Mad Cow Disease: Know the Risks
Years after it was supposedly vanquished, the brain-eating disease that kills cows and some people who eat them is on a comeback. Today, the mad cow disease or bovine Spongiform Encephalopathy (BSE) is again breaking headlines and is stirring a lot of havoc and public fear all around the globe. Here are some of the most frequently asked questions and answers regarding BSE.
Q. What exactly is BSE?
A. BSE or mad cow disease is one of the several fatal brain diseases called transmisshible sponfigorm encephalopathies (TSEs). BSE is a progressive lethal central nervous system disease of cattle. The brain looks like a sponge hence the term spongiform because the brain contains vacuoles. In 1982, Stanley Prusiner, a biochemist at the University of California suggested a radical idea- that various encephalopathies were caused by a rouge protein- a prion.
Q. What are prions?A. Prions or PrP proteins are abnormal rouge proteins able to convert normal proteins into more abnormal forms. They contain no nucleic acirs (DNA or RNA). They consist of single molecule containing about 250 amino acids, termed the PrP protein.
Abnormal PrP proteins are folded in a way that allows them to resist normal protease degradation. Overtime, this results to a build-up of aggregates of PrP, especially in neurons in the brain.
Q. Is there a risk that BSE will infect people?
A. Yes . The TSEs were once considered unlikely to infect other species. However, in 1996, the UK government acknowledged that eating contaminated meat was the most likely explanation why 10 young people had the variant Creutzfeldt-Jakob disease (VCJD). The awkward name reflects the similarity to Creutzfeldt-jakob disease (CJD) a deadly brain illness that strikes about one person per million per year due to genetic or unknown causes.
While CJD mainly affects the elderly, vCJD appears among younger people. The quick and gruesome death starts with mood swings, numbness, and uncontrolled body movements. Eventually, the mind is destroyed somewhat like Alzheimer’s another brain-wrecking disease. Many vCJD victims die four months after symptoms appear. There is no treatment.
Q. What about TSEs in other animals?
A. Scrapie is the TSE disease in sheep and goats. Mink and North American mule deer and elk can contract TSEs. A neurological disease in household cats and in ruminant and feline species in zoos has been linked to BSE. Most cases in such animals appears to have occurred in the UK.
Q. what is the infectivity of BSE- containing material?
A. Infection is dose dependent but the required dose for BSE transmission to cattle is small. If consumed 500mg to 1 g infected brain appears sufficient to infect. The BSE agent has been found only in the brain tissue, spinal cord and retina of cattle naturally affected with BSE. It has not been found in meat or milk. Similarly it is not transmissible through meat or milk. Traces of the BSE agent are detectable in the small intestines of calces that had been fed large doses of meal from BSE-infected animals.
Q. What about the safety of human and veterinary vaccines made from bovine products?
A. The World Health Organization (WHO) reported that human and veterinary vaccines from bovine materials carry the risk for transmission of animal TSE agents. It was recommended that the pharmaceutical industry avoid the use of bovine materials and materials from other animal species in which TSEs occur. These include nine vaccines regularly given to millions of American children, including common vaccines to prevent polio, diphtheria and tetanus. These precautions apply to the manufacture of cosmetics as well.
Q. Can vCJD be transmitted through blood transfusions?
A. In 1997, new animal studies suggested that vCJD could be transmitted through the blood. White blood cells, which form part of the immune system and are found in the lymph glands, were isolated as one of the high risk tissues for BSE infection. As a result of this concern the British government required the removal of white blood cells from donated blood.
The fact that vCJD could enter the lymph system raised further possibility that it might infect the tonsils or appendix both of which contain large amounts of lymphoid tissue.
Q. How long is the incubation period of vCJD?
A. The incubation period is yet unknown. Some experts believe that it could be as long as 30-40 years. In August last year, a new research indicated the existence of a hidden subclinical form of BSE which produced no symptoms but could nonetheless be infectious . This raised the frightening possibility that not only cattle but sheep, pigs and poultry exposed to BSE via animal feed may secretly harbour the disease.
Q. When did the BSE outbreak start?
A. The illness was first identified in 1985 by a vet who was puzzled by the odd symptoms exhibited by sick cows in a dairy farm in Southern England. Scientist found evidence linking the new illness to the sheep disease – scrapie. It was technically named Bovine Spongiform Encephalopathy (BSE) but it became popularly known as mad cow disease – because of the way infected cattle behaved.
Scientists believed that BSE was created when cows were fed scrapie-infected feeds manufactured from abattoir offcuts. Experts theorized that new manufacturing techniques in feed production in the 1970s and 1980s allowed a resilient strain of scrapie to enter the feed and for it to re-emerge in a new form in cattle disease –BSE.
Q. How widespread is the BSE outbreak?
A. The WHO says that approximately 180000 cases of BSE have been reported in Britain and relatively small numbers of BSE cases (in total approximately 1300) have also been reported in native cattle in Belgium , Denmark, France, the Republic of Ireland, Liechtenstein, Luxembourg, the Netherlands, Portugal and Switzerland.
Germany and Spain reported their first native cases in November 2000. A couple of dozen cases have also been reported in Canda, the Falkland Islands (Islas Malvinas), Italy and Oman.
Q.What are the measures that can reduce exposure to the BSE agent?
A. Here are the mesures that are recommended by Who to reduce exposure to the BSE agent:
a) all countries must prohibit the use of ruminant tissues in ruminant feed and must exclude tissues that are likely to contain the BSE agent from any animal or human food chain.
b) This means that brain tissue , spinal cord, intestines should not be eaten. That is, they should not be used in preparing “nilagang baka” ‘ “sisig” and “goto”.
c) All countries are encouraged to conduct risk assessments to determine if they are at risk for BSE in sheep and goats. It is advised that any tissue which may come from deer or elk with chronic wasting disease (CWD a transmissible spongiform disease of North American mule deer and elk) is not used in animal or human food. However, there is no evidence to suggest that CWD in deer and elk can be transmitted to humans.
d) No infectivity has yet been detected in skeletal muscle tissue. For one’s own peace of mind , nervous and lymphatic tissues from animals suspected of having BSE, should be removed.
Source: BAR Today Jan mar 2001 issue, Junelyn S. De la Rosa