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.
A donor valve can be expected to last 10-20 years. Tissue Valve (sometimes called âbioprostheticâ valves) Tissue valves are created from animal donorsâ valves or other animal tissue that's strong and flexible. Tissue valves can last 10-20 years, and usually don't require the long-term use of medication. For a young person with a tissue valve replacement, the need for additional surgery or another valve replacement later in life is highly likely.