There is absolute proof that evil spirits or demons bring disease and sickness upon people. All medical doctors find baffling cases which cannot be explained medically.
                 Job 2:7,  So went satan forth from the presence of the Lord and smote Job with sore boils from the sole of his foot unto his crown.

                      Satan caused these terrible sores to be upon Job's body. No medicine of any kind could heal him. Job had no physical disability and no organ malfunction. It was a direct work of the devil. God became Job's physician and healer.
            Job 42:10, And the Lord turned the captivity of Job, when he prayed for his friends: also the Lord gave Job twice as much as he had before.