AutoCAD 2013 :: Drawings Overrun With Unused Line Types

We've having an office wide problem of drawings getting bogged down with, in some cases, hundreds of linetypes. Not sure where the source of the problem is coming from but as we contiunally use the drawings they keep gaining more and more linetypes, like a snowball rolling down a hill, and the files become so large they are almost unusable. The linetypes don't purge out of the drawing and are not connected to anything. I've tried everything I can think of to clear out the linetypes and the only thing that seems to work is wblocking them. Which when we're talking about hundreds of projects consisting of hundreds of files is a lot of work. We do wblock the drawings in a project on occasion to keep the files usable but they just become infected again eventually.

What might work to clean them up on a batch basis? I've attached a file that's infected so you can take a look. This is a file that has never had anything xref'd into it and was created as a brand new file when originally created. At some point over the last 3 weeks it got infected with the linetype disease.