Puppy vaginitis (also called juvenile vaginitis) is inflammation of the vagina in a puppy that has not reached puberty. In contrast, adult-onset vaginitis affects some spayed female dogs. The cause of either form of vaginitis is not well understood but it is usually a mild condition that is easily treatable. Vaginitis and pyometra are medical conditions that only occur in females. Vaginitis is an inflammation of a dog's vagina, the female reproductive passage that.