Bovine Spongiform Encephalopathy (BSE), was first recognised as a separate disease entity in the UK in 1986. The disease agent, a prion, is believed to be a scrapie-like agent (an infectious protein) that causes destruction of the grey matter in brain, leading to a progressive disease.
- Causes of BSE >
- Effects of BSE >
- Diagnosis of BSE >
- Treatment & Control of BSE >
- Medication/Vaccination for BSE >
Causes of BSE
The infectious agent in BSE is believed to be a specific type of misfolded protein called a prion. Those prion proteins carry the disease between individuals and cause deterioration of the brain. BSE is a type of transmissible spongiform encephalopathy (TSE). TSEs can arise in animals that carry an allele which causes previously normal protein molecules to contort by themselves from an alpha helical arrangement to a beta pleated sheet, which is the disease-causing shape for the particular protein.
The crucial event in the pathogenesis of prion diseases is the
conversion of the normally occurring cellular prion protein (PrPc) into a pathogenic form, called protease-resistant PrP (PrPres) or scrapie PrP (PrPsc).
Effects of BSE
Loss of the animal
Diagnosis of BSE
The clinical signs of BSE are highly varied and diagnosis may not always be straightforward. Most cattle with BSE show a gradual development of symptoms over a period of several weeks or even months, although some can deteriorate very rapidly. Only a small proportion of affected cattle show what would be considered typical "mad cow" signs.
Most suspects show several (but not all) of the following if they are observed closely enough:
- apprehensiveness
- nervousness
- reluctance to cross concrete, turn corners, enter yards, go through doorways or permit milking
- occasional aggression directed at other cattle or humans
- manic kicking when milked
- head shyness, with head held low
- over-reaction to external stimuli
- high stepping gait, particularly hind legs
- difficulties in rising
- skin tremors
- loss of condition, weight or milk yield
- bradycardia
The disease has a long incubation period, from 2 to 8 years, and is mostly seen in adult cattle (youngest diagnosed animal 20 months). Stress appears to induce the symptoms in cattle, and many cases are diagnosed around calving and after transport.
Treatment & Control of BSE
Although the theory of BSE originating from contaminated meat and bone meal is the most widely accepted, other theories about the origin of BSE have been developed. These include suggesting that factors including organophosphorous dipping and an excess of manganese rendered some animals more susceptible to infection than others or that autoimmune disease may be responsible.
The UK has been the main geographical focus of the disease epidemic, although in recent years, other countries, mainly in Europe have experienced BSE cases, particularly Ireland, France and Portugal. BSE has been confirmed in Japan, Canada, and, in 2005, a single case in the USA.
BSE is a notifiable disease and any suspicion of the disease on the farm should be reported to the nearest State Veterinary Services office immediately. Confirmed infected animals are slaughtered and destroyed (incinerated).
The control of BSE in most countries is based on statutory control measures that are mainly aimed at preventing further spread of infectious materials in the feed chain. The following measures are implemented in general:
- Ban on feeding ruminants with all forms of mammalian protein (with specific exceptions, such as calf milk-replacer).
- Ban on all other processed animal proteins, including fishmeal to ruminants.
- Ban on the use of mammalian meat and bone meal in the feed of any food animal species including fish and horses.
- Rendering processes recognised as ineffective in inactivating BSE agent are banned.
- Restricted animal protein use only allowed in non-ruminant species.
Medication/Vaccination for BSE
There is no treatment for BSE. Suspected cases should be reported to the State Veterinary Services immediately.
This info was adapted from Defra’s Compendium of Animal Health & Welfare in Organic Farming, which is a collaborative effort led by Duchy College, Cornwall with VEERU at The University of Reading and The Faculty of Veterinary Medicine, University of Glasgow.
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