A man receives a box containing a desiccated hand with a large ring on it's finger.
While wrestling the ring off the hand disintegrates into dust which he inhales and is infected with lycanthropy.

He starts attacking prostitutes, one of which escapes with only minor injuries and also becomes a werewolf.

The cops investigating the attacks kill the two werewolves and at the end are informed that those infected by this virus who die will come back as vampires

I read it from the local library as a paperback in the mid 90's

Can't remember title or author