![]() ![]() PrP sc is folded abnormally, and the resulting conformation (shape) is directly responsible for the lesions seen in the brains of infected cattle. This leads to an exponential increase of the PrP sc protein, which aggregates. Once introduced into the body, the PrP sc contained within the prion binds to PrP c and converts it to PrP sc. PrP exists in two forms, PrP c, the normal form of the protein, and PrP sc, the infectious form. ![]() It is this variant that constitutes the prion particle. The cause of spongiform encephalopathies, such as kuru and BSE, is an infectious structural variant of a normal cellular protein called PrP (prion protein). Al Jenny, USDA APHIS scale-bar data from Matt Russell) (b) This prion-infected brain tissue, visualized using light microscopy, shows the vacuoles that give it a spongy texture, typical of transmissible spongiform encephalopathies. PrP sc may arise spontaneously in brain tissue, especially if a mutant form of the protein is present, or it may occur via the spread of misfolded prions consumed in food into brain tissue. (PrP sc) when it encounters this variant form of the protein. The disease can be spread from human to human by blood, so many countries have banned blood donation from regions associated with BSE.įigure 1. BSE still exists in various areas, and although a rare disease, CJD is difficult to treat. Later on in the outbreak, however, it was shown that a similar encephalopathy in humans known as variant Creutzfeldt-Jakob disease (CJD) could be acquired from eating beef from animals with BSE, sparking bans by various countries on the importation of British beef and causing considerable economic damage to the British beef industry (Figure 1). Cattle dying of the disease were shown to have developed lesions or “holes” in the brain, causing the brain tissue to resemble a sponge. On the other hand, BSE was initially thought to only affect cattle. Kuru was controlled by inducing the population to abandon its ritualistic cannibalism. Individuals with kuru and BSE show symptoms of loss of motor control and unusual behaviors, such as uncontrolled bursts of laughter with kuru, followed by death. BSE, originally detected in the United Kingdom, was spread between cattle by the practice of including cattle nervous tissue in feed for other cattle. ![]() ![]() Kuru, native to humans in Papua New Guinea, was spread from human to human via ritualistic cannibalism. The disease was spread by the consumption of meat, nervous tissue, or internal organs between members of the same species. Historically, the idea of an infectious agent that did not use nucleic acids was considered impossible, but pioneering work by Nobel Prize-winning biologist Stanley Prusiner has convinced the majority of biologists that such agents do indeed exist.įatal neurodegenerative diseases, such as kuru in humans and bovine spongiform encephalopathy (BSE) in cattle (commonly known as “mad cow disease”), were shown to be transmitted by prions. Prions, so-called because they are proteinaceous, are infectious particles-smaller than viruses-that contain no nucleic acids (neither DNA nor RNA). Define viroids and their targets of infection.Describe prions and their basic properties. ![]()
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