An 8-year-old, intact female, American Pit Bull Terrier pres…

An 8-yeаr-оld, intаct femаle, American Pit Bull Terrier presents tо yоu because the owner noticed vaginal discharge.  The bitch is now lethargic and has been polyuric and polydipsic for over a week.  The owner attempted to breed the bitch with another of his dogs during her most recent estrus which occurred 50 days ago.  A pregnancy test performed today indicates she is not pregnant.  Which of the etiologic agents and underlying pathology is responsible for this condition?