In 1996, while I was traveling in South Sudan, I visited a small hospital in Tambura. People there were sick in all sorts of ways–with malaria, sleeping sickness, and other illnesses–but one group of patients left an impression on me that I’ll never get rid of. They all stayed in a single, small narrow building. They lay on two rows of clean, thin mats on the floor. They were all clothed and were supremely bored. The men kept one pant leg rolled up to the knee. Exactly what sort of disease a sick person has can be mysterious–Is it stomach cancer? Is it HIV? It is mumps?–but there was no confusion in this room. All the patients had a short stick attached to their legs, seemingly tied by a string. That string was, in fact, an animal.
Its official name is Dracunculus medinensis. It’s commonly known the guinea worm. Measuring up to four feet long, the worms were lodged in the connective tissue inside the legs of the Tambura patients, their head poking out of a blister. The only way to get rid of the guinea worms was to wind them onto sticks, which nurses then twisted, slowly and steadily, for two weeks.
Seventeen years later, the guinea worm’s days are now numbered. In 1986, 3.5 million people suffered from guinea worm infections across Asia and Africa. In 2012, there were only 542 cases in the entire world. The vast majority of those cases–521–occurred in South Sudan. But that’s a huge improvement: in 2008, South Sudan had 3,618 cases. From 2011 to 2012, the number of guinea worm infections there dropped by 49%. If public health workers can keep up that pace, the World Health Organization expects the guinea worm to be eradicated in the next few years.
Newspapers keep an inventory of obituaries for famous people who are in their golden years, with only the date and cause of their death left to fill in when they finally pass away. The recent news about the guinea worm’s impending extinction prompted me to write an obituary for it. I will not miss it as a disease, but as an animal, it will leave a mind-boggling absence.
The guinea worms have wound themselves around human history for thousands of years. Egyptian mummies contained them. The Book of Numbers describes how the Israelites were stricken by “fiery serpents” as they wandered the desert–they, too, are believed to be guinea worms. Muslim pilgrims on the hajj suffered from guinea worm infections on their way to Medina, which led to its Latin name, which means “Little Dragon of Medina.” Greek and Persian doctors were winding the worms on sticks over two thousand years ago. It’s possible that the symbol of medicine–snakes coiled around a staff–maybe actually represent this ancient treatment.
For centuries, no one could say how guinea worms could grow inside human bodies. Some thought they spontaneously appeared. Their true nature was uncovered by the Russian naturalist Aleksej Fedchenko in the 1860s. In his early twenties, Fedchenko traveled widely in Central Asia. “Upon returning to Samarkand from a trip across the plain,” he wrote in an 1870 monograph, “I learned that the native doctor, a specialist in extracting guinea worms, already had had the occasion of removing several parasites from persons arriving in Samarkand from Bukhara.”
Fedchenko was delighted. He had studied parasitic worms as a student, and now he could do some original research. Every morning, the doctor would bring a bottle of worms to Fedchenko, who would spend all day peering at them through a microscope, making detailed drawings. One day he noticed that there were water fleas in the water. He plucked out the poppy-seed-sized animals and put them under his microscope, too. “I saw in each one several familiar looking embryos of the guinea worm,” he wrote.
Fedchenko died in 1873 in a mountain climbing accident at age 29. It was left to parasitologists who came after him to work out the bizarre life cycle of the guinea worm. The worms are born live and will squirm through fresh water for days, waiting for a water flea to notice their quick, jerky movements. For water fleas, it seems like an easy hunt, but the joke’s on them. Instead of getting a meal, they become a nursery. The guinea worm embryos drill their way out of the water flea’s digestive tract and swim around in their body cavity, feeding on the ovaries or testes of their host. Over the next few weeks, they molt twice, growing to larger stages. But the parasites will die as embryos unless the water fleas get inside of humans.
This leg of the journey occurs when a person drinks unfiltered water from a pond. The water flea plummets into the stomach, where it is dissolved by digestive juices. The guinea worm embryo, on the other hand, swims onward into the intestines and then drills its way out, crawling into the abdominal blood vessels and finally reaching the abdominal muscles over a couple weeks.
Of all the many remarkable things about the guinea worm, here is something particularly remarkable: this journey causes its victim no pain. It’s not a fleeting infection, either. It takes the guinea worms three to four months to become sexually mature. The males only get to be 4 centimeters long; the females reach 25 times that length. Most of that extra space in their bodies is taken up by their uterus. If people have both males and females in their body, they can find each other and mate. After this internal congress, the male guinea worm creeps off to some corner of the body and dies. The female, meanwhile, swells with progeny. Three million embryos begin to grow inside her.
It takes months for the multitudes she contains to grow to the point when they’re ready to leave their mother–and their human world. She begins her journey to ground, slithering through the connective tissue until she reaches her host’s leg and creeping down further towards the foot. Only now, over a year after taking in the guinea worms, does a person become aware of what’s been happening. The guinea worm mother pierces the skin from the inside and releases an irritant that creates a painful blister–“burning without cease” as one tropical disease expert once put it.
