Answer: prions

AnswerCrossword Clue
prionsany of several petrels of the genus Pachyptila, located in the oceans of the Southern Hemisphere and having serrated edges on the bill
prionsPRION, a type of petrel (a small seabird (any marine bird))
prionstiny proteinaceous particle, likened to viruses and viroids, but having no genetic component, thought to be an infectious agent in bovine spongiform encephalopathy, Creutzfeldt-Jakob disease, and similar encephalopathies