On Wednesday, March 20, 1996, "Mad Cow Disease" grabbed headlines worldwide. The shock waves were generated by a group of prestigious British scientists who revealed that the fatal cattle disease was likely being transmitted to humans.1 The news brought the British meat industry to a virtual standstill. English folk avoided the meat markets. The European Union and a cascade of other countries banned British beef. When the dust had settled, beef imports had been banned by 23 nations.
Since 1986, autopsies of British cattle dying with mad cow disease revealed a nervous system infection that ate tiny holes in the brain. When viewed under a microscope, the brain actually looked like a sponge. This sponge-like appearance gave rise to the disease's scientific name: Bovine Spongiform Encephalopathy or "BSE." This cumbersome name could literally be translated: cows' (bovine) sponge-like (spongiform) brain disease (encephalopathy).
The lay term, "mad cow disease," in addition to being much easier to pronounce and remember, also conveys the fact that infected cows often develop mental deterioration and behavioral abnormalities. "Formerly" docile animals become irritable, nervous, or aggressive. They often lose weight, and develop severe coordination problems before dying within two weeks to six months.2 The number of cattle affected is staggering, as stated in Figure 1: Cases of Mad Cow Disease.3
Beside being a terrible tragedy for the cattle population, BSE has powerful emotional appeal for other reasons. It is one of a group of fatal brain diseases that can be transmitted from one living creature to another. These diseases are technically called "transmissible spongiform encephalopathies." Many British consumers had apparently comforted themselves for years with the thought that it was unlikely for BSE to spread from cows to humans. However, even before March, 1996, there were serious concerns about human risk, because transmissible encephalopathies were known to affect many other animals besides cattle. Mice, sheep, goats, monkeys, pigs, mink, and other cattle have all come down with a spongiform encephalopathy when given meat from cattle that were known to have the disease. Roughly 20 animal species have been documented to come down with diseases resembling BSE. They are listed in Figure 2: Animals Afflicted with Diseases Resembling BSE.4
Furthermore, cattle themselves likely contracted the disease from a different species. The epidemic in British cows has been traced to a similar sheep spongiform encephalopathy called scrapie.5 This sheep disease gets its name from the fact that afflicted sheep can become mentally deranged and are known to literally scrape the wool off their own hide.
Before concerns about mad cow disease surfaced, it was common for British cattle to receive protein supplements in the form of meat and bone meal from other animals such as sheep.6 Evidence suggests that the practice of feeding these reprocessed sheep carcasses (which included their brains) to cattle allowed the cow population to acquire BSE. Before the full extent of the problem was recognized, disease transmission was further amplified when the carcasses of BSE-infected cows were also used in the process of making animal feed.7, 8 Thus, healthy cows were not only fed infected tissues of sheep but also of other cows.
