The Rise and Fall of the Guinea Worm, Dracunculus medinensis

As of May 2013 there's a bounty on the Guinea worm (Dracunculus medinensis) in Nigeria. Anyone reporting a confirmed case of Guinea worm infection, or dracunculiasis, will receive a cash reward of N25,000, or about US158.00. This marks another milestone in the battle of humanity versus the Guinea worm that's been going on for thousands of years.

Even today, the only effective way to get rid
of a Guinea worm is to slowly wind it around a
stick. The process can take weeks.
 Public Health Image Library.

Fortunately for anyone hoping to claim the cash, a case of Guinea worm infection is fairly easy to recognize. A description from Persian physician Avicenna, written a thousand years ago, is as good as any we'd write today:
“A pustula first appears and swells up, but afterwards contracts down again to a mere bleb. ...the bleb perforates and dark red matter is continuously exuded. ...movement can be distinguished beneath the skin as though some living thing were there, and indeed... a worm is present... For the most part it is the legs that are involved...” (translation quoted in Hoeppli, Parasites and Parasitic Infections in Early Medicine and Science).

The Origin and Historic Range of the Guinea Worm

Guinea worm may be gone from Nigeria, and the bounty is part of an effort to prove that. In the last quarter century the parasite has been pushed back, and back, and back, to its last bridgehead in Sub-Saharan Africa north of the equator.

As recently as 80 years ago, however, the worm was a torment in present day Uzbekistan, Turkmenistan, Pakistan and India, throughout the Arabian Peninsula, and in much of the northern half of the African continent. In its heyday, about 120 million people lived in its range and were at risk of infection. More than three million people suffered this extremely painful, debilitating, and basically untreatable parasitic infection every year.

When Did the Guinea Worm First Infect Humans?

We don't know where the Guinea worm first infected a human. It's tempting to think that it evolved somewhere in Africa because similar parasites of other vertebrates occur in both the Americas and Australia, both of which, with Africa, were part of the supercontinent Gondwana 100 – 125 million years ago.

Whatever its origins, the earliest written records of dracunculiasis come from North Africa and the Middle East, with the area around the Red Sea being particularly notorious.

Early Records of Guinea Worm Disease

Early references to dracunculiasis are uncertain, as people referred to the disease by different names, wrote in ancient languages and described things in various ways. The Papyrus Ebers may contain the oldest written reference to D. medinensis: the Egyptian document is dated to about 1550 BC, but it's thought to contain information copied from texts that were from earlier dates, perhaps a thousand years earlier or more.

The reference in the Papyrus Ebers that scholars think relates to Guinea worm describes “a swelling... in any limb of a man... it goes and comes, piercing through the flesh which is under it...” (translation quoted in Hoeppli).

Others describe the parasite as well, some with various remedies for dracunculiasis, though writers were unsure exactly what they were dealing with. Even as late as the 1700s, scientists disagreed as to whether D. medinensis was a worm, a vein, a nerve, an abscess, or even a piece of plant material.

Everyone agreed on one thing however: the condition caused untold misery and hardship.

The widespread misery may have been enough to give the worm a lasting place in history and Western culture. One theory suggests the Guinea worm inspired the traditional medical symbol still used today - the rod of Asclepius, which features a serpent wound around a stick.

Dracunculus medinensis may also be the “fiery serpent” that inhabited the land around the Red Sea – the serpent that bit and killed so many of the Children of Israel in the Old Testament book of Numbers.

Guinea Worm's Spread and Retreat

Step wells in South Central Asia were built to allow water
levels to change drastically. People walked right into the
water to access it. Wells like this one supplied many people
and encouraged the spread of Guinea worm.
 Image by Chetan. CC BY-SA 3.0

How this fiery serpent spread so far and wide is clear once one understands the Guinea worm's life cycle: it relies upon a dry environment where relatively few sources of water draw people together to drink, wash, and sooth their excruciating Guinea worm lesions in cool water. There also the intermediate host, a tiny crustacean, flourishes; it eats the worm's larvae and in turn is swallowed by thirsty humans, who may then move on to some other locale, some other waterhole.

How the fiery serpent has been driven back is also clear once one understands that two things will break the life cycle: people with Guinea worm lesions must not immerse their lesions in drinking water, and people who take drinking water from ponds and wells that might harbour the parasite must filter out the tiny water crustaceans before drinking.

