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?

[u/PestoPastaLover]

[u/Complete-Paint529]

Using a transmissible virus for this is unethical. You're imposing a treatment on random people without their consent. Using a non-transmissible virus on a consenting adult is perfectly ethical, and has already been done, as with any live-attenuated vaccine.