The number of human cases of guinea worm, a painful and debilitating tropical illness, fell to a record low of just 10 last year, according to the Carter Centre, the foundation set up by the late former US president Jimmy Carter. But despite years-long declines, it remains almost impossible to completely eradicate the parasite. Only one human illness has been entirely eradicated: smallpox. Why is it so difficult, and could guinea worm one day be the second? Ian Sample hears from co-host Madeleine Finlay, and David Molyneux, emeritus professor of tropical disease microbiology at the Liverpool School of Tropical Medicine. Help support our independent journalism at <a href="https://www.theguardian.com/sciencepod">theguardian.com/sciencepod</a>