The first cases of Bovine Spongiform Encephalopathy (BSE) were seen at the end of 1984. At the time, vets had no idea this was a new neurological disease in cattle.

It was another two years before the first paper was published on the symptoms and pathology of what became known as Mad Cow Disease.

At the height of the epidemic in the winter of 1992/93, more than 3,500 cases of BSE were recorded each month. To date, approximately 170,000 cases have been confirmed and another 100,000 cattle have been culled in an attempt to stop the spread of the disease.

BSE very nearly destroyed the British beef industry. Especially when a link was made to a human form of the disease, Creutzfeldt -Jakob Disease (CJD). The UK Government announced in 1996 that a new strain of CJD had emerged - most probably as a result of eating infected meat - and virtually overnight, people stopped buying beef.

Contaminated feed

BSE was dubbed Mad Cow Disease by the popular press, after pictures were shown of disoriented, brain-damaged cattle collapsing in their pens.

When the heads of the animals were sent for post-mortem, fluid-filled cavities - vacuoles - could be seen in the brain cells, giving them a spongy appearance.

Scientists thought that scrapie had been passed on from sheep to cattle

The theory was proposed that scrapie - a similar disease in sheep - had passed to cattle. The finger of blame was pointed at the special feed given to young dairy cows. This was a concentrate containing the ground-up remains of slaughtered animals - including sheep. The feed was a rich source of protein, but it also contaminated with the infective agent that caused scrapie.

Opponents of the theory doubted whether scrapie could actually jump to another species. After all, the sheep disease had been around for at least 200 years and animal products had been included in cattle feed for several decades. If the theory was correct, BSE should have emerged much earlier.

Abattoir procedures

However, crucial changes had been made to the regulations governing the way animals were slaughtered in abattoirs. Previously, the waste animal material used in feeds had been heat-treated to remove water and fat. A solvent was then applied to the material to dissolve any residual fat. Finally, the remains were cleaned with steam.

Farmers were hit hard by widespread cattle fatalities

The new regulations permitted abattoirs to drop the use of solvents. It seems the simpler process was less effective at deactivating the scrapie agent. This was confirmed by epidemiological studies that showed cattle fed concentrates prepared under the old process remained relatively BSE free.

The UK Government introduced a series of measures to contain the epidemic. The most important were the ban on the use of ruminant protein in ruminant feed (July 1988) and the payment of 100% compensation for the slaughter of animals suspected of having BSE (February 1990). Currently less than 50 cases of BSE are reported each month.