It is circa 500 BC, and Hippocrates records rare but localised outbreaks of madness within livestock; he observes that the animals’ neurological capabilities rapidly decline after years of apparent normality. When he investigates, he finds that the brains of these animals are ‘very full of dropsy and of an evil odour’. He hypothesises that this disease would be able to spread and infect humans too (McAlister, 2005). To him, this is obviously not a product of Gods like the common ideas of infection at the time, instead he describes it as ‘organic’.
It is 1755, farmers in Britain watch their sheep go into hysteria, rubbing their hind-quarters against fenceposts and rocks until they …show more content…
Not only this, but the prion proteins are resistant to proteases since they are undefined and take many forms. This is because of the possibilities of folding, meaning proteins can take many different shapes; these different conformations are known as strains. Not only this, but the prions stick to metals and plastics while retaining infectivity (Weussmann, 2002). This means no inoculation for these diseases can be developed with our current methods. The resistance of prions was shown in 1946, when sheep were vaccinated with a virus that had be inactivated with heat. The sample contained scrapie PrP, and the entire flock was infected with Scrapie (Vallabh S, 2013).
Since the proteins form fibres, there are two places of conversion, meaning prion proteins are replicated rapidly; however, they have a long incubation period, so a prion disease can go years before any symptoms occur (CDC, 2015).
Prion proteins are believed to originated from a messenger protein, a pathogen that lost its genetic material to the surrounding cell, or from a proteins’ urge to form beta-pleated sheets (Weussmann, 2002).
There are many diseases that prions are believed to cause, both in humans and in animals. The following are known:
• Scrapie (in sheep and …show more content…
They are thought to be caused by prions or spiroplasma (a group of bacteria without cell walls) (Various, 2016).
The ‘spongey’ nature of neural tissue sometimes caused by the expansion of vacuoles in the neurons of the brain (known as vacuolation). The dead neuron (caused by the prions) alert lysosomes to clear up, however these lysosomes burst and kill other neurons (Cobb, 2009). The harmful Prion proteins gather at the synapses of neurones, stopping them functioning; however the ‘spongey’ changes occur in cisternae of the smooth endoplasmic reticulum, between the axons of neurones, and glial cell processes (Soto, 2011).
As you can see in the image above, there is a lot of shrinkage in the brain, and it is a lot less dense; the loss of neural tissue indicates a transmissible spongiform