By studying prions, researchers from Toulouse in France have identified the origin of bovine spongiform encephalopathy, better known as the “mad cow disease”. They then warned of the possible return of the disease.
Cattle
Bovine spongiform encephalopathy (BSE), is a degenerative infection of the central nervous system of cattle. The disease appeared in the 1980s in the United Kingdom before spreading to Europe and North America in the 1990s. Today, researchers in Toulouse have found the possible origin of this disease and warn of its possible reappearance. The results of this study were published on Monday 16 December in the journal Nature Communications.
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For their work, the researchers from INRA (Institut National de la Recherche Agronomique) and ENVT (Ecole Nationale Vétérinaire de Toulouse) worked with prions. These are proteins that can become pathogenic by adopting an abnormal form, which is different in each species. More specifically, they used the prion that causes scrapie in sheep and injected it into rats genetically modified to make the bovine prion.
Result of the experiment: in 95% of the cases, the rodents developed a bovine spongiform encephalopathy. These genetically modified mice are “a very good model, which works well for finding out what would happen if cows were exposed to these prions,” explains Olivier Andreoletti, an INRA researcher who led the study.
Today, the food chain is protected
For the first time, these data provide an experimental explanation for the emergence of mad cow disease in the mid-1980s in the United Kingdom, INRA says in a press release. BSE was then transmitted among cattle throughout Europe, North America and many other countries, probably through a diet rich in meat and bone meals and offal from diseased animals.
By consuming products from infected cattle, several people developed a variant of Creutzfeldt-Jakob disease. Europe began to ban meat-and-bone meal, monitor for possible cross-contamination and destroy the highest risk tissues, which significantly slowed down the outbreak.
“Today the food chain is protected by these measures and as a result, there are no more cases of contamination and we have almost eliminated BSE,” explains Olivier Andreoletti. Only a few cases remain, such as the one detected in the Ardennes in 2016.
The risk of an epidemic has not completely disappeared
However, the risk of an epidemic still exists. “Despite the economic cost of these measures and the virtual disappearance of BSE cases, the risk of a re-emergence of BSE from atypical scrapie cases in small ruminants argues for the maintenance of the most fundamental measures (ban on meat and bone meals, systematic removal, and destruction of the highest risk tissues, etc.) which have made it possible over the last 20 years to protect consumers and production chains from “mad cow disease”,” says the INRA.
“The measures put in place are costly and there is now pressure from the industry. Some are talking about lifting the ban on recycling carcasses into meat and bone meals. We are not here to give lessons, but to produce knowledge,” says Olivier Andreoletti, who fears that the European Commission will accept the return of meat and bone meals to the market. For the researchers, “if we start using the same practices again, we will have the same effects”.
“Prion diseases are neurodegenerative diseases that cause progressive neurological disorders with fatal results after a long and silent incubation period. They affect humans (Creutzfeldt-Jakob disease), farm animals (mad cow disease, scrapie in sheep and goats, dromedary prion disease) and wild animals (chronic deer wasting disease),” INRA explains on its website. The symptoms can be locomotor, sensory and behavioral.
References
- https://www.pnas.org/content/early/2019/12/11/1915737116
- http://www.envt.fr/content/recherche-inra-envt
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