Infectious agents with no genome

If the reader does not believe that viroids and satellites are distinctive, then surely prions, infectious agents composed only of protein, must impress. The question of whether infectious agents exist without genomes arose with the discovery and characterization of infectious agents associated with a group of diseases called transmissible spongiform encephalopathies (TSEs). These diseases are rare, but always fatal, neurodegenerative disorders that afflict humans and other mammals. They are characterized by long incubation periods, spongiform changes in the brain associated with loss of neurons, and the absence of host responses. TSEs are caused by infectious proteins called prions. The first TSE recognized was scrapie, so called because infected sheep tend to scrape their bodies on fences so much that they rub themselves raw. Scrapie has been recognized as a disease of European sheep for more than 250 years. It is endemic in some countries, for example, the United Kingdom, where it affects 0.5 to 1% of the sheep population each year. Sheep farmers discovered that animals from affected herds could pass the disease to a scrapie-free herd, implicating an infectious agent. Infectivity from extracts of scrapie-affected sheep brains was shown to pass through filters with pores small enough to retain everything but viruses. As early as 1966, scrapie infectivity was shown to be considerably more resistant than that of most viruses to ultraviolet (UV) and ionizing radiation. Other T...
Source: virology blog - Category: Virology Authors: Tags: Basic virology Information bovine spongiform encephalopathy cervid wasting disease Creutzfeldt-Jakob disease Fatal familial insomnia mad cow disease prion scrapie Stanley Prusiner transmissible spongiform encephalopathy TSE viral Source Type: blogs