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Health
Transmissible spongiform encephalopathy of captive wild ruminants is thought to be a new disease. It was first reported in a British zoo in 1986. Since then, the disease has affected the eland, the Arabian oryx, the greater kudu, the gemsbok, the nyala, the scimitar-horned oryx, the ankole and the bison. Four ostriches in a zoo in Germany also developed a similar condition.
It is believed that these animals were infected in the same way as British cattle - through eating BSE-infected feed.
Feline spongiform Encephalopathy (FSE)
In 1990, a Siamese cat in the U.K. was diagnosed with a TSE. Since then, a large number of other cats have been affected. No evidence of a similar condition can be found in felines before that time.
Other felines now known to be affected are the puma, cheetah, ocelot and tiger. Again, the most likely explanation for the outbreak is that these animals were given BSE-infected feed.
Strangely, there is one case from Italy of a domestic cat and his human master both coming down with CJD at the same time. Research has shown that the agent responsible was the same for both cat and man. At the moment, there is no explanation for this.
Scrapie
Scrapie is a disease that mainly affects sheep. It is called "scrapie" because one of its early symptoms is restlessness in the sheep, leading to scratching, biting and scraping of the skin. The disease has been known to sheep farmers for more than 200 years.
Scrapie is believed to have originated in Spain and then spread to other parts of Europe. The widespread export of British sheep in the 19th century is thought to have spread the disease worldwide. Australia and New Zealand somehow escaped. Now, they employ strict quarantine measures for imported animals.
In areas where scrapie is already present, eradication measures have not been successful. This could be because the agent responsible for scrapie can live for many years on the grazing land. As a result, killing infected animals is not sufficient to wipe out the infection. Veterinarians do not know how scrapie is transmitted from one animal to another. Usually, only a small number of sheep in a herd are affected.
As with most TSE's, scrapie affects older animals, usually 4 years of age or more. Sheep with scrapie are irritable. They lose weight and tremble, then lose control of their hindquarters. The disease is always fatal. There have been no reported cases of human TSE caused by eating sheep.
Transmissible Mink Encephalopathy
Transmissible mink encephalopathy (TME) was first seen in 1947. Cases have turned up in Canada, the U.S. and Finland. The outbreaks occurred on mink farms where animals were fed meal made from the meat (muscle), bones and often the brains of other animals, including cattle and sheep (so-called offal). Some of the cases are blamed on ingestion of contaminated meal.
However, young mink fight among themselves and eat each other. The ingestion of a contaminated animal could be the cause of the epidemics seen on certain farms.
Chronic Wasting Disease of Deer and Elk
Deer and elk in the western U.S. and Canada suffer from another TSE called Chronic Wasting Disease of deer and elk (CWD). In parts of Colorado and Wyoming, 2 to 3 animals out of 100 are affected.
The abnormal prion in CWD is different from that in other TSE’s. However, one theory is that the disease originated in the 1960’s when deer were held in captivity in the same enclosure that had held scrapie-infected sheep. The infectious agent was present on the grazing land and crossed the species barrier to deer and elk.
As with scrapie, no cases of human TSE have been linked to eating deer and elk with CWD.
Bovine spongiform encephalopathy (Mad Cow Disease)
Bovine spongiform encephalopathy (BSE), also called Mad Cow Disease, was first identified in 1986 in the United Kingdom. The disease quickly spread through British herds. By 1993, when the disease peaked at 1000 new cases per week, 168,000 British cattle had died. Whole herds were slaughtered in an attempt to slow the spread.
A much smaller number of cases was also observed in Switzerland, France, Germany, Denmark, Portugal, Italy and Canada (1 animal). These cases were believed to be to be the result of the export of infected animals or infected cattle feed.
In 1988, the U.K. banned the feeding of offal to animals. As a result, by 1994 the number of cases had started to decrease.
There are two theories as to how this epidemic happened.
1. One theory is that the agent responsible for scrapie in sheep was found in the offal made from sheep remains and then ingested by bovines in their cattle feed. The abnormal prion responsible for scrapie was then altered in the bovines. Although the practice of feeding offal made from sheep had been around since the 1940’s, there was a change in the meat rendering practices in the U.K. around 1980. Organic solvents were no longer used, nor was the high degree of heat needed to remove the solvents. As a result, the theory suggests that the infectious prions were no longer being removed.
2. The second theory is that BSE is not a new disease in cattle but, in fact, a very old disease. Until 1980 it was extremely rare, affecting perhaps 1 cow in 20,000. Because it was so rare, it was not diagnosed as a distinct disease. Then in 1980, when the meat rendering practices no longer eliminated the infectious agent, it required only a few infected animals to infect the cattle feed and pass on the disease to thousands of animals.
In late 1995, doctors in the U.K. recognized a number of cases of human TSE that did not fit the description of classical Creutzfeldt-Jakob disease. The victims were much younger, the disease’s incubation period (development of the disease) was shorter, symptoms were different and people survived with the disease for a longer time. Eventually, it was proven that the abnormal prion in BSE was identical to the abnormal prion in this new human TSE.
Therefore it was concluded that these people had been infected by eating infected beef. This meant that for the first time BSE had been documented to have crossed the species barrier to humans.
This type of TSE has been termed new variant Creutzfeldt-Jakob disease (nvCJD). By early 1999, forty-one cases had been diagnosed, 40 in the U.K. and one in France.
Deer Farmers' Information Network
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