Extinction of the Guinea Worm

Since the 1930s, cultural changes, chemical treatment of water sources, health education, and simple water filtration have had the worm in retreat from the north and east of its range. A Guinea worm eradication program, spearheaded by the Carter Center and in progress since 1984, has now pushed the parasite to near extinction. Less than 600 cases were reported in 2012, most of them in the African country of South Sudan. It's virtually certain that the story of the dreadful Guinea worm is about to end, forever.

Resources

Beaver, Paul Chester; Jung, Rodney Clifton et al. Clinical Parasitology 9th ed. (1984). Philadelphia: Lea and Febiger.

WHO Collaborating Center for Research, Training, and Eradication of Dracunculiasis, Center for Global Health, Centers for Disease Control and Prevention. "Guinea Worm Wrap-Up #216." (Jan 17, 2013). Accessed June 19, 2013.

Drisdelle, Rosemary. Parasites: Tales of Humanity's Most Unwelcome Guests. (2010). University of California Press.

Hoeppli, R. Parasites and Parasitic Infections in Early Medicine and Science. (1959). University of Malaya Press.

Premium Times. Nigeria Seeks Support on Guinea Worm Eradication. (May 17, 2013). Accessed May 21, 2013.

The Carter Center. "Guinea Worm Disease Eradication." Accessed May 22, 2013.

Symptoms of Elephantiasis (Lymphatic Filariasis)

“Elephantiasis… drew the attention of the physicians and laymen from early times on account of the often grotesque and horrible disfigurement of the patient” (Hoeppli, 33).

Lymphatic filariasis, or elephantiasis, is one of those diseases that manages to convey both its best known symptom and its special horror in a single word: its common name. Elephantiasis. Limbs as thick and gnarled as three trunks, a scrotum so enlarged that it has to be carried around in a wheelbarrow, dreadfully swollen heavy breasts.

That’s what elephantiasis is, but when it’s caused by parasites – worms living in the lymph vessels – the underlying infection is lymphatic filariasis. This is a disease of the tropics: Africa, much of Asia, Australia and islands in the Pacific, even parts of South America and the Caribbean. It is transmitted by mosquitoes.

This map shows areas of the world where lymphatic filariasis had a
severe impact in 2004. The darker the colour, the greater the impact.
Map by Lokal_Profil CC BY-SA 2.0

Asymptomatic Lymphatic Filariasis

Many people who harbour filarial worms never have any symptoms. Fetal exposure to the worm antigens in infected women appears to result in some level of tolerance in children.

It’s thought that elephantiasis only develops after many years and repeated infection; thus, though children are infected at an early age in areas where the disease is found, symptomatic lymphatic filariasis is a disease of adults.

Acute Lymphatic Filariasis

Researchers are not sure what causes an asymptomatic infection to progress to inflammation of the lymph vessels and lymph nodes, fever and chills, and swelling of tender affected limbs. It may be the death of the adult worms, which live for perhaps a decade. At this stage, bacteria are present in inflamed tissues, and these may originate from the victims skin or from the worms themselves: filarial worms are known to carry symbiotic bacteria that the human immune system reacts to.

The acute phase often also brings enlargement and inflammation of the testes, however symptoms typically subside in about a week.

Elephantiasis

The slide toward elephantiasis begins when the lymph vessels become enlarged and blocked as a result of the presence of adult worms. Lymph accumulates in the tissues instead of flowing through the vessels back to the bloodstream, and permanent swelling occurs with thickening and folding of the skin. Scar tissue forms, the urine becomes milky with lymph fluid, and bacterial infection is common.

Interestingly, when visitors to an affected region acquire the infection the immune response is different because they have not been exposed since infancy. For these people, symptoms may include inflammation of the lymphatic system that waxes and wanes over many years.

Roberts and Janovy point out that the name elephantiasis is nonsense, since it literally means “a disease caused by elephants!” I suppose, however, that if it seemed like you were turning into an elephant, the name would seem about right.

Further reading:

Hoeppli, R. Parasites and Parasitic Infections in Early Medicine and Science. University of Maylaya Press, 1959.

Hotez, Peter J. Forgotten People, Forgotten Diseases. Washington: ASM Press, 2008, 39 – 47.

