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Do you know some examples of virus or a viroid (or a prion) that originated from a known living organism? How does the virus/viroid/prion lives? Does it paratize the organism from which the virus originated?


Thanks to the first answers I have examples of newly originated prions. Does someone know such an example about viruses?

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Retrograde evolution is not an impossible concept, I know examples of unicellular parasites (in a way) evolving from multicellular lifeforms (See Devil Facial Tumor Disease and Canine Transmissible Venereal Tumor). A related question would be: how ancient the viruses are. Retrograde evolution of a eukaryotic cell to a virus would be a huge evolutionary jump. – WYSIWYG Nov 4 '13 at 11:30
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Prion diseases are still very poorly understood, but one of the dominant theories is that they are misfolded proteins that cause disease by catalyzing the misfolding of more proteins of the same type. If that is the case, then they arise from the organism that they affect simply by protein misfolding. In the case of bovine spongiform encephalopathy (mad cow disease) being transmitted to humans and resulting in new variant Creutzfeldt-Jakob disease, it seems like it might be transmissible between species, but it probably needs to infect a closely related species so that the protein has a homolog it can act upon.

Can't say I know of any examples where people have shown the de novo creation of a virus from a living organism. There are definitely virus protein homologs in the genomes of organisms, but directionality is hard to argue since its common for viruses to pick up host genes, or leave behind viruses genes.

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Prion diseases arise spontaneously fairly often. There are only ~170 total cases of human infection by mad cow disease, but there are ~50 cases/year of Creutzfeldt-Jakob disease, which is a spontaneous strain of prion diseases in humans. There is a strong case that Alzheimer's and Parkinson's diseases (among others) are similar in nature, in which case it's a much more frequent occurrence.

However, they are the consequence of a misfolding and aggregation of a naturally occurring protein produced in our brains. In this sense, they are nothing like the complexity required to produce a de novo virus. The closest viral analogy would be retroviruses, which could insert their genome into your DNA, die off, and then possibly spontaneously revive at a later date.

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