Prions, also known as prions, are host-encoded, conformationally abnormal proteins that are nucleic acid-free, self-replicating, and infectious. Prions are nucleic acid-free, protein-based infectious agents that can only survive inside the cells of their hosts. Prions are a class of hydrophobic proteins that can infect animals and are not immunogenic in host cells. Prion proteins include both cellular and pruritic types. Prions are capable of causing spongiform encephalopathy in animals, including cattle, sheep, and humans, commonly known as “mad cow disease”. Clinical manifestations of prion infection include ataxia, myasthenia gravis, dementia and other neurologic manifestations. There is no effective treatment for prion infection, but the main focus is on prevention, elimination of infected animals and isolation of patients.