Mad Cow Disease: Overview

BSE (often referred to as “mad cow disease”) and variant and classic CJD belong to the unusual group of progressive, degenerative neurological diseases known as transmissible spongiform encephalopathies (TSEs). These diseases are characterized by a long incubation period of up to several years, during which there is no visible indication of the disease. The incubation period for BSE among cattle ranges from three to eight years; for vCJD among humans, the incubation period is unknown, but is at least five years and could extend up to 20 years or longer. The diseases are invariably fatal; there is no known treatment or cure.

It is believed that vCJD may be acquired from eating food products containing the BSE agent, and there is strong epidemiologic and laboratory evidence for a causal association between vCJD and BSE. The absence of confirmed cases of vCJD in geographic areas free of BSE supports a causal association. BSE and vCJD have never been identified in the United States.

BSE among cattle was first described in the U.K. in November 1986. Epidemiological evidence established that the outbreak of BSE was related to the production and use over many years of contaminated meat-and-bone meal. The source of the BSE outbreak is uncertain. There is strong evidence and general agreement that the outbreak was amplified by feeding rendered bovine meat-and-bone meal to young calves.

The vast majority of BSE cases have been reported in the U.K. Through November 2000, about 177,500 cases of BSE have been confirmed there in more than 35,000 herds of cattle. The U.K. epidemic peaked in January 1993 at nearly 1,000 new cases per week. Surveillance in Europe has also led to the identification of cases of BSE in Belgium, Denmark, France, Ireland, Liechtenstein, the Netherlands, Portugal and Switzerland and, most recently, in Germany, Spain and Italy. From 1995 through early December 2000, 88 human cases of vCJD were reported in the U.K, three in France and one in Ireland.

European countries have instituted a variety of public health control measures, such as BSE surveillance, the culling of sick animals, the banning of specified risk materials (SRMs), or a combination of these, to prevent potentially BSE-infected tissues from entering the human food chain. Due to its early outbreak, the most stringent of these measures have been applied in the U.K. In June 2000, the European Union Commission on Food Safety and Animal Welfare adopted a decision requiring all member states to remove SRMs from the animal feed and human food chains as of October 1, 2000; such bans had already been instituted in most member states.

Source: Department of Health and Human Services