Links between TSEs in animals, humans reviewed

by Bryan Salvage
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PARMA, Italy – A joint opinion reviewing the latest available scientific information on possible links between Transmissible Spongiform Encephalopathies in animals and humans has been published by the European Food Safety Authority and the European Centre for Disease Prevention and Control. Current epidemiological and laboratory tools and methods for the evaluation of possible association of animal and human TSEs were also critically evaluated.

Findings confirm that at present, the only TSE proven to be zoonotic (i.e. transmissible from animals to humans), remains Classical Bovine Spongiform Encephalopathy, known in humans as variant Creutzfeldt-Jakob disease. Epidemiological evidence shows the most common form of TSE in humans is sporadic Creutzfeldt-Jakob disease.

What causes sporadic CJD remains uncertain. Although scientific research to date has not identified an environmental source of infection, the panel could not exclude the possibility that a small number of cases could be zoonotic.

EFSA and ECDC have made the first comprehensive review of epidemiological and laboratory studies on possible links between TSEs in animals and humans at EU level. The opinion builds on previous work carried out by EFSA on the zoonotic potential of single TSE agents, as well as a considerable number of other scientific studies on prion diseases.

No epidemiological evidence suggests Classical scrapie in goats and sheep is zoonotic. Regarding Atypical scrapie in sheep and goats, the scientific data currently available are too limited to conclude whether it has the potential to be zoonotic or not.

For other TSEs, a number of uncertainties make it impossible at present to draw definite conclusions on possible links between animals and humans. One reason for this is data on the monitoring of TSEs in animals are too recent to be compared to the respective human data. The opinion therefore recommends that systematic monitoring of TSE diseases be continued in both humans and animals.

Scientists also evaluated evidence obtained from experimental transmission of TSEs in laboratory studies. The opinion states the results of some of these studies suggest there might be a possibility of animal-to-human transfer for other TSEs, in addition to Classical BSE in cattle. Some data indicate one of the new atypical BSE agents, the L-BSE or BSE agent, may have a similar or higher zoonotic potential than the Classical BSE agent. The opinion, however, points out that at present it is not possible to define how informative these laboratory studies are for measuring the transfer of TSEs between animals and humans under real exposure conditions.
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