Bovine Spongiform Encephalopathy

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Bovine Spongiform Encephalopathy

Bovine spongiform encephalopathy (BSE) is a relatively new disease found primarily in cattle. This disease of the bovine breed was first seen in the United Kingdom in November 1986 by histopathological examination of affected brains (Kimberlin, 1993) . From the first discovery in 1986 to 1990 this disease developed into a large-scale epidemic in most of the United Kingdom, with very serious economic consequences (Moore, 1996).

BSE primarily occurs in adult cattle of both male and female genders. The most common age at which cows may be affected is between the ages of four and five (Blowey, 1991). Due to the fact that BSE is a neurological disease, it is characterized by many distinct symptoms: changes in mental state 'mad-cow', abnormalities of posture, movement, and sensation (Hunter, 1993). The duration of the clinical disease varies with each case, but most commonly lasts for several weeks. BSE continues to progress and is usually considered fatal (Blowey, 1991).

After extensive research, the pathology of BSE was finally determined. Microscopic lesions in the central nervous system that consist of a bilaterally symmetrical, non-inflammatory vacuolation of neuronal perikarya and grey-matter neuropil was the scientists' overall conclusion (Stadthalle, 1993). These lesions are consistent with the diseases of the more common scrapie family. Without further investigation, the conclusion was made that BSE was a new member of the scrapie family (Westgarth, 1994).

Transmission of BSE is rather common throughout the cattle industry. After the incubation period of one to two years, experimental transmission was found possible by the injection of brain homogenates from clinical cases (Swanson, 1990). This only confirmed that BSE is caused by a scrapie-like infectious agent.

How does the transmission become so readily available among the entire United Kingdom feedlot population? Studies showed that the mode of infection was meat and bone meal that had been incorporated into concentrated feedstuffs as a protein-rich supplement (Glausiusz, 1996). It is thought that the outbreak was started by a scrapie infection of cattle, but the subsequent course of the epidemic was driven by the recycling of infected cattle material within the cattle population (Lyall, 1996). Although the average rate of infection is very low, the reason why this led to such a large number of BSE cases is that much of the United Kingdom dairy cattle population was exposed for many, continuous years (Kimberlin, 1993).

To help control the outbreak, the British government in 1988 introduced a ban on the feeding of ruminant protein to other ruminant animals (Lacey, 1995). Such knowledge for the pathogenesis of the BSE disease shows precisely the actions that must be taken in order to control and minimize the risk of infection in healthy cattle around the world (Darnton, 1996).

The appearance of BSE has made a sizable impact throughout much of the world even though few countries, other than the United Kingdom, have experienced positive cases (Burton, 1996). The scare of an outbreak in other countries has led to a great disruption in the trade economy, as well as other factors concerning each of the country's general welfare. However, a rapid increase in the understanding of the disease over the last four years leaves few unanswered questions of major importance (Masood, 1996). BSE has been prevented, controlled and eradicated.

As mentioned, BSE was first recognized in the United Kingdom and it is only there that a large-scale epidemic has occurred (Burton, 1996). By the end of 1990 well over 20,000 cases of BSE had been has been confirmed in England, Scotland, and Wales (Filders, 1990). The deadly epidemic started simultaneously in several parts of the country and cases have been distributed over a wide area ever since (Cowell, 1996).

Besides the United Kingdom, cases of BSE have occurred in...
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