See if this passes muster with contemporaneous religious authorities:
Disease comes from tiny invisible creatures, as part of a punishment from a deity/evil spirit/what have you...
Problem solved?
“Problem solved?”
Probably! Ha ha good. As long as the local priests don’t think you have a method to avoid the punishment!
Once it comes as punishment from a deity they no longer have reason to try to prevent it or cure it. That’s fighting against God’s will, which makes you next.