After it was confirmed by a British laboratory that an eight-year-old cow in the US was infected with mad cow disease, the question of US beef imports became a political issue in Taiwan.
In 1985, 133 dairy cows in the UK died after becoming unable to coordinate their movements properly and losing strength in their back legs. The brain tissue in many of these cows showed spongelike pathological changes. The following year, the British government declared that these cows had bovine spongiform encephalopathy (BSE). By 1996, about 170,000 cows had been infected. The British government, recognizing the seriousness of the issue, slaughtered all cattle 30 months and older, altogether 5 million head. As a result of these measures, the EU once again began importing British beef in 2000.
In 1994 and 1995, ten cases similar to the Creutzfeldt-Jakob Disease (CJD), which only affects humans, were found in the UK. Human CJD normally affects people above the age of 50, and infected brain tissue shows porous pathological changes. CJD is hereditary, but can also occur as a result of organ transplants, blood transfusions or hormone use. The 10 cases found in the UK differed from traditional CJD. It occurred in people below 40 years of age without a family history of the disease and who had not had organ transplants. Furthermore, the pathological changes in their brain tissue were very similar to the pathological changes connected to BSE, and it was therefore called "new variant CJD" (nvCJD).
In 1997, five more cases occurred in the UK and one in France. The British government felt that the situation was serious and announced that beef intake could be related to nvCJD, but there is as of yet no proof of this.
It is currently thought that the cause of the disease is a mutated protein named prion, which was discovered by the US neurobiologist Stanley Prusiner in 1982. Prion is a peptide made up of between 27 and 30 amino acids, and which is a constituent of the normal cell membrane. Prion is resistant to enzymes, high heat and infrared radiation, and unlike bacteria or viruses it does not contain nucleic acids to be used in the production of newer generations.
After infecting animals, however, its presence in the brain will gradually increase and cause porous pathological changes in the brain tissue. The only diagnostic method currently available is to kill an animal and rely on pathohistological sections from the brain and immunochemistry staining.
Because sheep with scrapie -- a usually fatal disease of the nervous system particular to sheep -- are heavily laden with prion, BSE-infected cows were infected by scrapie-infected meat and bone meal feed made from sheep. There have been reports of sable, deer and cats fed with meat and bone meal feed having similar diseases.
As a result, the World Organization for Animal Health (OIE) banned the use of meat and bone meal feed to feed ruminants in order to eliminate contamination through the food chain. The US and Taiwan banned meat and bone feed for ruminants in 1997, and the cows that now have been diagnosed with BSE in the US were all born before the imposition of the ban.
Epidemiological experts have made a mad dow disease infection risk analysis, showing that 64.1 percent of the time infected animals had brain infections, 3.3 percent intestinal infections, but that the disease did not infect the flesh. Experts estimate that someone who eats a steak in the UK runs a risk of one in 10 billion.
After the appearance of BSE in 2003, the US changed its method of killing animals. It banned the practice of incapacitating cattle by injecting powerful blasts of air into their brains with pneumatic air stunners just before they're slaughtered, because that might splatter brain tissue throughout the carcass.
It is impossible to demand a zero-risk standard for foodstuffs, and the OIE's legal foundations are often amended due to new scientific findings.
Recent research has showed that boneless beef from beef cows younger than 30 months runs almost no risk of transmitting BSE. As a result, regulations have once again been amended. Since the UK first announced BSE, only 161 people around the world have been infected by nvCJD. Current monitoring of BSE is becoming ever stricter, and the risk of infection is small.
The number of people who have died from other diseases and the harm created by infected foods are innumerable, while the number of BSE-infections is so small as to be almost insignificant. So should we destroy all the US beef that already has been imported? We must all decide for ourselves whether or not we want to eat that tasty US beef.
Lai Shiow-suey is a professor in the department of veterinary medicine at National Taiwan University.
Translated by Perry Svensson
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