5 In 1986 the United Kingdom (UK) inherited a whirlwind of unprecedented proportions in bovine spongiform encephalopathy (BSE) or “Mad-Cow Disease.” Almost no one in the UK or elsewhere understood that this new veterinary disease would be momentous enough to transform international trade, topple ministers and perhaps governments, and present what is arguably the most complex epi- demiologic conundrum in history. The first cases of BSE in 1986 looked like rabies. However, the British Isles are free of rabies, and the brains of affected cattle did not contain the negri bodies found in animals that die of rabies. Affected cows exhibited anxiety, nervousness, and initial hyperactivity followed by lethargy. Most characteristic of the syndrome was, and is, “head-shyness.” Animals that were affected would not allow veterinarians and others to touch their heads. Attempts to examine the horns, horn sock- ets, or the ears were met with pronounced avoid- ance and obvious pain. Postmortem examination was unremarkable except for the consistent presence of vacuoles and astrocytic infiltration in the brain. The medulla oblongata area was spongy to the touch and micro- scopic examination revealed spongiform lesions or “holes” in the medullary region. The medulla con- tains areas that control gait, coordination, and involuntary movements such as breathing. These cows were suffering terribly and dying within a few days. None were recovering regardless of which treatment was initiated. Most were older dairy cows and were from the south of England. The British government wasted no time in marshal- ing the proper expertise to analyze the situation. Although not previously diagnosed in cattle, strik- ingly similar diseases had occurred in other species. Lumped under the collective term of transmissible spongiform encephalopathies (TSE), these diseases included scrapie in sheep, transmissible mink encephalopathy, and chronic wasting disease of mule deer and elk. In human beings, a trio of incurable diseases, Creutzfeldt-Jakob disease (CJD), Gerstmann- Straussler-Scheinker disease, and kuru, cause syn- dromes almost too horrific to contemplate but nonetheless are consistent with the TSEs of the ani- mal kingdom. The initial symptoms in people are self-neglect such as failure to properly groom, bathe, or eat. This rapidly progresses to profound apathy or irritability. Sleep disorders, disorienta- tion, and fatigue may supervene. Then serious intel- lectual deterioration such as inability to speak, rec- ognize objects, or read and write develop. Muscle spasms, palsies, and rigid paralysis usually occur together with bizarre visual disturbances. There is no treatment. Patients usually die within 1 year. Most of those affected are in their later 50s at onset. These diseases are quite rare and the incubation period can be very long—20 years or more in human beings. The shorter the natural longevity of a species the shorter the incubation period for TSEs. Cattle can be expected to develop the dis- ease in 4.5 to 5 years, sheep in somewhat less, and laboratory mice develop the disease in less than a year. Strains of wild mice that live longer may not develop the disease for 2 years. In human beings it is not possible to perform experimental work, but the incubation period has been deduced from a number of cases where people were exposed to contaminated brain electrodes or contaminated pituitary extracts from cadavers and developed CJD many years later. Kuru presents a more astonishing story. Natives of New Guinea who participated in a peculiar form of cannibalism that included eating the brains of their victims perpetuated kuru, a typical TSE, for many years. Cessation of cannibalistic practices has abolished the disease, but not until 30 years after the last brain was eaten. The cause of TSEs is an enigma within a mystery and what little is known is so complicated as to elude the comprehension of all but a few. Early the- ories suggested that this class of diseases might be ARTICLES Bovine spongiform encephalopathy Lester M. Crawford, DVM, PhD Washington, D.C. From Association of American Veterinary Medical Colleges. Reprint requests: Lester M. Crawford, DVM, PhD, Georgetown University, Center for Food and Nutrition Policy, 3240 Prospect St., NW, Washington, DC 20007. AJIC Am J Infect Control 1998;26:5-7. Copyright © 1998 by the Association for Professionals in Infection Control and Epidemiology, Inc. 0196-6553/98 $5.00 + 0 17/46/84713
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