Back in Leviticus, for people that gripe about all God's laws, are laws regarding cleanliness, and health. Of course the people at the time didn't understand that these laws had to do with disease prevention, it took a while for science to catch up and realize that these laws cut down on the spread of infectious diseases.
If a person doesn't want to have health, and they want to engage in things that destroy the immune system, a person can't say they were not warned. Did God cause it? No. It was not God that destroyed perfection and brought death into the world, it was man.