Eradication and Control of BSE by Vaccine

Control and eradication of BSE

On the assumption that asymptomatic cattle under 30 months would not be able to pass on infection, MAFF agreed early in 1996 to slaughter, as a safety measure, either beef or dairy breeds over 30 months old. On average over 800,000 cattle were killed each year, turned into MBM and burnt. Since symptoms were unknown in younger cattle that this safety measure would be an effective strategy to break the chain of infection appears to be wishful thinking.

Killing 800,000 cattle, year after year, and turning them into 400,000 tons of MBM to be burnt is a very costly affair. Why not think of a long-term permanent solution? To solve this problem the surplus animals should be culled at a much earlier age. At the beginning, it may not reduce the number of animals slaughtered. However, it will reduce the weight of the dead carcasses to be handled, making a big difference to the amount of MBM and compensation paid. It should be pointed out that because of vertical transmission, culling cattle at any age is not sufficient to eradicate BSE. Only animals, which have been tested, should be used for breeding. Such a test is available.

Vaccine

The possibility of developing a vaccine against BSE is suggested by the existence of a phenomenon analogous to "interference". This possibility should be fully explored.

There are some 20 different strains of the scrapie agents. Infection with one strain blocks the others. Thus there must be some immune mechanism involved, which we have not been able to demonstrate.

Experimental feeding of cattle, cats and mink with Type 1 scrapie sheep brain tissues has revealed that these animals do not develop a clinical disease even after eating large quantities of contaminated brain tissue. This is a very important observation On the other hand, mink and calves fed or injected with BSE always develop the disease. It would be of great importance to know if this scrapie strain of the agent blocks the BSE agent when mink and cattle prechallenged with scrapie are then challenged with BSE.

Development of such a vaccine would stop horizontal transmission of BSE in cattle and help to eradicate the disease and protect against environmental infection of cattle. If this phenomenon is true for humans, many of us will have eaten scrapie-infected tissues and will therefore be naturally protected from BSE, which would be a great comfort to know.

Prusiner’s colleague Mike Scott now also believes that the scrapie strain is somewhat dominant, preventing the BSE strain from infecting cattle and people when both are present. In other words the scrapie strain acts as a vaccine against the BSE strain.

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