Bovine Spongiform Encephalopathy – Сustom Literature essay

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Bovine Spongiform Encephalopathy Bovine spongiform encephalopathy (BSE) is a relatively new disease foundprimarily in cattle. This disease of the bovine breed was first seen in theUnited Kingdom in November 1986 by histopathological examination of affectedbrains (Kimberlin, 1993) . From the first discovery in 1986 to 1990 thisdisease 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 fourand five (Blowey, 1991). Due to the fact that BSE is a neurological disease, itis characterized by many distinct symptoms: changes in mental state 'mad-cow',abnormalities of posture, movement, and sensation (Hunter, 1993). The durationof the clinical disease varies with each case, but most commonly lasts forseveral 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 bilaterallysymmetrical, non-inflammatory vacuolation of neuronal perikarya and grey-matterneuropil was the scientists' overall conclusion (Stadthalle, 1993). Theselesions are consistent with the diseases of the more common scrapie family. Without further investigation, the conclusion was made that BSE was a new memberof 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 wasfound possible by the injection of brain homogenates from clinical cases(Swanson, 1990). This only confirmed that BSE is caused by a scrapie-likeinfectious agent. How does the transmission become so readily available among the entireUnited Kingdom feedlot population? Studies showed that the mode of infectionwas meat and bone meal that had been incorporated into concentrated feedstuffsas a protein-rich supplement (Glausiusz, 1996)

It is thought that the outbreakwas started by a scrapie infection of cattle, but the subsequent course of theepidemic was driven by the recycling of infected cattle material within thecattle population (Lyall, 1996). Although the average rate of infection is verylow, the reason why this led to such a large number of BSE cases is that much ofthe United Kingdom dairy cattle population was exposed for many, continuousyears (Kimberlin, 1993). To help control the outbreak, the British government in 1988 introduceda ban on the feeding of ruminant protein to other ruminant animals (Lacey, 1995).Such knowledge for the pathogenesis of the BSE disease shows precisely theactions that must be taken in order to control and minimize the risk ofinfection in healthy cattle around the world (Darnton, 1996). The appearance of BSE has made a sizable impact throughout much of theworld even though few countries, other than the United Kingdom, have experiencedpositive cases (Burton, 1996). The scare of an outbreak in other countries hasled to a great disruption in the trade economy, as well as other factorsconcerning each of the country's general welfare.

However, a rapid increase inthe understanding of the disease over the last four years leaves few unansweredquestions of major importance (Masood, 1996). BSE has been prevented, controlled and eradicated. As mentioned, BSE was first recognized in the United Kingdom and it isonly there that a large-scale epidemic has occurred (Burton, 1996). By the endof 1990 well over 20,000 cases of BSE had been has been confirmed in England, Scotland, and Wales (Filders, 1990). The deadly epidemic started simultaneouslyin several parts of the country and cases have been distributed over a wide areaever since (Cowell, 1996).

Besides the United Kingdom, cases of BSE have occurred in the Republicof Ireland. Some of these cases were associated with the importation of liveanimals, meat, and bone meal from the United Kingdom (Cherfas, 1990). Two cases of BSE have also occurred in cattle from the country of Oman. These animals were thought to be part of a consignment of fourteen pregnantheifers imported from England in 1985. Various cases have also been confirmedin Europe, Switzerland, and France (Patel, 1996). The economic consequences of BSE in the United Kingdom have beenconsiderable. At the beginning, the only losses due to BSE were those directlyassociated with the death or slaughter of BSE infected animals (Cowell, 1996).In August 1988, a slaughter policy with part compensation was introduced to helplessen the burden on individual farmers.

As the number of BSE cases increased, and more farmers were experiencing a second case, full compensation wasintroduced in February 1990 (Moore, 1996). In 1989 alone over 8,000 suspectedand confirmed cases of BSE were slaughtered. The compensation costs for theyear were well over 2.8 million pounds and the slaughter costs amounted to 1.6million pounds (Cockburn, 1996). Once studies had identified meat and bone meal as the vehicle ofinfection, the United Kingdom Government banned the feeding of all ruminant-derived protein to ruminants (Glausiusz, 1996). This had an immediate impact onthe cattle industry in terms of reduced exports and domestic sales of meat andbone meal (Hager, 1996).

In 1990, the Commission of the European Communitiesbanned the importation, from the United Kingdom, of all live cattle born beforeJuly 1988. Panic throughout the world caused many countries to entirely ban theimportation of all live cattle from the United Kingdom. Some even went as faras to ban the importation of milk and milk products (Hunter, 1993). BSE has also had economic consequences in the human food industries. Inthe winter of 1989/1990, the United Kingdom Government banned the use for humanfood of certain specified bovine meats which contained suspicious amounts of BSE(Cockburn, 1996). This ban was introduced as a precautionary measure to helpensure the risks to public health from BSE were kept to a minimum. Most of the information concerning BSE has come from extensive studiesof the scrapie agent.

The agent is small enough to pass through bacteriologicalfilters, thus demonstrating that it is virus-like or subviral in size (Kimberlin,1993). Unfortunately, the agent has other properties which are atypical ofviruses. The first contradiction is that infectivity is highly resistant tomany physicochemical treatments, such as heat, and exposure to ionizing or ultraviolet radiation (Swanson, 1990). Second, the disease does not induce an immuneresponse from the host (Stadthalle, 1993). These two controversies along withthe long incubation period explain why the scrapie group of agents have longbeen known as the 'unconventional slow virus' (Westgarth, 1994).

BSE is clearly not a disease of genetic origin. It has occurred in themajority of United Kingdom dairy breeds and their cross...

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