[evan_au (OP)]

It appears that the Cholera bacteria Vibrio cholerae does not actually cause the symptoms of Cholera until the bacterium is infected by a virus (a bacteriophage), which carries the gene for Cholera toxin.

• Could we inoculate people against Cholera by giving them a dose of uninfected Vibrio cholerae?
• Could we cure the human disease Cholera by curing the Cholera bacterium of its disease?
• See: http://en.wikipedia.org/wiki/Vibrio_cholerae#Genome

[CliffordK]

It may well be effective, and might give longer lasting protection than the current vaccines.  But it certainly would need a lot of testing.  It could be very bad if more people ended up being colonized by the virus free cholera, then contracted the pathogenic version.

I wonder if phages would be a factor in other diseases. 

[cheryl j]

Diptheria only produces the diptheria toxin when it's infected with a phage. There are probably others.