Animal Diseases
On Wednesday, March 20, 1996, "Mad Cow Disease" grabbed headlines worldwide. The shock waves were generated by a group of prestigious British scientists who revealed that the fatal cattle disease was likely being transmitted to humans. The news brought the British meat industry to a virtual standstill. English folk avoided the meat markets. The European Union and a cascade of other countries banned British beef. When the dust had settled, beef imports had been banned by 23 nations. Since 1986, autopsies of British cattle dying with mad cow disease revealed a nervous system infection that ate tiny holes in the brain. When viewed under a microscope, the brain actually looked like a sponge. This sponge-like appearance gave rise to the disease´s scientific name: Bovine Spongiform Encephalopathy or "BSE." This cumbersome name could literally be translated: cows´ (bovine) sponge-like (spongiform) brain disease (encephalopathy). The lay term, "mad cow disease," in addition to being much easier to pronounce and remember, also conveys the fact that infected cows often develop mental deterioration and behavioral abnormalities. "Formerly" docile animals become irritable, nervous, or aggressive. They often lose weight, and develop severe coordination problems before dying within two weeks to six months.
Beside being a terrible tragedy for the cattle population, BSE has powerful emotional appeal for other reasons. It is one of a group of fatal brain diseases that can be transmitted from one living creature to another. These diseases are technically called "transmissible spongiform encephalopathies." Many British consumers had apparently comforted themselves for years with the thought that it was unlikely for BSE to spread from cows to humans. However, even before March, 1996, there were serious concerns about human risk, because transmissible encephalopathies were known to affect many other animals besides cattle. Mice, sheep, goats, monkeys, pigs, mink, and other cattle have all come down with a spongiform encephalopathy when given meat from cattle that were known to have the disease. Roughly 20 animal species have been documented to come down with diseases resembling BSE. They are listed: cattle, mink, domestic cat, ostrich, sheep, mule deer, cheetah, monkey, pig, puma, mice, goats, elk, ocelot, gemsbok, Arabian oryx, nyala, greater kudu, eland, scimnar horned oryx.
One
might think that processed meat and bone meal from sheep or cows could
not carry any kind of serious infection. After all, carcasses are boiled
as part of the process of "rendering" that ultimately converts
the dead animals into feed for living creatures. It is true that the high
temperatures typical in that rendering process would be sufficient to
kill most disease-bearing organisms. However, the type of infectious agent
that is responsible for BSE is very unusual. Unlike most illnesses that
are caused by bacteria or viruses, BSE is caused by something called a
prion (pronounced "pree-on"). The destructive powers of prions
are outlined:
- Prions are infectious substances found in animal products used for animal
feed.
- They cause several typies of transmissible spongiform encephalophaty
diseases in humans and animals.
- These diseases are fatal, with no known cure.
Prions are very resilient proteins that are particularly worrisome because they are resistant to most forms of disinfection. They retain their infectivity even after normal sterilization procedures such as those using heat and ionizing radiation. In fact, prions are not even destroyed by temperatures well above the boiling point. In a laboratory test of the scrapie prion, some infectivity still remained after a full hour of exposure to dry heat at 680 degrees Farenheit. (360 degrees Celsius.). Prions are also impervious to freezing and drying. Much of the reason for their hardiness is no doubt related to their unusual composition. Prions have no genetic material and consist entirely of protein. They are composed of a complex combination of thousands of amino acids. Since some sterilization processes?like ionizing radiation?work by destroying an organism´s genetic material, prions can not be harmed by these measures.
For
more informations see:
- Proof
Positive by Neil Nedley