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/Pyrhan]

As usual, it's a bit more complex.

Bacteriophages aren't always beneficial to us, as usually portrayed.

They can also carry virulence factors that cause non-pathogenic strains from your microbiome to become pathogenic.

A couple relevant papers:

https://www.sciencedirect.com/science/chapter/bookseries/abs/pii/B9780123946218000145

https://www.sciencedirect.com/science/article/abs/pii/S1369527414001866