Describe a beneficial use for a microbe in treating disease. These answers

 
Describe a beneficial use for a microbe in treating disease. These answers can vary and may be experimental. Use some outside library resources like CINAHL Plus with Full Text or NCBI.gov to find these unique viral applications. Entries should include an overview of the viral application and the benefit to patient health or society.
Also, include any complications with this strategy preventing its immediate application.