An agent that is smaller than a virus causes scrapie. It is either a protein called a prion or it is another substance closely associated with the prion protein. Scientists still have a lot to learn about the scrapie agent and exactly how it works.
Tissue valves are made with tissues from porcine (pig) heart valves or bovine (cow) cardiac tissue because they function like human heart valves. Once the tissue is removed from the animal, it is chemically treated to preserve the tissue and prevent immulogic reactions once it is placed in a patient.
Still, most tissue valves, including porcine valves, are not as durable as the mechanical valve replacements which are made substances including titanium, Teflon and steel. Obviously, this is one of the downsides of porcine valves as porcine valve leaflets tend to calcify and degenerate.This can lead to a collapsed pig valve in the human heart. However, some recent studies are beginning to challenge that adverse effect of pig valves.till, most tissue valves, including porcine valves, are not as durable as the mechanical valve replacements which are made substances including titanium, Teflon and steel. Obviously, this is one of the downsides of porcine valves as porcine valve leaflets tend to calcify and degenerate.