Mad Cow Disease
This is Sarah Long. And this is Steve Ember with SCIENCE IN THE NEWS, a VOA Special English program about recent developments in science.
Today, we tell about a disease in cows that can spread to other animals and to people. We also tell about recent scientific progress in developing a test for the disease.
The cattle disease is bovine spongiforn encephalopathy. It causes holes to develop in the brain. Cattle act strangely before they die. So it is known as Mad Cow Disease.
B-S-E first appeared in Britain in Nineteen-Eighty-Five, and has spread across much of Europe. All animals known to have the disease since that time have been found in Europe or imports from Europe.
Scientists believe that eating infected beef from a cow suffering B-S-E causes a similar disease in people. This deadly disease is called Creutzfeldt-Jakob Disease, or C-J-D. It cannot be cured. C-J-D is rare. It usually affects people sixty-five years old or older. More than one-hundred people in Europe have died or are dying from it. Most of the victims live in Britain.
Animal health experts recently met in Paris, France to discuss mad cow disease.
They said more than thirty countries have banned the import of meat, bone meal and live cattle from western Europe. They said countries can be considered at risk for B-S-E if they imported such products from Western Europe during the past twenty years. They said parts of Eastern Europe, Asia and the Middle East are at increased risk.
The officials also urged countries to approve measures to control the killing of animals for food. They say this would reduce the chance of infected meat being sold as food for people. They also said the human food supply should not include the animal parts thought most likely to carry the disease, such as the head and the spinal cord.
The European Union now requires that all animals over thirty months old be tested for mad cow disease when they are killed. The idea is that older animals are likely to have more severe infections that are the greatest danger to people.
American officials have taken steps to prevent Mad Cow Disease from entering the United States. The government restricts imports of cows and other animals from countries where B-S-E exists. Imports of some feed products from such areas also are restricted. Feed containing animal remains is suspected of causing the disease.
American officials say more than two-hundred-fifty experts know how to recognize foreign animal diseases, including B-S-E. Information about the disease has been provided to federal and state agencies, laboratories and some colleges.
American officials say they are inspecting animals for signs of B-S-E. Federal inspectors are examining all cows raised for meat. They examine the animals for disorders of the central nervous system. Any animal showing signs of such a disorder is destroyed. The meat is not permitted for use as human food. The brains of these animals are sent to the Agriculture Department for additional tests.
The only sure way to tell if an animal has B-S-E is to test a brain sample after it has been killed. Now, Israeli scientists say they have discovered the substance responsible for mad cow disease in the liquid waste of animals and people.
Scientists believe B-S-E is caused by a kind of infectious particle known as a prion (PREE-on). Prions are proteins. They do not contain any genetic material so they cannot make copies of themselves. This makes them different from all other known infectious agents such as bacteria, viruses, fungi and parasites.
Prions are found naturally in brain cells of people and animals. They do no harm. Sometimes, however, one changes shape. Other proteins known as enzymes can destroy normal proteins. But they cannot destroy changed prions.
A few years ago, scientist Stanley Prusiner showed how these changed prions act on surrounding normal prions to change them too. More and more prions change, until the changed ones are spread throughout the brain. This kills brain tissue and causes human spongiform brain diseases, including Creutzfeldt-Jakob disease.
Doctor Prusiner also showed that prion disease could move from one kind of animal to another. For example, he showed that people could develop C-J-D by eating meat from cows infected with B-S-E. Doctor Prusiner won the Nobel Prize for Medicine in Nineteen-Ninety-Seven for his work.
Ruth Gabizon was one of the researchers who worked with Doctor Prusiner. She continued her own research on human spongiform brain disease at the Hadassah University Hospital in Jerusalem, Israel. She was studying the part prions play in causing genetic Creutzfeldt-Jakob disease. This kind of C-J-D affects Jews whose families were from Libya.
The researchers on her team were looking for evidence of changed prions in liquid waste or urine. They studied the urine of small laboratory animals called hamsters, cattle and people. They tested the urine from animals and people infected with known prion diseases and from those who were healthy.
The kidneys contain urea, a substance that interferes with protein changing but does not destroy the proteins. The researchers suspected the prions might be changed by urea.
To test this idea, they put the urine samples from the animals and people into a machine that removes urea. This permitted the proteins to go back to their normal shapes. These proteins were then treated with enzymes that destroy normal proteins but not prions.
All the proteins were destroyed in the urine from healthy animals and people. But one protein survived in animals and people with prion diseases. The researchers said the presence of such a protein in urine is the way to tell if prion disease is present.
The Israeli scientists also infected some hamsters with prion disease. Tests of their urine showed the changed protein several weeks before signs of the disease first appeared.
A report of the Israeli research group's experiments will be published in the Journal of Biological Chemistry in September. However, the publication has already placed the research on its Internet web site.
Scientists who have seen the research say the experiment was simple and the results should easily be confirmed. Many laboratories all over the world are reportedly already trying to do this. If the results are confirmed, the new test could be used on groups of cattle. It could save uninfected cattle that are now killed after an infected animal is found.
The Israeli scientists say their test will be able to tell which people and animals are infected with spongiform disease before signs appear.
Other scientists say this could help make the blood supply safer around the world. It has not yet been proved that people with C-J-D can spread the disease by giving blood to other people. Yet officials are worried about that possibility. The American Red Cross will not accept blood from people who have lived in Britain for three months or in Europe for six months during the last twenty years.
The proposed test may also help answer questions about sick deer and other wild animals in the western United States and Canada. The animals are suffering a brain condition known as chronic wasting disease. The disease has spread among wild deer and elk. Researchers do not know how it is spread. But they say the new test could help discover the answer.
The Israeli scientists recognize that they are attempting to create a test for a disease that cannot be cured. In people, the period of time between infection and the first signs of the Creutzfeldt-Jakob disease may be as long as twenty or thirty years. Would people want to know if they are infected with the disease so many years before they would become sick? That is a question people may have to answer in the future.
For now, scientists say the new test may help them learn more about the prions responsible for spongiform disease before and after a person or animal becomes sick.
This SCIENCE IN THE NEWS program was written by George Grow and Nancy Steinbach. It was produced by Caty Weaver. This is Sarah Long. And this is Steve Ember. Join us again next week for more news about science in Special English on the Voice of America.