There is only one balm for this pain: water. When people splash water on the blister, the guinea worm responds by twisting into a contraction and vomiting embryos from her mouth. The pain subsides for a while, but the blister swells again until another splash of water delivers another batch of guinea worm babies. The pain lasts, off and on, for months–until the parasite’s entire uterus has emptied its millions of embryos. Some of them may be lucky enough to end up in a pond full of hungry water fleas, where they can continue the cycle.
Guinea worm infections can be fatal, but only due to human impatience. People sometimes try to yank the worm out from its blister, whereupon it retreats into the body, where it triggers an intense immune response that swells the leg. The worm dies and becomes a site for dangerous bacteria infections. Worms can also die during their journeys inside the body, and their calcified remains can cause crippling arthritis. Even in the best outcome, when the worm can be wound out of the body, the intense pain can linger for several more months. In the 1970s, doctors working in rural India would come across villages where just about every resident was bedridden, waiting to be rid of the guinea worm. For poor farmers, the infections could be economically devastating, keeping them out of their fields for months.
No one has ever invented a vaccine for guinea worms. There is no reliable drug to treat an infection. Modern medicine hasn’t gotten much better than sticking winding–the treatment that worked thousands of years ago. And yet doctors have recognized since the 1930s that the guinea worm had a rare distinction: it could potentially be eliminated from the face of the Earth. Unlike many other pathogens, guinea worms are pretty easy to track, and their life cycle’s pretty easy to block. If they can’t get into water fleas, they’re finished. And even if they do take that step, they still need to get into humans.
Some individual countries managed to eradicate guinea worm within their borders, and in 1986, the Carter Center backed an international effort to wipe them out altogether. In 21 different countries, public health workers identified the ponds where guinea worms were lurking and sprayed them with insecticide. They handed out filters for drinking water. They kept infected people away from water, so as not to allow the worms to launch a new generation. The campaign enjoyed a slow but steady success. Country after country declared itself parasite free. By the early 1990s, experts were predicting eradication within a few years. They had to keep pushing that date a few years into the future, however. The campaign turned out to be more expensive than had been expected. Poor organization in some countries stalled progress. South Sudan proved particularly difficult thanks to a long civil war. Now that South Sudan is its own country, the guinea worm campaign is moving full tilt.
The guinea worm is now one of the most endangered species on Earth. There is no hidden population of the parasites lurking in dogs or raccoons, waiting to launch a renewed attack. Those animals get infected with their own species of Dracunculus, but cannot host our little dragon. Every guinea worm still alive today had to be spewed out of a loving mother dwelling in a human body. If they do continue to become rarer and disappear, it will be only the second time in history that we eradicated a human disease, the first being smallpox.
We may still need to kick the guinea worm’s date with oblivion a few more years down the road, however. While South Sudan is now relatively peaceful, Mali has erupted into civil war and Al Quaeda-linked rebels have taken over the northern portion of the country. In the New York Times last week, Donald McNeil reported that public health teams haven’t been able to remove the worms and teach children how to avoid infection in the rebel-held territory. Officially, only seven cases of guinea worm were recorded in Mali last year, but there could be many more that have gone unrecorded. And thanks to the millions of embryos each guinea worm produces, it takes just one person to spark a massive outbreak. In 2006, McNeil writes, an infected student walked 250 miles to the northern Kidal region of Mali, where he spread the parasites to at least 400 other people. We can only hope that the civil war will end in Mali soon–not just to stop the immediate loss of life, but also to allow public health workers to stop the enormous suffering caused by diseases like guinea worms.
If we do drive Dracunculus medinensis extinct in the next few years, we will have eliminated a disease that was once spectacularly widespread. But we will also be wiping out a remarkable creature about which we actually know very little. When I went hunting for new research on the natural history of guinea worms this week, I found just about none. Most of what scientists have discovered about guinea worms, they discovered long ago. No one has sequenced the guinea worm genome. No one has used new staining technology to make its neurons light up. We don’t know how long it has infected humans, or where it came from before that. What little we do know should make us intensely curious about what we don’t know–and what we may never know.
For example, in 2002, a team of scientists at the State University of New York discovered that guinea worms make morphine. They speculate that it may use the drug to ensure a peaceful life inside its human host. The morphine may numb its host’s pain sensors, so that it can lurk unnoticed. Morphine also suppresses the immune system, which may partly explain how it is that we can carry a four-foot-long worm inside of us for over a year without experiencing organ rejection. Just as transplant surgeons tamp down a patient’s immune system before putting in a new liver, the guinea worm may apply its own immune-suppressing pharmaceuticals.
That’s just speculation, however, and once scientists can no longer study living guinea worms, it will probably remain so. And so will all the other secrets that the guinea worm is about to take to its grave.
(For more on guinea worms and parasites that don’t face imminent extinction, see my book Parasite Rex.)
Originally published January 24, 2013. Copyright 2013 Carl Zimmer.