Greek scientists have discovered that it is possible for fishes to contract mad cow disease.
Evgenia Salta and coauthors published the results of their studies on the transmissibility of bovine spongiform encephalopathy (BSE or mad cow disease) and scrapie (another transmissible spongiform encephalopathy, TSE) in the gilthead sea bream (Sparus aurata, a species widely farmed for food) in a recent issue of the journal PLoS ONE.
The authors divided 1600 sea bream into groups of 200 and force-fed each group with a variety of infected, and non-infected brain homogenates, ranging from scrapie-infected sheep, healthy control sheep, BSE-infected cow and healthy control cow.
The force-feeding procedure was repeated fortnightly for a total of five treatments.
Following the inoculation period, all fish were kept on a maintenance diet with commercially feed to prevent excessive growth and overcrowding during the multiyear study period.
The authors observed the fishes for any signs of abnormalities in behaviour or in swimming, and regularly examined sacrificed individuals (at 3, 6, 8, 10, 12, 14, 16, 18, 24 months) to examine the histology of organs such as the brain, spleen and intestine.
Finally, the authors confirmed the presence of the appropriate prion proteins (PrP) " the agents responsible for spongiform encephelopathies " using immunohistological methods.
The authors found that while the bream never displayed clinical signs of spongiform encephelopathies during the study period, the brains of TSE-fed fish sampled two years after challenge showed signs of neurodegeneration and accumulation of deposits that reacted positively with antibodies raised against sea bream PrP. The control groups, fed with brains from uninfected animals, showed no such signs.
While the authors acknowledge that more studies are needed to study infectivity and transmission of TSEs in fish, the prospect of farmed fish being contaminated with infectious mammalian PrP, or of a prion disease developing in farmed fish is an alarming one.
They conclude that ...the possibility that the affected sea bream brain tissue might be infectious, must be taken seriously in any consideration to lift EU feed bans, especially those related to farmed fish.
For more information, see the paper: Salta E, C Panagiotidis, K Teliousis, S Petrakis, E Eleftheriadis, F Arapoglou, N Grigoriadis, A Nicolaou, E Kaldrymidou, G Krey and T Sklaviadis (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