Bovine spongiform encephalopathy (BSE), or "mad cow disease", is one of these newly emerging diseases, and its mostly very rare disease. BSE is a transmissible, neurodegenerative, fatal disease of adult domestic cattle. It attacks the brain and central nervous system of the animal before eventually killing it. It usually takes four to six years for cattle infected with BSE to show signs of the disease, but ultimately is fatal for cattle within weeks to months of its onset.
History
BSE first came to the attention of the scientific community in November 1986 with the appearance in cattle of a newly-recognized form of neurological disease in the United Kingdom (UK). Between November 1986 and November 2002, 181 376 cases of BSE were confirmed in the UK.
Cause
• The nature of the BSE agent is still a matter of debate. According to the prion theory, the agent is composed largely, if not entirely, of a self-replicating protein, referred to as a prion. Another theory argues that the agent is virus-like and possesses nucleic acids which carry genetic information. Strong evidence collected over the past decade supports the prion theory, but the ability of the BSE agent to form multiple strains is more easily explained by a virus-like agent.
• The agent is highly stable, resisting freezing, drying and heating at normal cooking temperatures, even those used for pasteurization and sterilization.
• BSE was spread by cattle eating feed that contained meat-and-bone meal (MBM) made from BSE-infected tissues.
Transmissible Spongiform Encephalopathies
Transmissible Spongiform Encephalopathies (TSEs) are diseases characterized by spongy degeneration of the brain with severe and fatal neurological signs and symptoms. Example of these diseases:
• BSE is one of several different forms of transmissible brain disease affecting a number of animal species mostly cattle. Ruminant and feline species in zoos have been linked to BSE
• Scrapie is a common disease in sheep and goats.
• Human TSEs is divided in to:-
1. Creutzfeldt Jacob Disease {CJD}.
2. German-Straussler-Schinker Syndrome.
3. Fatal Familial Insomnia.
4. Kuru.
Variant Creutzfeldt-Jakob disease
• A newly recognized form of CJD, variant Creutzfeldt-Jakob disease (vCJD), was first reported in March 1996 in the UK. In contrast to the classical forms of CJD, vCJD has affected younger patients (average age 29 years, as opposed to 65 years), has a relatively longer duration of illness (median of 14 months as opposed to 4.5 months) and is strongly linked to exposure, probably through food, to BSE. Recent studies have confirmed that vCJD is distinct from sporadic and acquired CJD.
• The cluster of vCJD cases is due to the same agent that caused BSE in cattle.
Can sheep and goats get BSE?
There is a possible risk that BSE is in sheep and goat, and it could have been spread through the feeding of meat and bone meal (MBM) to farm animals. No goat that shows signs of any brain disease such as BSE is permitted to enter the food chain.
Treatment and Measures taken to Control BSE
• Treatment is ineffective.
• In July 1988, the UK banned the use of ruminant proteins in the preparation of animal feed.
• In 1994, the EU banned mammalian MBM to ruminants.
• In U.K. The practice of feeding MBM to cattle and all other farm livestock has been banned since 1996. This ban was subsequently extended across Europe in 2001.The USA has also banned the use of mammalian-derived proteins as a preventive measure.
• Within cattle herds, BSE is not contagious and does not spread from animal to animal. Isolated cases will not spark an epidemic if the affected cattle are destroyed and the carcasses are not recycled for use in feed of human or animal.
• The main control is the removal from the food chain of the parts of cattle most likely to contain BSE, (most notably the brain and spinal cord, related to the central nervous system). These parts are known as Specified Risk Material (SRM).
• From 1996 until November 2005 cattle aged over thirty months were simply banned from entering the food chain. But since November 2005, another control, the BSE testing of older animals was introduced. It means that cattle aged over 30 months at slaughter are allowed into the food chain only if they test negative for BSE. Testing helps to protect consumers from BSE because any animals found to be positive will be removed and destroyed.
• Prevention of cross contamination in slaughterhouses. An extremely small amount of the causative agent - less than one gram of brain 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
• However, the current BSE controls would not remove all of the possible infectivity, and it is not known whether it is possible for BSE to pass down through the generations.
1. NZFSA
http://www.nzfsa.govt.nz/consumers/food-safety-topics/animal-diseases/bse/index.htm
2. Merck
Book
3. The Food Standards Agency UK
http://www.eatwell.gov.uk/healthissues/factsbehindissues/bse/
4. WHO
http://www.who.int/mediacentre/factsheets/fs113/en/