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New Protocol for Atypical BSE Investigations

28 July 2014

The European Food Safety Authority, EFSA, has developed a laboratory protocol on how to conduct new studies for investigating the presence of the agent of Atypical Bovine Spongiform Encephalopathy (BSE) in tissues of infected cattle.

Guidance includes the number of animals to be tested, the tissues to be analysed and the methods to detect the agent of disease.

BSE belongs to a group of diseases called Transmissible Spongiform Encephalopathies that affect the brain and nervous system of humans and animals. BSE can be divided into Classical BSE and Atypical BSE.

Current knowledge on Atypical BSE is limited and the implementation of the protocol is designed to contribute to fill information gaps.

Following a request from the European Commission, EFSA was asked to provide scientific and technical assistance on a protocol for further laboratory investigations into the distribution of infectivity of Atypical Bovine Spongiform Encephalopathy (BSE).

The European Union Reference Laboratory (EURL) for Transmissible Spongifom Encephalopathies (TSEs) conducted experiments (referred to as the EURL study) that resulted in the collection and storage of reference material originating from cattle experimentally infected with Atypical BSE (H-BSE and L-BSE).

With the intention to generate relevant data that could inform further policy options regarding BSE, in particular as regards rules on specified risk material (SRM), DG SANCO wished to explore the possibility to submit these tissue samples to further investigations.

EFSA was asked to propose a laboratory protocol to perform new studies aimed at investigating the presence, distribution and relative level of infectivity of Atypical BSE (H-BSE and L-BSE). EFSA was also expected to reflect on whether the tissues available from the EURL study are sufficient for the purpose and/or suggest that investigations on other tissues might be possibly needed.

Data relating to the prevalence and geographical distribution of Atypical BSE in the European Union (EU) are incomplete and subject to variation owing to the ongoing retrospective typing of BSE cases.

So far, 80 cases of Atypical BSE have been reported by EU Member States from 2001 to 2014.

All Atypical BSE cases have been detected by active surveillance, typically in animals over eight years of age, with a similar number of cases detected each year.

The EFSA report provides an overview of the biological material collected from field cases of Atypical BSE and transmission studies, both in the framework of the EURL study and additional published scientific studies.

It was concluded that information on the pathogenesis and tissue distribution of Atypical BSE in cattle through the study of field cases and experimental transmission studies is lacking.

The latter are limited to transmission of Atypical BSE through intracerebral (i.c.) inoculation of cattle. Where data exist from both field cases and experimental animals (i.e. for L-BSE only), there is good agreement of the data with regard to abnormal PrP distribution.

There are no data for field case H-BSE. All data currently available relate to the presence or absence of PrPSc, but do not quantify relative amounts of PrPSc or levels of infectivity.

Approaches to quantify Atypical BSE prions in cattle tissues are described and reviewed, including bioassay and in vitro methods.

A laboratory protocol for further studies is recommended.

Its application would provide elements allowing the assessment of the relative infectious titre, PrPSc accumulation and prion seeding activity in the tissues of cattle that developed H-BSE or L-BSE (using posterior brainstem as a reference).

Tissues to be covered by those studies were categorised in three priorities, based on their inclusion in the cattle SRM list, on the presence of infectivity, or PrPSc presence, demonstrated in Atypical BSEs or other TSEs in ruminants, and on the importance in terms of input into the food chain in the EU.

The protocol provides details in terms of the minimum number of animals to be tested, processing and preparation of tissues, and methods to be used to identify abnormal PrP and quantify infectivity, also depending on the expected level of infectivity and amount of tissue available for analysis.

Applying the protocol only to the tissues obtained through the EURL study would provide information on some but not all the tissues from the cattle SRM list. It would also provide information on some additional tissues not included in the cattle SRM list, but relevant for the food chain.

Material from other studies could be used to augment the range of SRM and non-SRM tissues available.

It is acknowledged that there is no identified source able to provide all the samples necessary to assess infectivity in tissues belonging to the full cattle SRM list in H- and L-BSE-infected animals, and therefore, to complete this objective, new inoculation experiments with H- and L-BSE agents in cattle would have to be considered. Recommendations on general principles for such new experiments are provided.

In accordance with former EFSA recommendations, it is recommended that, through the implementation of the protocol, information should also be obtained on the performance of currently validated rapid tests for TSE active surveillance in cattle/bioassay for detecting H-BSE and L-BSE agents.

July 2014

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