The story goes that the Israelites complained one time too many on the exodus, and God sent fiery serpents to besiege them. When the Israelite's were bitten they got sick and died. When the people repented, they went to Moses and begged him to get God to remove the snakes. Moses prayed, but God did not remove the snakes, choosing instead to effect healing to those who were bitten. The most common explanation of the event is that it was through the Israelite's faith in God that they lived after being bitten.
Guinea worms are parasitical and enter the body through contaminated water.
The female burrows her reproductive organs towards the surface of the skin and causes an ulcer or abscess. When that portion of the skin gets wet, the worm protrudes her organs and releases thousands of embryos. On the other hand, there were no serious aftereffects if the worm was removed successfully. The bronze serpent on a stick, therefore, was made to teach and remind the infected Israelites to wind the worm around a stick slowly and patiently. If they did so, they would live.