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Bovine spongiform encephalopathy (BSE)

BSE is one of a group of brain wasting diseases known as transmissible spongiform encephalopathies (TSEs). It occurs in adult cattle and was first identified in Britain in 1986.

New Zealand has never had a case of bovine spongiform encephalopathy (BSE) and has been recognised as BSE free by the World Organization for Animal Health (the OIE).

Understanding the BSE threat

New diseases continue to emerge in animals and people. In the last decades of the 20th century, more than 30 new diseases - including HIV/AIDS and Ebola haemorrhagic fever – were detected for the first time in history. BSE, or ‘mad cow disease’, is one of these newly emerging diseases. Its related human form, variant Creutzfeldt-Jakob disease (vCJD), is another.

Creutzfeldt-Jakob disease (vCJD) – frequently asked questions [Ministry of Health]

BSE 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, our scientific understanding of these diseases has progressed dramatically in recent years and 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.

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.

The following are important factors for the protection of a country's BSE status and consumer health.

Cattle feed and BSE

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

Surveillance for BSE

The introduction of rapid screening tests, compulsory in many countries, has greatly improved the detection of cases. Such ‘active’ detection of infected cattle in countries where BSE has been identified, followed by their destruction, has prevented entry into the feed chain of a large proportion of infectious material. This has greatly reduced the number of cases in those countries where BSE has been found. BSE is disappearing globally following the implementation of control measures.

New Zealand's TSE preventive/surveillance programme

The spread of BSE within cattle herds

BSE is not contagious and does not spread from animal to animal.

The age at which cattle are slaughtered for meat

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

Removal of high risk tissues from BSE infected cattle

The agent that causes BSE is not distributed evenly throughout the infected animal's body. It is concentrated in certain tissues related to the central nervous system, particularly the brain itself and spinal cord. Stringent slaughter practices that remove and destroy these high-risk tissues have been adopted where necessary and have had an immediate impact on food safety, protecting consumers even when BSE is established within a country.

Prevention of 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 high-risk materials have no chance to come into contact with otherwise safe materials and contaminate them.

Are bovine products safe to eat?

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

Related links

Frequently asked questions about BSE and TSEs [Biosecurity New Zealand]

NZFSA updates BSE importing requirements – media release, February 2007