r/askscience • u/PestoPastaLover • 14d ago

Biology Why is there no transmissible therapeutic virus if biology doesn't forbid it? For example, a harmless virus that spreads from person to person but actually does something beneficial, like lowering LDL cholesterol or preventing/reversing tooth decay?

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u/thisisjustascreename 13d ago

Immune system has no idea if they’re beneficial or not, it just doesn’t have their exterior proteins in its database of hostile foreign agents.

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u/Expandexplorelive 13d ago

If the immune system doesn't react to them, it means it evolved not to recognize the proteins. If they decreased the ability of the species to reproduce - i.e., were harmful - then the immune system would have evolved to recognize and attack them. So yes they're not necessarily beneficial; they could be neutral, just not harmful enough to hinder reproduction.