Protein-like infectious organizations (agents). They consist of cellular proteins (PrPc) that are transformed into an infectious, abnormal isoform (PrPSc). After long incubation periods (years), so-called transmissible encephalopathies (TSEs) may occur known under different names (BSE = bovine spongious encephalopathy in cattle, Scrapie in sheep, Creutzfeldt-Jakob disease in man). Transmission occurs by feeding undercooked (below 141 °C) nerve/brain portions of infected animals or by eating contents of flies that had fed on such material (experimentally proven in scrapie infections by Post et al. 1999). It was shown there that all hamsters being fed with larvae and/or adult flies (Sarcophaga carnaria) showed full symptoms of scrapie. This proves that there is existing a vital cycle in nature, where apparently at all times such prions are present, which, however, only in rare cases introduce severe (deadly) symptoms.