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BSE is a fatal central nervous system disease first identified in the U.K. in 1986. Affected cows show increased apprehension, poor coordination, difficulties in walking, and weight loss. The infections that cause BSE apparently existed for several years before the disease was recognized.
BSE is not limited to Britain. It has been found in native cattle in France, Switzerland, Northern Ireland, the Republic of Ireland, the Channel Isles, and the Isle of Man. Cattle exports carried the disease to Canada, Denmark, Oman, and the Falkland Islands. Moreover, at least 100,000 cattle whose BSE status is unknown have been shipped from the U.K. to other countries. Most of these animals are unaccounted for.
Scientists put the blame for BSE on the practice of feeding cattle the remains of sheep infected with scrapie, a disease with many similarities to BSE and whose name comes from the fact that affected animals develop a persistent itch that causes them to scrape off their wool or hair. It has been recognized in Britain since at least 1730, and an estimated one-third of British flocks are currently affected by scrapie. It is also endemic in U.S. sheep. The disease persists in cattle herds when they are fed the remains of BSE-infected cattle, as was common in the U.K. and continues in the U.S.
The infectious agent in scrapie and BSE is not a virus or bacterium, but a faulty protein, called a prion (pronounced: pree on ), discovered by Stanley B. Prusiner of the University of California at San Francisco. Disease-causing prions are proteins that are normal in their molecular make-up, but abnormal in their shape, like springs that have been bent out of their normal configuration. They can distort the normal proteins in brain and nerve cells, turning them into disease-carriers as well. A teaspoonful of tainted cattle feed is believed to be all it takes to give a cow BSE.
Cattle remains in animal feed in the U.K. have also spread encephalopathic diseases to domestic cats, captive wild cats (puma, cheetah, ocelot), and captive wild ruminants (nyala, gemsbok, eland, Arabian oryx, greater kudu, scimitar-horned oryx). An infected mother kudu apparently passed the infection to her newborn, who came down with symptoms at 19 months, never having had contact with contaminated feed or other sick animals
Prions that cause bovine spongiform encephalopathy are believed to be the culprits in some cases of Creutzfeldt-Jakob disease (CJD), the most common transmissible encephalopathy in humans. CJD was first identified in the 1920s. It can take as long as 30 years for the disease to manifest, but it proceeds quickly once symptoms start. In weeks to months, affected individuals lose mental faculties and muscle coordination, pass into a coma, and die. CJD has been found in the U.S., Britain, France, Italy, Chile, Czechoslovakia, Hungary, Israel, and Japan.
The disease is similar to kuru, which was identified in 1957 in the Fore highlanders of Papua, New Guinea, who apparently contracted it as a result of eating the brains of the deceased. Cannibalism has stopped in New Guinea, and kuru has virtually disappeared.
There are also two inherited forms of human prion diseases.
Several studies have linked CJD with exposure to animals. The risk of CJD appears to be higher in those who have had contact with rabbits, mink, ferrets, deer, or other wild animals, or have eaten pork, rare meat, or the brains of sheep or wild game. The cases receiving the most recent attention in the U.K. are those of young people (ten cases so far) and dairy farmers (four so far), all of whom had eaten beef products in the preceding ten years, although one later became a vegetarian in 1991. British medical authorities believe that the most plausible interpretation of events is that consumption of meat from affected cattle is the cause of these recent cases. The new cases appear to be slightly different from typical CJD, which supports the concern that a new variant of CJD is afoot.
CJD has also been accidentally transmitted from person to person in the course of medical treatments. It was given to 2 patients through brain electrodes and 23 patients by injections of growth hormone taken from cadavers, and has been passed in transplanted tissues. Three pathology technicians became infected, presumably by contact with human tissues. Brain and nerve tissues seem to be the most dangerous tissues, but other organs and body fluids are also potentially infective.
The prions that cause CJD are not destroyed by typical chemical or heat disinfectant methods used in hospitals. Heating to 134 degrees Celsius (273 degrees Fahrenheit) does not reduce its infectivity. In fact, studies indicate that NO amount of cooking will destroy the prion.
Figures from 1979 to 1990 show that CJD was listed on death certificates of 2,614 people in the U.S. The great majority are over 50 (the mean age was 67), but 23 were in their 30s and 3 were in their 20s. About 10 percent of cases are hereditary, passing as a dominant trait. The reported cases are probably underestimates, as many cases are probably misdiagnosed and CJD is not a reportable disease.
Foodborne cases of CJD that might occur in the U.S. will not necessarily mirror the clinical features of their British counterparts, as spongiform encephalopathies exist in several forms, and prions occur in different strains / Emerging cases of CJD in Britain affect a younger age group and have somewhat different clinical signs and electroencephalographic tracings
In a degenerative disease in cows called, Bovine Spongiform Encephalopathy, the causative organism eats holes in the cows brain tissue, which causes abnormal behavior and results in death. But questions remain as to whether recent European cases of Creutzfeldt Jakob disease, a human spongiform, are linked to exposure to cattle with Bovine Spongiform Encephalopathy. In the 1970's a change in animal waste disposal, in which sheep wastes were fed to cows could have provided a pathway of transmission, infecting the cattle. One explanation for this disease, in humans, includes the mutation of prion proteins causing them to eat away at neurons. There are a number of alternative theories.
Question: "If I lived in the UK prior to 1996, can I donate blood in the U.S.?"
Answer: No. A recent decision (Sept 1999) bars it.
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2. Marsh RF. Bovine spongiform encephalopathy: a new disease of cattle? Arch Virol 1993;7(Suppl):255-9.
3. Prusiner SB. The prion diseases. Scientific American, Jan. 1995, pp. 48-57.
4. Bleem AM, Crom RL, Francy B, Hueston WD, Kopral C, Walker K. Risk factors and surveillance for bovine spongiform encephalopathy in the United States. JAVMA 1994;204:644-51.
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10. Marsh RF, Bessen RA. Physicochemical and biological characterizations of distinct strains of the transmissible mink encephalopathy agent. Phil Trans R Soc Lond B 1994;343:413-4.
11. Miller LD, Davis AJ, Jenny AL. Surveillance for lesions of bovine spongiform encephalopathy in US cattle. J Vet Diagn Invest 1992;4:338-9.
12. Centers for Epidemiology and Animal Health, Animal and Plant Health Inspection Service, US Department of Agriculture. United States rendering and feed-manufacturing industries: evaluation of practices with risk potential for bovine spongiform encephalopathy. USDA, Fort Collins, CO, February 1990.
13. Feeds and Nutrition. Second Edition, Ensminger Publishing Co, Clovis, California, 1990, pp. 250-1.
14. Ibid, p. 410.
15. Ibid, p. 259-60.
16. Ibid, p. 260.
17. Ibid, p. 412.
18. Ibid, p. 545.
19. United States Department of Agriculture. Questions and answers about bovine spongiform encephalopathy (BSE). 1996.
20. Robinson MM, Hadlow WJ, Huff TP, et al. Experimental infection of mink with bovine spongiform encephalopathy. J Gen Virol 1994;75:2151-5.
21. Marsh RF, Bessen RA. Epidemiologic and experimental studies on transmissible mink encephalopathy. Dev Biol Stand. Basel, Karger 1993;80:111-8.
22. Collinge J, Rossor M. A new variant of prion disease. Lancet 1996;347:916-7.
23. Feeds and Nutrition, op. cit., pp. 184-5 and 258.