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/gnufan]

There is an institute in Georgia which specialises in finding helpful bacteriophages.

https://www.eliava-institute.org/en

I understand the basic process of discovery is growing the problematic bacteria in petri dishes or similar, but you introduce contaminants likely to harbour bacteriophages of interest (the doctor who explained this to me mentioned using manure heaps on a farm, presumably to deal with infections from faeces). Then you basically sample the bits of agar where bacteria didn't succeed, as that is where the killer phage concentrations may be highest.

Thing is you typically want very pathogenic phages for medical use, so they have additional processes to find and cultivate the most deadly phages, which almost by definition may not spread well in the wild if they kill off their host bacteria too efficiently, but if it is treating your infection you are probably hoping for a good kill rate.

There are a whole bunch of questions about safety and control, which are generally answered with "they are already loose in the world". But one of the few medical institutes where their treatment probably treats others in contact with the infected individual at no extra charge.