Any observer of guinea worm disease, or dracunculiasis, will tell you that this waterborne parasitic disease should be simple to eradicate. After all, no vaccinations or costly drugs are needed, the disease cannot be passed from one person to another, and the wounds that the worm itself causes on a patient’s body are handled effectively with what you would use for a scraped knee: clean water, antiseptic, gauze, and an antibacterial ointment.

But eradication of the nematode, Dracunculus medinensis, requires that most slippery of ingredients: a change in human behaviour. In fact it requires two changes, one of which is particularly difficult to effect because of the parasite’s wily ways.

The life cycle of the worm begins when a person drinks water infected with its larvae (see box). So the first change that health campaigners are pursuing is to persuade people to filter their water before drinking it.

Then over the course of a year the larvae mature and grow into long, spaghetti-like white worms that live in the body’s subcutaneous and intramuscular tissues. When the female worms are ready to emerge and lay their eggs, they ingeniously cause such blistering of the skin and such a fiery pain that the host naturally seeks out cool water for relief, thus enabling the worm to lay its eggs in water and continue its life cycle.