A Venatori can resist a great many illnesses and diseases. Our rapid healing ability heals nearly all damage we sustain. The deeper the wound the longer it takes. Add in silver and it can take a little longer as well.
But there are two things that are a death sentence to Venatori (and Aeternus). A were bite and a vampire bite. Both toxins destroy the antibodies in a Venatori body that fight off and heal foreign bodies etc.
The two diseases cannot exist in one host either. A human can become either a were or a vampire, but a were cannot be made vampire. The two diseases resist one another. So there are no such thing as former Venatori were’s or vampires.
However, that is also false in the case of vampires. There is a story – an old legend of Vladimir Mikhailov. Vlad was a Aeternus venatori (a hunter). He was immortal, he hunted vampires. But in Vlad’s encounters he ran across a witch. He pissed her off in the way we tend to do and she cursed him.
She cursed him to be a vampire. He did not die a normal death, his body turned on him and he lost his Aeternus immortality and abilities and turned human while his body succumbed to vampirism. This is the legend of how cursed vampires were born. Cursed Vampires procreate the same as embraced vampires with the exchange of blood. But they have no extra supernatural powers besides the basics – speed, agility and strength with all the negative side effects of becoming a vampire.
Whether or not this is the true origin of a cursed vampire. As a race we suspect there were several lines of cursed vampires created by witches over the centuries since the magic was first found. No one can really know for sure.