Hello, I'm looking for a particular story, it is a rather old story and it may not be on this site

the story is about a boy, who is picked up in a van and taken to facility and forsably transformed by the scientist who is working to weponice the transformation process,

the process is question is a sentient panties, genetically created by the scientist in question which turn the boy into a girl, the pants, transform the host into a breading ground for new pants (there alive) and to feed off, they do this by injecting the host with a retro-virus to re-write the host DNA and take control of the host nerves system to partly control them