Thank you for the question about diseases, “What does the Bible say causes disease?”
As one reads Genesis 3, there are two primary causes of diseases. Those two causes are from the ground being cursed by God and the seed of death in humans. Can this be the beginning of mutations of DNA/RNA’s that allows for mutation of cells to become “diseases”?
Genesis 3 says this, “17 To Adam he said, “Because you listened to your wife and ate fruit from the tree about which I commanded you, ‘You must not eat from it,’ “Cursed is the ground because of you; through painful toil you will eat food from it all the days of your life. 18 It will produce thorns and thistles for you, and you will eat the plants of the field. 19 By the sweat of your brow you will eat your food until you return to the ground, since from it you were taken; for dust you are and to dust you will return” (A searchable online Bible in over 150 versions and 50 languages).
Although the Scriptures do not declare how Adam/Eve and their descendants will physically die, it appears that their physical body will deteriorate by hard labor and by the food that they consume. With thorns and thistles rising, the nutrients of the soil and the genetics of plants began to change. As animals eats the fields, that will have an adverse affect on them. With humans consuming animals and plants, there is the deterioration of body cells. Those are the primary causes for diseases.
This became further complicated with the Flood. Climate change on earth due to rain and solar radiation upon earth. The protective shield of water and the changing of the earth’s temperature affected all life forms on earth. With human’s actions of abuse and misuse of the earth’s resources contributed to the imbalance of life on earth. Death was foreign on the earth before the Fall of Adam and Eve. After the Fall and the Flood, life drastically change as humans abused each other, animal and plant life. It may well be that humans accelerated the mutations by their actions that brought disease and death on earth.
It may well be that the Scriptures speaks of a New Heaven an a New Earth whereby God will restore what humans have marred above the earth, on the earth, and in the waters of the earth.
SUMMARY: The primary cause for diseases is linked to human’s abuse and misuse of earth’s natural resources. God created man to care for the earth and instead he has carelessly misused its resources for one’s selfish pleasure and domination of others.
For more perspectives:
https://www.quora.com/What-does-the-Bible-say-causes-disease