Bovine spongiform encephalopathy
By Kevin Pan
Transmissible spongiform encephalopathies are known as prion diseases that are progressive neurological disorders. This group of diseases includes Kuru, which is a disease found among New Guinea natives, Gerstmann-Straussler-Scheinker disease and bovine spongiform encephalopathy. Bovine spongiform encephalopathy is a progressive neurological disorder in cows that arose in the 1980’s.. BSE has an incubation period of about four years and affects adult cattle at the peak onset of 4-5 years. Humans can be infected with this disease after eating products that have been tainted with this disease. While the exact method of transfer is still not understood, the disease is not believed to be a product of bacteria, viruses, parasites and fungus (eden.lsu). It is believed that a misfolded protein known as the prion protein in cattle is the cause of transfer. Prion proteins are commonly found throughout the body, but they can be modified if there is an accumulation of the modified prion proteins (edeu.lsu). Eventually, a high accumulation of these protein can lead to damaged and disease. A major issue with this protein is that it is difficult to kill as it is able to survive heat, UV light, ionizing radiation and normal sterilization techniques1. The prion is also partially resistant to Proteinase K, a type of amino acid breakdown. This leads scientists to believe that the prion is not destroyed in the gastrointestinal tract (Campbell 2006). It is believed that the variant Creutzfeldt-Jakob disease, which is the human form of BSE, is caused by BSE. However, studies have shown a similarity between prions of BSE and TSE, but not a directly correlation to support that theory2. Symptoms of CJD are dementia, memory loss, personality changes and hallucinations. Mad Cow Disease was first found in cattle in England in 1986 and thousands of cattle died due to the disease. [[Image:BSE_001sm.jpg|thumb|300px|right|Figure 1). Brain infected by prion disease. Heavy restrictions were placed on cattle export throughout the world, with heavy restrictions occurring in Europe. The USDA implemented stringent measurzes, banning products from nations where BSE was found. Between 1985-95, it is believed that almost 1 million cattle have been infected in the UKK and about ¾ of those were fed to humans (Campbell 2006). This ban on UK beef was removed in May 2006. Recent studies have shown a link between bovine prion disease and Alzheimer’s disease.
By Kevin Pan
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Transmission of prions between similar mammalian species is efficient, whereas transmission between different species is affected by the “species-barrier”(Hagiwara et al 2013). That is it is more difficult to transfer the disease to humans, so there are longer incubation periods for the disease. It is believed that the main source of this disease in cattle originated from the food served to the cattle. Cows are naturally herbivores, so they do not rely heavily on eating meats. However, many cattle were served a protein supplement, which was a combination of meat and bone meal. This combination came from leftover food and carcasses of other animals.
There has been a decline in cases of mad cow disease recently due to a ban on feeding cattle meat and bone meat. Besides feeding surveillance, important regulations are important for containing this disease. In England, a stringent control system was implemented that prevented any animals over 30 months to be sold as human food and animal feed5. In the United States, prevention measures began in 1989 by banning import products from nations where BSE was found. In 1997, the FDA banned ruminant-based protein supplements that were being used as cattle feed6. A USDA inspector will inspect all cattle that are sent out for consumption and any cattle suspected of having BSE are sent for further testing. Due to these stringent restrictions, BSE is prevalent in less than one infected cattle per 1 million. The largest known epidemic of mad cow disease occurred in England. 177 people died after contracting variant Creutzfeldt-Jakob disease, which is believed to have been caused by eating cattle infected with BSE. In 1992 and 1993, 36,680 and 34,370 cattle died due to this disease7. In 2006, a 10 year ban on British beef was finally removed to allow for importation of British beef.