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No Proof of Link Between Scrapie and sCJD

12 August 2015

ANALYSIS - There is no scientific proof that scrapie in sheep can be transmitted from sheep to humans.

This is the main finding of a new scientific opinion from the European Food Safety Authority’s Panel on Biological Hazards (BIOHAZ Panel).

The finding follows an assessment of research published last year Evidence from zoonotic potential of ovine scrapie prions by Cassard and others.

This research through laboratory experiments on mice found that under certain circumstances some Classical scrapie isolates can produce prion proteins that can become similar to those causing one form of sporadic Creutzfeld-Jakob Disease.

Because of this the research said that under certain circumstances scrapie prions have the potential to be zoonotic – can be transmitted to humans.

However, the research did not show that it could or did take place under field conditions.

An earlier scientific opinion in 2011 from EFSA found that some animal Transmissible Spongiform Encephalopathies could be zoonotic but it could find no link between Classical or Atypical scrapie and sporadic Creutzfeld-Jakob Disease.

“Current evidence does not establish this link, and no consistent risk factors have been identified for sCJD,” the latest EFSA scientific opinion says.

It adds: “Based on a limited number of Classical scrapie and sCJD isolates investigated so far by transmission in voles, there is no evidence of any common strain involved in Classical scrapie and sCJD, but the number of isolates studied is far from comprehensive at this point.”

The BIOHAZ Panel indicates that the level of exposure for humans to scrapie is largely determined by the prevalence of the disease in sheep and goats and by the amount of infectivity in the sheep and goat tissues entering the food chain.

These parameters have to be considered when the public health risks associated with exposure of consumers to scrapie agents through sheep and goat products are examined.

The exposure of consumers through the food chain is reduced by the current specific risk material (SRM) measures within slaughterhouses that demand that certain potentially infected tissues are removed before the meat is declared fit for human consumption.

However, the BIOHAZ Panel said that from the available epidemiological evidence, it is not possible to conclude that the exposure of consumers to ovine products has resulted in the transmission of prion diseases to humans.

To be able to assess the risk further it would be necessary to examine the spread of the disease in the sheep and goat populations alongside consumption data and the frequency of incidents of sporadic Creutzfeld-Jakob disease.

Surveillance in Europe has shown that on average deaths from sCJD are about one to one and a half in every million people.

The majority of cases of sCJD are spontaneous with no external source of infection.

The BIOHAZ opinion adds that there is evidence of a mismatch between potential human exposure to scrapie and the mortality rates of sCJD - in Australia and New Zealand, for example, where there is minimal exposure compared to Iceland and Cyprus where there is high exposure.

The opinion says the data argues against the possibility of a link.

“It is concluded that current evidence does not establish a causal link between scrapie and sCJD, and that the possibility of scrapie-related public health risks from the consumption of ovine products cannot be assessed,” the BIOHAZ opinion says.

Further Reading

You can view the full report by clicking here.

Chris Harris

Chris Harris

Top image via Shutterstock



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