Ethics of Ignorance: Lessons From the Epidemiological Assessment of the Bovine Spongioform Encephalopathy ("Mad Cow Disease") Epidemic

Abstract

ETHICS OF IGNORANCE: LESSONS FROM THE EPIDEMIOLOGICAL ASSESSMENT OF THE BOVINE SPONGIOFORM ENCEPHALOPATHY ("MAD COW DISEASE '') EPIDEMIC ALFREDO MORABIA and MIQUEL PORTA * Background Since 1985, there has been an epidemic of bovine spongiform encephalopathy (BSE) or "mad cow disease" in the United Kingdom; cases have also occurred in other European countries including France, Switzerland, and Germany [I]. Anderson, et al., estimated that about 729,000 infected animals entered the human food chain in Great Britain before the end of 1995 [I]. This epidemic is thought to have originated from the transmission of the agent of BSE to cows through infected mean-and-bone fodder. It has still not been established whether the infectious agent originated from sheep suffering from scrapie or if BSE was a previously unrecognized sporadic disease in cattle. Since 1988, a series of official actions were taken in the U.K. BSE became a notifiable disease, use of ruminant-derived protein was banned from ruminant feed, and compulsory slaughtering and disposing of carcasses of all cattle suspected of having BSE was mandated [2]. In November 1989, specified bovine offal, including brain, spinal cord, and eyes were banned from human consumption and in 1990 from the feed of all animals and birds. The first suspicions of a possible risk for humans of BSE were directed toward Creutzfeldt-Jakob disease (CJD), a rare, rapidly lethal disease that shares many biological characteristics with BSE. At an advanced clinical stage, CJD produces a rapidly progressive dementia and myoclonus that is associated in about 60 percent of the cases with a characteristic electroenCorrespondence : Clinical Epidemiology Division, University Hospital, 25 rue Micheli-duCrest , 1211 Geneva 14, Switzerland. * Clinical Epidemiology Division, University Hospital, Geneva, Switzerland and Institut Municipal d'Investigacio Medica, Universität Autonoma de Barcelona, Spain, and School of Public Health, University of North Carolina at Chapel Hill.© 1998 by The University of Chicago. All rights reserved. 0031-5982/98/4102-1052$01.00 Perspectives in Biology and Medicine, 41, 2 ¦ Winter 1998 259 cephalographic spiking pattern. The histology ofthe brain reveals a spongiform encephalopathy. Many but by no means all scientists regard the agents of transmissible spongiform encephalopathies, which include BSE, CJD, and a new variant of CJD described below, as prions [2]. Prions are the modified, protease-resistant form of a normal protein named PrP [3]. Prions are generally thought to be infectious agents free of nucleic acid but Lasmézas, et al., have suggested that another agent, such as a nucleic acid, might be involved in transmission [3, 4] . Over 90 percent ofthe cases ofCJD are categorized as sporadic and have unknown causes. About 8 percent occur in high-risk families, and 2 percent are iatrogenic. In 1992, a European surveillance and research system was established in several countries, including France, Germany, Italy, Holland, Spain, and the U.K. All these countries had similar CJD incidence rates of about 0.5 to 1.0 case million per year in 1993. In 1994 and 1995, rates in Holland, France, and the U.K. had almost doubled. There are reasons to believe, however, that this increase is probably due to better detection of cases, specially among the elderly [5], The peak of the epidemic of BSE occurred in 1992 and incidence rates have been steadily declining since then. It has been predicted that the epidemic will disappear some time during the first decade of the next century [I]. The bovine epidemic was already well advanced in its decline when, in late 1995, ten cases of a new variant of CJD (vCJD) were identified from among the 207 cases of CJD neuropathologically examined since May '90 [6]. These cases were described in April 1996 in The Lancet [6]. It was reported that, in contrast to classic cases of CJD, these subjects were young (18 to 42 years), had mainly psychiatric symptoms, a slow evolution to death and characteristic histologic brain lesions [6]. On the basis of essentially clinical and pathological evidence, vCJD appeared to be a new disease. In March, 1996 the British government publicly announced that the risk of transmission to humans of the Bovine Spongiform Encephalopathy (BSE) , postulated by some scientists [7, 8] , could be real and that its clinical manifestation...