Have you ever heard of proteins, which cause fatal and transmissible neurodegenerative diseases for both people and animals? Did you know that these misfolded proteins are called Prions, and they can increase their numbers by using the functions of living cells (in this respect, prions are similar to viruses)? Even though prions had been found out almost 40 years ago by Stanley B. Prusiner, much is still left to be understood about the prion, including how exactly it replicates and causes other proteins to fold and the origin of the deadly molecule itself. Furthermore, most pressingly, how to treat or cure any of the numbers of terminal diseases it causes in animals and humans. In this book, you will discover the historical background of prions, their importance, structures, and the most known human prion diseases, the Public Health System's most significant challenges, and the future directions for the study of prions. All of that put in one book for a more detailed study of the still unexplored topic of deadly proteins - prions.