EFSA reviews BSE/TSE infectivity in small ruminant tissues

EFSA has published today a scientific opinion on Transmissible Spongiform Encephalopathy (TSE)[1] infectivity in the tissues of small ruminants such as goats and sheep[2]. Based on new scientific evidence and taking into account the current situation with respect to the occurrence of TSEs in animals in the EU, EFSA’s Biological Hazards (BIOHAZ) panel has reviewed the distribution of TSE infectivity in small ruminant tissues and has provided for the first time a quantification of the impact of current SRM measures in managing TSE-related risks in small ruminants. The removal of Specified Risk Materials (SRM)[3] such as the brain and spinal cord from animals going into the food chain protects consumers from TSE-related risks. EFSA’s advice will help inform risk managers in the implementation of measures outlined in the TSE Road Map 2[4].

In this opinion, EFSA’s Biological Hazards (BIOHAZ) Panel reviews the latest scientific data on the infectivity of different small ruminant tissues for Classical scrapie, Atypical scrapie and BSE and takes into consideration aspects such as the age and genetic makeup of the animals. With the exception of Bovine Spongiform Encephalopathy (BSE), other TSEs in animals such as scrapie have not been found to be transmissible to humans.

The Panel noted that only one single case[5] of naturally occurring BSE has ever been identified in small ruminants worldwide. Moreover, the opinion provides a set of simulations quantifying for the first time the impact of different SRM options on reducing the risk from the possible presence of BSE in small ruminants. The Panel says that, should a BSE-infected small ruminant ever enter the food chain[6], the current SRM policy would allow a 10-fold reduction of the infectivity load, that is the level of TSE agent present in an infected animal. Experts also advise that the use of the dressed carcass only (excluding the head and the spinal cord) would allow a greater reduction of the BSE exposure risk than the current SRM measures.

With respect to classical scrapie, the panel concludes that, as for BSE, the current SRM policy allows a 10-fold reduction of the infectivity load. The Panel points out that a modification of the SRM list based only on considerations for BSE will also have an impact on human exposure to Classical and Atypical scrapie agents. In addition, the Panel adds that the infectivity of goat kids below 3 months of age is negligible, even if they come from infected herds.

For Atypical scrapie in sheep and goats, the Panel says that since some infectivity, albeit at low levels, can be found in other tissues[7] than those specified in the SRM list, it cannot be assumed that the current SRM measures will prevent the entry of the Atypical scrapie agent into the food chain.

The Panel recommends further improving data collection and risk assessment in this area of work. In particular, it recommends updating this opinion when data from ongoing experiments, such as those concerning the development of BSE in goats, become available. The Panel specifies that the development of specific assessment models could provide a more precise estimate of the impact of SRM removal policies on managing risks from TSEs.

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[1] Transmissible Spongiform Encephalopathies (TSEs) are a family of diseases that affect the brain and nervous system of humans and animals. The diseases are characterised by a degeneration of brain tissue giving it a sponge-like appearance. TSEs include Bovine Spongiform Encephalopathy (BSE) principally found in cattle, scrapie in sheep and goats, as well as variant Creutzfeldt Jakob Disease (vCJD) and other diseases in humans. Whilst scrapie (classical and atypical) has been known for centuries as a disease affecting sheep and goats , to date only one single case of naturally occurring BSE has ever been identified in small ruminants. More information on TSEs
[2] This opinion updates a previous opinion on TSE Infectivity distribution in ruminant tissues issued by the Scientific Steering Committee (SSC) of the European Commission of 2002.
[3] Specified risk materials are the tissues containing the highest risk of BSE infectivity. In the EU the removal of SRM, which is the most important public health measure to protect consumers from BSE risk, is mandatory since 2000. Various tissues including the brain, spinal cord, vertebral column, tonsils and ileum are classified and then consequently removed as SRM with specific rules defined by animal species and according to age. The list of SRM is indicated in Annex 5 of Regulation EC 999/2001
[4] The road map is a strategic document of the European Commission which outlines possible future changes to measures in place in the EU to manage the risk of BSE and other TSEs and ensure a high level of consumer protection. On 16 July 2010 the Commission adopted a Communication to the European Parliament and the Council outlining areas where future possible changes to EU TSE-related measures could be made. The TSE Road Map 2 – A strategy paper on Transmissible Spongiform Encephalopathies for 2010-2015
[5] One goat slaughtered in 2002.
[6] In the EU, sheep and goats found to be infected with TSEs are excluded from the food and feed chain.
[7] Atypical scrapie infectivity can be found for instance in lymphoid tissues, nerves and skeletal muscles.