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BOVINE SPONGIFORM ENCEPHALOPATHY DEFINITION Bovine spongiform encephalopathy (BSE) is a recently recognised nervous condition of adult cattle. It was first recorded in the South of England in 1985 but has since been identified in all parts of the UK. The disease has an insidious onset with a varied spectrum of behavioural and locomotor disturbances. The clinical signs are progressive and the disease is invariably fatal. In the summer of 1988 BSE was made a notiflable disease. EPIDEMIOLOGY The condition was originally recognised in the British Isles. The incubation period is 2.5 - 8 years. The disease occurs in adult cows with a peak incidence between four and six years of age as a result of animals being exposed as calves. It has principally been identified in Friesian/Holstein cross cows, but this probably reflects the high numbers of this type of animal in the British dairy herd. It has also been identified in Ayrshires, Guernseys, Jerseys, Shorthorns and their crosses. There have been several cases in beef suckler cows. Pregnancy and lactation do not appear to influence the time of onset of clinical signs. The greater incidence in animals produced from the dairy sector is a reflection of concentrate feeding to the calves. CLINICAL SIGNS The disease has an insidious onset which usually begins with a subtle change in temperament. Increasingly abnormal behaviour, accompanied by progressive locomotor disturbances are characteristic of the disease. Initially a farmer may notice that a previously quiet cow has become irritable and awkward to handle. For example the cow may be reluctant to enter the milking parlour and when it does it will often kick off the milk clusters. Abnormal behaviour includes repeated nostril licking, teeth grinding, attempts to scratch the head with hind cleats, rubbing against inanimate objects, aggression and general bullish behaviour. Locomotor disturbances include difficulty in rising, negotiating steps, tight corners or slippery surfaces. Ataxia, stiffness, paddling of the feet and hindleg hypermetria have also been recorded. Any attempts to handle or confine these animals e.g. by putting in a cattle crush usually amplify the clinical signs. There is usually evidence of trauma where cases have fallen over or rubbed themselves. Initially affected animals are often bright and eat well but latterly there is loss of condition and death is inevitable.LABORATORY DIAGNOSIS There is no laboratory test to confirm a diagnosis in the live animal. Laboratory investigations are only useful to rule out other possible diagnoses. DIAGNOSIS Not all cases of BSE will exhibit all the clinical features listed above, but as the disease is progressive, any clinical signs that are present will gradually become more marked. As such it may require more than one clinical examination to reach a provisional diagnosis of BSE. The pathogenesis is still being investigated. TREATMENT There is no treatment and the disease is invariably fatal. CONTROL There is a compulsory slaughter policy in the U.K. |
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