Scientific Documents

Opinion of the Scientific Panel on biological hazards (BIOHAZ) on a surveillance programme for Chronic Wasting Disease in the European Union

Summary (96 KB)

Opinion (171 KB)

Annex (356 KB)

Summary

The European Commission (EC) requested the European Food Safety Authority (EFSA) and its Scientific Panel on Biological Hazards for an opinion on a surveillance program for Chronic Wasting Disease (CWD) in the European Union (EU).

The European population of cervids consists of several million free-living cervids and hundreds of thousands of captive cervids. It is theoretically possible for European cervids to be infected by PrPCWD, PrPBSE, PrPScrapie or even an unknown TSE strain; however, it is unknown how the phenotype of such a TSE in European cervids would look like. Currently, only a few European countries conduct surveillance programs on TSE in free-living or captive cervids and only a few experimental research studies are conducted to obtain data on the susceptibility of European cervids for TSE.

During the assessment, opportunities and difficulties were discussed and several problems when considering surveillance for CWD in European cervids emerged influencing the implementation of such a surveillance program. These include the existence of various species and sub-species of cervids, and variation in the cervid population distribution and density in the different EU countries. Different diagnostic methods and currently used tests for TSEs in EU and North America were evaluated and discussed. Sensibility and specificity of the test as presented was evaluated as well as their potential for discriminating different TSEs (CWD – BSE – scrapie) if they occur in cervids.

Evaluation of data submitted for six tests suggest that these rapid tests would appear able to detect a case of TSE in European cervids in a properly defined surveillance program. However, since these tests have not been validated for European cervids it is not possible to recommend specific test(s). In addition, Immunohistochemistry (IHC) and Western blotting tests should be used to confirm a diagnosis of CWD. As there might be differences in sensitivity and specificity between brain and lymph node samples and differences in deposition of PrP as observed in different species of cervids infected with CWD, both retropharyngeal lymph node and the obex of the brain (with intact dorsal motor nuclei of the vagus) should be included in the testing.

At present, biological strain typing by transmission to laboratory rodents is the only definite method allowing differentiation between CWD and BSE/scrapie. Current molecular and IHC methods show potential to differentiate these diseases.

It is recommended to initiate as soon as possible an EU-wide experimental screening on TSE using a rapid test and confirmatory methods and targeting at-risk groups of animals, i.e. farmed deer and fallen stock cervid species in Europe older than 18 months. Experimental studies are essential to understand the pathogenesis, tissue distribution of PrP and to ascertain tissue infectivity of TSEs in European cervids before large scale surveillance could be expected to give reliable results. Such experimental studies should start in parallel with any planned surveillance.

It is also recommended to further support and/or initiate research on molecular methods to differentiate between CWD and BSE/scrapie. Even though human TSE-exposure risk through consumption of game from European cervids can be assumed to be minor, if at all existing, no final conclusion can be drawn due to the overall lack of scientific data. The Working Group thus recognises a potential risk to consumers if a TSE would be present in European cervids. It might be prudent considering appropriate measures to reduce such a risk, e.g. excluding tissues such as central nervous system (CNS) and lymphoid tissues from the human food chain, which would greatly reduce any potential risk for consumers. However, it is stressed that currently, no data regarding a risk of TSE infections from cervid products for humans are available.