Prions – novel infectious agents
differing from all other known pathogenic agents

Prions are simple proteins that are much smaller than viruses. They are unique since they lack a genome. All other known infectious agents contain genetic material.
Bacteria are often surrounded by a strong protective cell wall and replicate through simple cell division. Fungi may cause infections of the mouth, throat, lungs, and skin. Parasites thrive on their host, often causing longlasting chronic infections. Viruses are small packages of genetic material that can only replicate inside a cell.

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