The rod of the Greek god Asclepius, entwined by a serpent, is a symbol of medicine, often confused with Hermes staff (the caduceus). Asclepius was the god of healing and medicine. The symbol has a supposed hidden meaning associated with the Dracunculus medinensis, parasitic nematode that uses the human as a host.
The worm is ingested through a contaminated water source, the copepods die and release D. medinensis larvae which penetrate the stomach and intestinal wall. They mature in the abdomen for up to a year upon which the fertilized female migrates to the skin, often the lower extremity, and induces a painful blister to form, enticing the human host to dip their burning skin into water to alleviate the pain. The blister then bursts and reproductive larvae pour out into the water and await the next host that comes their way.
The worms can reach a meter in length however they cannot be removed by pulling off their protruding head – the worm may break and induce an anaphylactic response leading to death of the human host.
Thus in antiquity the worms were removed slowly, over a period of weeks, by winding the worm on a stick by a few cm per day. Historians say that physicians may have promoted this type of healing by displaying a sign of a worm on a rod. So that mighty snake of medicine might in fact have originally been a pesky worm.