EFSA opinion on the likelihood of BSE infectivity in specified risk material from cattle at different age groups

EFSA has today published an opinion on the likelihood of BSE infectivity in specified risk materials (SRM)[1] from cattle at different age groups. SRMs are the tissues in cattle containing the highest risk of BSE infectivity. These are removed as a key element of the EU BSE controls[2]. EFSA was asked by the European Commission to follow-up on one of its recommendations from its previous opinion (EFSA, 2005[3]) on SRM removal by further estimating the likelihood of the infectivity in SRMs derived from BSE-infected cattle. Following evaluation of new experimental data, the EFSA Panel on biological hazards (BIOHAZ) confirmed that its earlier opinion of 2005 is still valid, which said that BSE infectivity in the central nervous system of cattle occurs during the last quarter of the incubation period in the animal before the disease becomes clinically detectable.

Experimental data confirmed that the “marker” for BSE (the disease-associated prion protein) in the central nervous system of cattle becomes detectable during the last quarter of the BSE incubation period in the animal, before the disease becomes clinically manifest. In applying this prediction model on the likely natural exposure of cattle (rather than artificial laboratory experiments), the BSE “marker” would either not be detectable or would still be absent in the vertebral column in cattle up to and including the age of 33 months.  However, the interpretation of such experimental data needs to take into account the exceptional detection of BSE infection in animals younger than 33 months in EU cohorts born after 2000, and the fact that failure to detect the BSE “marker” does not guarantee absence of infectivity in a tissue[4].

The Panel also noted that the BSE epidemic is in decline[5], and is likely to continue to decrease further, in the different EU Member States. However, the Panel also recommended that there is good reason to consider the risk level of each Member State separately or consider groups with similar characteristics because of differences at the start of various control measures and surveillance between EU member states, as well as differences in the country specific level of exposure.

It is for the European Commission and risk managers in Member States to decide whether any modifications to current controls are warranted, informed by EFSA’s opinion.

[1] Specified Risk Materials are animal tissues in cattle, such as the spinal cord, brain, vertebral column (that includes nervous ganglia), and tonsils which are most likely to carry the infective BSE agent.
[2] Various SRM materials are removed either at all ages (eg tonsils); over 12 months (eg the skull and spinal cord); or at 24 months (eg vertebral column) in cattle in the EU. The 24 month vertebral column risk management decision was made by the European Commission informed by the 2005 EFSA opinion on SRMs
[3] Opinion of the Scientific Panel on biological hazards (BIOHAZ) on the assessment of the age limit in cattle for the removal of certain Specified Risk Materials (SRM)
[4] In updating its previous opinion, the BIOHAZ Panel became aware that scientific consensus on the preferred approach to calculating BSE infectivity recommended by experts in 2005, could not be achieved. This approach, drawing on surveillance data from Member States, would have developed a predictive model of the number of BSE cases in different age groups. The possibility that this approach might not be viable had been anticipated in 2005 as a potential limitation. Hence, the Panel based its opinion on new experimental studies and additional experimental data on BSE detection in cattle together with actual epidemiological data from surveillance rather than any predictive modelling.
[5] Since the implementation of the TSE Regulation in 2001, more than 50 million of adult bovine animals have been tested across the EU and around 7.000 cases have been detected. A constant decline (about 35 % per year) in the number of cases has been recorded: from 2.167 cases in 2001 to around 520 cases in 2005. Only 22 cases concerned animals born after introduction of the total feed ban.

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