of course Susan, anything COULD happen, but what happens is another story.
Like most animals, if monitors are kept in conditions foreign to them, they lose their immune system and die from ANYTHING. Respitory infections and mouthrot are causes by common bacteria thats everywhere, etc etc etc.
They animals are designed to live in dirt. I would imagine they have strong defenses against such things as you mentioned.
I would not worry about tetanus, or any common bacteria. I would worry about making sure your monitor is strong and healthy.
The real actual truth is, once they are strong and healthy, they are so very very hard to kill. They are kinda like flatworms, cut them in pieces and more monitors will grow out of the pieces. OK, thats a lie, but they are indeed incredibly strong and hard to kill.
The point is, GET THEM STRONG. Cheers