Lurking within the streams and lakes of sub-Saharan Africa is a parasite that has a particularly nasty way of leaving the human body. If you drink unfiltered water where the parasite resides, it makes its way into your abdomen and sets up shop. Once it is ready to leave, it heads for a foot – ready to depart in a gross, but awesome way.
Dracunculiasis medinensis, this is your life.
D. medinensis, or the Guinea worm, is a parasitic nematode that is of the same order as several other human parasitic worms, including those that cause river blindness and elephantiasis. It’s life cycle begins in fresh water, where it infects tiny crustaceans known as water fleas and moults inside them. Once the worm larvae has moulted twice, it becomes infective and if a human drinks unfiltered water containing the water flea-worm larvae cocktail, they become infected.
Once the unfiltered water reaches the stomach, acids kill and dissolve the water fleas away, leaving only the Guinea worm. The worm then wriggles out through the stomach wall into the intestinal cavity and sets up shop there, waiting for a mate. At this point, the host has no idea that they’ve been infected.
The male and female larvae mature over the next two to three months and mate, which kills the male worm. The fertilized female continues to grow – sometimes as large as one metre in length – over the next year, slowly migrating through the body. More often than not, this migration occurs downward – the female moves towards the legs and feet.
Now, the host is aware of the infection because the fertilized female causes a burning sensation and a blister begins to form from which the Guinea worm can exit.
The worm doesn’t actually burn a hole through the skin like some sort of wiggling flamethrower, but it causes the blister to rupture, allowing the female to emerge and expel larvae.
The Guinea worm is ‘clever’ though – it doesn’t have any mind-control techniques but to successfully reproduce, it wants to expel the larvae back into a body of water to start the life cycle again.
Causing a ‘burning sensation’ as it tries to exit means that infected human hosts want to dip their feet and legs back into the water to soothe their sore skin.
And so the life cycle continues.
There is no vaccination or treatment regime to prevent the disease. Instead, it’s necessary to provide safe, filtered drinking water to communities which will prevent the infection from occurring in the first place.
For infected individuals, treatment requires a small stick to be placed near the blister where the Guinea worm makes its exit. Over the course of a few days to a couple of weeks, the stick is slowly turned and the worm wraps itself around it, slowly being pulled out. Once the worm has left the body, it no longer poses any danger – but it does not provide immunity. Drinking unsafe water will cause the cycle to begin anew.
The Rod of Asclepius, which sees a serpent entwined around a staff, is often associated with medicine and health care in the modern era. There are some theories that suggest this image has come to be associated with the Guinea worm because of the way it is removed from the body.
Since 1986, human efforts to eradicate the disease have been highly effective. The Carter Center, in the US, began leading the campaign in that year when some 3.5 million people had been infected. In the 30 years since, the number has been reduced to just 25 reported cases in 2016.
It is on the verge of eradication and will likely become the first parasitic disease of humans to see total global annihilation.
Will we feel bad about about sending another species extinct? Will we mourn the Guinea worm?
I wouldn’t say so.