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Eight questions consumers should ask on the threat of mad cow disease

The World Health Organization is today publishing a new document to assist governments, consumers associations and other concerned organizations to protect consumers from the dangers of consuming beef infected with Bovine Spongiform Encephalopathy (BSE or "mad cow disease). The document provides governments and others involved in consumer protection with background information on the disease and how to prevent its spread.

BSE, or “mad cow disease”, is a new disease from a mysterious family of related and mostly very rare diseases. Cases in cattle were first reported in the United Kingdom in 1986. In 1996, another new disease, variant Creutzfeldt-Jakob Disease, or vCJD, was detected in humans and linked to the BSE epidemic in cattle. Consumption of contaminated meat and other food products from cattle is presumed to be the cause.

Both diseases pose many difficult scientific challenges. Answers to all questions cannot be given with absolute certainty. However, a great deal is now known about the origins of the BSE epidemic, the reasons for its spread, the tissues that are most dangerous to consume, and the likely reasons for the appearance of a related disease in humans. Most importantly, intense research, backed by practical experience, has defined a series of measures that countries can use to keep the causative agent out of the food chain and thus ensure the safety of the meat supply. When all appropriate measures to minimize human exposure are fully implemented and controlled, meat and meat-based products derived from cattle can be regarded as free from the BSE agent and thus free from any risk of causing vCJD in humans.

Here are some of the most important questions for consumers to ask their national public health and veterinary authorities. These questions are most important in countries where BSE cases have been reported. However, in view of the long incubation period and the fact that contaminated feed has been widely distributed in international trade, consumers and governments in other countries would be wise to consider these questions as well.

What are cattle being fed?

BSE is clearly linked to the practice of recycling bovine carcasses to recover so-called “meat and bone meal” protein, and then feeding this protein back to other cattle. If cattle are not being fed protein derived from the carcasses of ruminants (cattle, sheep and goats), there is virtually no risk of BSE. If ruminant protein is fed only to pigs and poultry, and if this feed has no chance to mix with and contaminate cattle feed, at feed mills or on the farm, the risk of BSE in the country is insignificant.

Does the government have a system of active surveillance for BSE?

The recent introduction of rapid screening tests, compulsory in many countries, has greatly improved the detection of cases. Such “active” detection of infected cattle, followed by their destruction, prevents entry into the feed chain of a large proportion of infectious material. News of a few cases in countries with active surveillance is more reassuring than no reported cases in countries with poor surveillance.

Are cases of BSE imported or are they being born within the country’s herds?

Within cattle herds, BSE is not contagious and does not spread from animal to animal. Isolated imported cases will not spark an epidemic if the affected cattle are destroyed and the carcasses are not recycled for use in feed. Of much greater concern are cases of BSE in cattle born within the national herd, as this implies that feeding practices within the country are at fault and that many other cattle have been exposed.

Does meat come from young cattle?

The incubation period for BSE is very long: 4–5 years. During this period, cattle exposed to the BSE agent show no symptoms and, until late in the period, have no infectious material in their tissues. If cattle are slaughtered at a young age (preferably under 30 months), the likelihood that veal or beef and other bovine products can transmit vCJD is greatly reduced.

Are high-risk tissues removed and destroyed?

The agent that causes BSE is not distributed evenly throughout the animal’s body, but is concentrated in certain tissues, most notably the brain and spinal cord, related to the central nervous system. Stringent slaughter practices that remove and destroy these high-risk tissues have an immediate impact on food safety and can protect consumers even when BSE is established within a country.

Are procedures in place to prevent cross-contamination in slaughterhouses?

The agent that causes BSE, and presumably vCJD, has never been detected in bovine skeletal muscle tissues, from which most quality meat is derived. However, an extremely small amount of the causative agent – less than one gram of brain (the size of a peppercorn) from diseased cattle – is sufficient to cause infection in cattle. For humans, the amount capable of causing infection is unknown but could likewise be very small. For this reason, it is vital to guard against cross-contamination. Safe slaughterhouse practices ensure that high-risk materials have no chance to come into contact with otherwise safe materials and contaminate them.

Are there any other meat products that could contain BSE?

The use of wire brushes and other mechanical tools to recover meat scraps attached to bones and the vertebral column can pull out infectious nervous tissue and contaminate meat that is otherwise safe. Such “mechanically recovered meat” is used in processed meat products. Some experts believe that the BSE agent was transmitted to humans through products containing mechanically recovered meat contaminated with nervous tissue. Techniques that prevent the inclusion of nervous tissue in mechanically recovered meat confer important protection, particularly in high-risk countries.

Are safe practices stringently controlled?

It is not sufficient to recommend safe practices. Such practices must also be rigorously enforced, ideally through legislation, and controlled through inspection by veterinary and food authorities.

Safe to eat – On the basis of current knowledge, scientists agree that some bovine products are safe, regardless of the BSE status within a given country. Bovine products considered safe to eat or use include milk and milk products, gelatin prepared exclusively from hides and skins, and collagen prepared exclusively from hides and skins. Infectivity has never been detected in skeletal muscle tissues, from which most quality meat is derived. A number of scientists believe that skeletal muscle meat is as safe to consume as milk and milk products, provided that such meat has not been contaminated during slaughterhouse procedures.

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For more information contact:

Mr Iain Simpson
Telephone: +41 22 791 3215
Mobile phone: +41 79 475 5534
E-mail: simpsoni@who.int