Possible Transmission of BSE and Scrapie to Fish

A new paper* is addressing the transmissibility of BSE and Scrapie to fish.

TAFS comments on the paper:
The authors describe an experimental challenge of fish (Gilthead Sea bream), and acknowledge that they still have to prove that the fish were actually infectious. The paper is mainly descriptive pathology, but appears to be worthy of consideration. Confirmation that the deposits identified in the brains of challenged fish is infectious is however important.

The fish were exposed orally (force-fed), to a total of approx 50mg of BSE-infected (or scrapie infected) brain tissue, divided into five doses, administered at two weekly intervals. While the outcome may demonstrate a theoretical risk of infection in fish, future risk assessments will need to take into account many more factors. While in the UK there was no evidence of susceptibility of fish in 1996, when the feeding of mammalian meat and bone meal (MBM) to fish was first prohibited. The key reason for the prohibition was to prevent the circulation of mammalian MBM, with risk of accidental contamination of ruminant feed. It was not because the fish were thought to have been at risk.

Since then of course fish meal has also been prohibited from ruminant feed (except for limited exclusions) in the EU, but again, this was primarily because it was not possible to exclude the possibility that the fishmeal was contaminated with mammalian MBM. Discriminatory tests are still not sufficiently robust to ensure that contamination does not occur.

Future risk assessments will however need to take this result into account, especially if the fish are shown to be truly infected. It does mean that fish waste that is converted into fish meal could theoretically end up infecting ruminants if recycled. Having said that, it is important to remember that:-
a) the prevalence of BSE in cattle, and protective measures in force, are going to be key factors in determining whether or not there is a real risk of infecting farmed fish, if they are fed on ruminant MBM. In countries where controls are in place, with SRM removed and destroyed, it is most unlikely that fish will be exposed to sufficient infectivity to result in infection. Methods of meal production may also reduce the likelihood of high infectious doses in the meal. In countries where BSE controls, such as SRM removal, are not in place, the likelihood of infectivity being present will be dependent on BSE prevalence. OIE country categorisation gives an indication of this risk, but at present no countries are currently identified as representing a high risk.
b) in most countries where fishmeal is fed to livestock, it largely arises from fish caught at sea, which will not have been fed on ruminant MBM. It is possible however that the development of fish farming to meet long term nutrition needs of consumers could present a danger to cattle if their waste was recycled in large volumes to cattle (but only if they have been fed BSE in the first place). Perhaps more importantly would be the feeding of fish on fishmeal produced from infected farmed fish of the same species. Recycling within a species has the potential to adapt the agent to the species, with the result that they are more easily infected. The UK BSE epidemic was an example of recycling within a species which resulted in the exposure of increasing numbers of cattle with each phase of recycling. It has to be noted however that in many countries the conditions under which animal wastes are processed have changed, and may no longer represent the same potential for recycling that led to the BSE epidemic.
c) key to whether or not infected fish represent a risk to farm animals, fish or humans will be the biological properties of the agent, if it is demonstrated that the fish are actually infected. Will the agent behave like BSE or scrapie? While behaviour that is identical to bovine BSE may be assumed to represent a similar risk to animals or humans that consume infected tissues, any deviation from the BSE characteristics means that the risks cannot be quantified. There is currently no evidence that other prion diseases of animals represent a danger to humans (see TAFS statement on the transmission of scrapie via milk).


*Salta E, Panagiotidis C, Teliousis K, Petrakis S, Eleftheriadis E, et al. (2009) Evaluation of the Possible Transmission of BSE and Scrapie to Gilthead Sea
Bream (Sparus aurata). PLoS ONE 4(7): e6175. doi:10.1371/journal.pone.0006175

Risk Management Paratuberculosis

TAFS published its first position paper on a non-TSE animal disease today. It is a recommended risk management plan for paratuberculosis and available for download from the TAFS website.

Fish study holds hope for CJD drug

We know that rogue prions cause CJD and mad cow disease, but what normally folded prion proteins do has been a mystery, because experimental mice without them are almost normal.

Now Edward Málaga-Trillo and colleagues at the University of Konstanz in Germany have discovered that depriving zebrafish of prions has a much more obvious effect. This holds out hope for future drug development (PLoS Biology, DOI: 10.1371/journal.pbio.1000055).

Zebrafish have two versions of the protein. Blocking one stops the brain forming correctly; blocking the other stops the cell migration that guides embryo growth. Time-lapse photos show that the prions help cells to signal and stick to each other.

The finding may explain why disrupting normal prion production causes the dementia of CJD. "In fish embryos we see the protein helping cells communicate," Málaga-Trillo told New Scientist. "It may do something analogous in the mammalian brain, such as building synapses. That may be what goes wrong in prion diseases."

The work also means zebrafish might be useful in drug development. Because disrupting prions has such dramatic effects in these embryos, a drug that protects the protein should be easy to identify.

Source: New Scientist, 2699, March 11, 2009

2 more position papers on TSE updated

Two more updated versions of TAFS Position Papers on TSE have been posted today:
- Testing of cattle for BSE
- Slaughter practices and the dangers of carcase contamination with BSE.

The papers can be downloaded from the TAFS website.

3 position papers on TSE updated

Three updated versions of TAFS Position Papers on TSE have been posted today:
- BSE in small ruminants
- Transmission of scrapie via milk
- Specified risk materials.

The papers can be downloaded from the TAFS website.

Metro Group represented in TAFS

As per January 1st, 2009, TAFS welcomes Mr. Hans-Jürgen Matern of MGB Metro, Düsseldorf, Germany, as its latest member.

Mr. Matern is Division Manager Quality Assurance at MGB Metro.

Welcome!

New website of OIE reference laboratory for paratuberculosis

If you are interested in paratuberculosis, you will either know already or find it good to know now that the Veterinary Research Institute, Brno, Czech Republic, opened new web pages of the OIE reference laboratory for paratuberculosis.

In particular the weekly updated list of publications on paratuberculosis/Johne's disease will be very useful for the community.

Source: Centaur news flash information