Bovine Spongiform Encephalopathy

BSE - 'Mad Cow' disease

BSE is one of a number of Transmissable Spongiform Encephalopathies (TSEs) that affect a range of different animal species including humans. They are called spongiform because as they cause death of scattered brain cells small voids are left. An infected brain looks spongy under the microscope. TSEs are associated with the appearance of 'prions', particles of deformed protein in the central nervous system of infected individuals. It has been assumed that the prions are in some way the infective agent but if so the action of these prions is unclear.

nvCJD

Humans too may suffer from several TSEs. There has been considerable speculation that one: New Variant Creutzfeldt-Jakob Disease (nvCJD), is contracted by eating infected bovine central nervous tissue and extensive precautions have been taken to keep this tissue out of the human food chain.

Despite dire predictions of a devastating wave of human disease very few humans have contracted nvCJD and the rate of infection is dropping. It has only once exceeded 20 cases per year. Around 4 million cases of BSE occurred in the UK peaking in 1992 but there have only been 154 (February 2006) confirmed deaths from nvCJD peaking in 2000.

So far the only humans to die from nvCJD have all shared a combination of genes that occurs in roughly a third of the population.

Cause

It is generally agreed that the origin of the BSE outbreak at the end of the 20th century in Britain was triggered by a change in the regulations governing the feeding of animal products to ruminants. Feed millers were permitted to reduce disinfection procedures but were not required to tell farmers the ingredients in their product.

A great number of theories have been suggested to explain the source of BSE. One early one; that it was a cross infection from scrapie infected sheep, is unsupported by the serum antibody evidence. The prions for scrapie, BSE and CJD are distinct. A suggestion that exotic TSE's from zoo animals might be implicated in BSE has never been fully explored.

Animals injected with extracts from BSE infected central nervous tissue develop neurological disease which might demonstrate transmission of the disease but might instead be the allergic encephalomyelitis described by Pasteur.

Auto-Immune

Another possibility is that BSE (and some other TSVs) is an auto-immune disease triggered by the presence of Acinetobacter — common bacteria that contain protein structures remarkably similar to those found in brain tissue. Antibodies produced in response to this protein would also be antibodies to the sufferer's own nervous tissue.

In short

Despite considerable research the source of BSE remains a mystery.
BSE in UK cattle is approaching extinction due to strict control measures.
If nvCJD is linked to BSE it is rarely transmitted.
nvCJD rates never reached the millions predicted by media pundits. There were 5 cases confirmed in 2005

BSE as an auto-immune disease
Spongiform Encephalopathies
National Creutzfeld-Jakob Disease Surveillance Unit
Current CJD figures