“Transmissible Spongiform Encephalopathy” is the name given to a group of diseases that cause the brain to deteriorate and to develop holes, giving the brain a sponge-like appearance. The diseases are considered “transmissible” because they can spread from one animal to another, either through ingestion of an infected animal or by injection. All mammals tested so far can develop TSEs. TSEs are found in many mammals including humans, cows, sheep, cats, hamsters, mice, goats, deer, mink and some zoo animals. It has even been shown that pigs can develop these diseases through inoculation.

     Because these diseases cause the deterioration of the brain and affect the nervous system, animals infected with TSEs suffer from physical and psychological problems like loss of coordination and dementia, and eventually die. Tissue samples from the brains of animals that die from a TSE have holes throughout, resembling a sponge (see Fig.1). This is where the disease gets the name “spongiform”.

     BSE or mad cow disease, as it is more commonly called, is probably the most well-known TSE. In 1986 the first case of BSE was found in the United Kingdom (UK). The disease begins with a two- to five-year incubation period after the cow is infected when there are no obvious symptoms. After that it becomes anxious or agitated. As the disease progresses the animal starts having small muscle spasms and losing weight. It loses control and they get into frenzied movements like head butting walls. The animal will die a short time after this.

     A cow may be infected with BSE through either injection or by eating feed that contains the body parts of an animal infected with a TSE. It is thought that over the period of 1978-1980 when the manufacturing process of feed for cattle changed, that the feed became contaminated with infected body parts, resulting in the transmission of a TSE to cattle. By 1994 there were 850 cases of BSE reported every week in the UK.

     Humans can develop a TSE disease called Creutzfeldt-Jakob Disease (CJD). The characteristics of this disease include initially disturbed sleep and eating habits. It then progresses to muscular spasms and dementia. One year after the first appearance of symptoms, 90% of people with CJD die, another 5% in the second year and the remaining 5% take up to 10 years. In the past the disease was usually transferred through medical processes or rarely inherited, however there is now a new disease called New Variant Creutzfeldt-Jakob Disease (nvCJD). As in the case of BSE, with nvCJD there is an initial period of incubation during which there are no symptoms.

     At first it was believed that humans could not get BSE disease from infected cattle. Humans continued eating beef thinking they were safe. However, several new cases of a nvCJD were found in the UK. When it was discovered that the cause of this disease was meat from cattle with BSE, the UK started taking action. In 1988, the UK stopped the practice of adding cow body parts to cattle feed. In 1989 the British government banned human consumption of bovine tissue, lymphoid tissue, spleen, gut, and thymus.

     Scientists now know that there are TSEs that affect sheep, goats, monkeys, mice, hamsters, and pigs. It is thought that all mammals can contract TSEs, either orally or by inoculation. The TSE that affects sheep is called Scrapie. Animals with this disease are very irritable and get an unbearable itch. This causes them to rub up against objects and rip off their wool. They also have impaired vision and lose weight.