genetically modified mice are “a very good model, which works well in terms of knowing what would happen if one exposed cows to those prions,” said Olivier Andreoletti, a researcher with the French National Institute for Agronomic Research (INRA), which led up the study.

The results are explained by “the presence of quantities of classic mad cow disease” in unmanipulated form in the scrapie-variant prions that were injected, INRA stated.

“For the first time, these data bring an experimentally underpinned explanation to the appearance” of mad cow disease in the U.K. in the 1980s.

The disease then spread in cattle across Europe, North America and numerous other countries. The process was aided by the animals’ consumption of foodstuffs that included parts from the carcasses of animals that had been hit by the ailment.

Contact with products from infected cattle led to humans becoming infected with the prions that cause Creutzfeldt-Jakob disease.

From the 1990s, Europe introduced a slew of measures to counter the spread of the illness, including banning cereals mixed with animal parts, tougher surveillance of cross-contaminations and destruction of the highest-risk tissues, thereby eventually bringing the spread under control.

“These measures are still in place — but they are very expensive, leading in some quarters to calls for their elimination and “to resume recycling of good quality proteins” rather than throwing them away in what might be an alternative to soy imports, Andreoletti observed.

He added, however, that any recourse to “nonvirtous practices” risks allowing the disease to re-emerge.

Japan placed a blanket ban on U.S. beef in 2003 after discovering the brain-wasting disease in some specimens.

Japan partially resumed imports in 2005 but reinstated the ban for half a year in 2006.

Since then, Japan has gradually eased import restrictions on the grounds that the United States has been internationally recognized as having the lowest level of risk of the disease.

In May, the government lifted all age restrictions on imported U.S. beef, on condition that parts where prions concentrate be removed before shipment. Such parts include portions of the small intestine and spinal cord of cattle over 30 months old.

At the request of the health ministry, a research panel of the food safety commission began investigating in April last year whether beef from the United States, Canada and Ireland posed a health risk.

In January, it reported to health minister Takumi Nemoto that the risk was “negligible,” leading to the lifting of restrictions this past May.

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