EFSA publishes quantitative risk assessment on the residual BSE risk in sheep

EFSA has been asked by the European Commission for an update on the risks posed by sheep tissues to human health if BSE was present in sheep. BSE has not been found to naturally occur in sheep. However, it has proved possible in experimental conditions to infect sheep with BSE. Consequently, there is a theoretical possibility that sheep could contract BSE.

In the EU, testing of TSE positive sheep for BSE is done by tests that can discriminate between BSE and scrapie (a sheep TSE considered of no risk to human health). This testing has increased since the finding of a BSE positive goat in France in 2005. From 2002 on, more than 1.5 million sheep were tested for TSE and all of the positive cases which were then tested with a discriminatory test yielded negative results for BSE.

However, negative test results cannot statistically rule out the possibility of BSE being present in the sheep population. Considering the worst case scenario that BSE could be present in countries with a substantial BSE history, statistical modelling indicates that the number of cases would be less than 1 per 20,000 animals at slaughter.

EFSA’s BIOHAZ Panel confirmed existing views that if BSE would naturally occur in sheep, the effectiveness of the current Specified Risk Material (brain, spinal cord and spleen) removal measures would be limited in protecting consumers against BSE, as experiments have shown that BSE agents can spread throughout all animal tissues. They also confirmed the assumptions of past opinions that there is no intrinsic species barrier for sheep BSE transmission to humans. That means that the health risks from sheep affected with BSE, were BSE found to naturally occur in sheep, could also apply to humans.

[1] TSE = Transmissible Spongiform Encephalopathy: A family of transmissible progressive diseases that mainly affects the central nervous system, characterized by spongiform degeneration and a long incubation period. Examples of TSEs are Creutzfeldt-Jakob Disease (CJD) and kuru in humans, scrapie in small ruminants and Bovine Spongiform Encephalopathy (BSE) in bovines.
[2] Panel on Biological Hazards