Roberts, Larry S., and John Janovy Jr. Gerald D. Schmidt & Larry S. Roberts’ Foundations of Parasitology 8^th ed. Boston: McGraw Hill, 2009, 463 - 468.

Elephantiasis and Wolbachia: The Bacteria Behind the Worms

Horrific parasites sometimes turn out to be mere vessels.

Filarial worms, nematodes that are transmitted by insects and live in the tissues, cause horrible disfigurement, disability, blindness. The common names for the diseases they cause are descriptive and apt: elephantiasis, and river blindness.

Wucheria bancrofti, and Brugia malayi nematode worms live in human lymph vessels. Prolonged presence of the worms there often results in the affected part – often a limb or the scrotum - becoming grossly enlarged and deformed. Microfilaria, the worm’s young, circulate in the blood.

Elephantiasis results in almost
unbelievable disfigurement of
various parts of the body.
Imagine living with this.
Tropenmuseum of the Royal
Tropical Institute (KIT)
CC BY-SA 3.0

Onchocerca volvulus adults live together in nodules in the skin. Their young migrate through the skin and, over the long term, can cause discoloration, aging, and sagging of the skin. Worse, microfilariae in the eyes cause blindness.

For a long time, we thought that the worms themselves, and the microfilariae, caused these terrible responses to infection – that the battle between the human body and the worms caused blindness and disfigurement. But now it’s becoming clear that the real culprit is not the worms, but a type of bacteria living inside the worms. The problem is Wolbachia pipientis.

Wolbachia and Filarial Worms

Wolbachia is best known for living in insects, where it is typically parasitic and sometimes causes fatal disease. In nematodes, the relationship is different. In nematodes, Wolbachia is a symbiont: the bacterium actually provides nutrients to the parasitic worm that the worm can’t otherwise get, and without the Wolbachia, the worm can’t survive.

Researchers now have compelling evidence that what the human immune system responds to is actually the Wolbachia, not the filariae or the microfilariae. It’s the Wolbachia that causes elephantiasis and river blindness.

Wolbachia, Filarial Nematodes’ Achilles Heel

Treatment of the diseases caused by filarial nematodes has proven difficult for many reasons, not the least of which is that few drugs kill the adult worms. The discovery of their reliance on Wolbachia reveals a weakness that may be the worm’s undoing: instead of finding a drug to kill the worms, we can use a drug to kill the Wolbachia.

Ironically, if it’s the Wolbachia that’s actually the culprit, the worms end up as collateral damage.

Schistosomes: The Snail, the Prawn, and the Dam

It’s a story that has played out in Africa all too often. A river is dammed to control flooding, or for hydroelectric power, or to create a water reservoir in case of drought (or all of the above at once). The dam, of course, creates a large lake and lots of good habitat along the shore for aquatic plants, which in turn support a large snail population.

Schistosome Life Cycle

People come to live near the water’s edge, to use the water and to fish. Generally, human contact with water is high, particularly for children and fishers. If schistosomes are present, along with the right snail species, escalating levels of schistosomiasis soon follow. This is how it works:

• People infected with schistosomes pass the eggs in urine or feces, and if those eggs find their way into fresh water, they hatch.

• The emerging larva seeks out an aquatic snail – only the right snail will do – and penetrates the snail, after which it multiplies asexually in the snail’s tissues.

• Larvae leave the snail host and, if a human enters the water, penetrate human skin, maturing to adult worms that reside in the tiny blood vessels around the bladder or intestine.

• Adult worms produce eggs which are passed in the urine or feces, and so on.

It makes perfect sense that water resource projects can result in rapidly increasing incidence of schistosomiasis because they bring together the two hosts of the parasites – the human and the snail – in circumstances ideal for transmission. We hardly need a more complicated explanation. It seems, however, that there’s at least one other factor that’s been left out: the African river prawn.

River Prawns and Schistosomes

River prawns are not small!
This is Macrobrachium carcinus (molt).
Clinton & Charles Robertson. CC BY 2.0

Fascinatingly, the adult river prawn lives in fresh water, but the young require brackish water – a mixture of river water and sea water – in order to survive. When we dam an African river, we cut off access to the river’s mouth where the water is brackish. Adult prawns cannot migrate downriver; young prawns cannot migrate upriver. The prawn population upstream of the dam is doomed. And what do prawns eat? Lots of things, but one of those things is snails.

So just as the dam provides beautiful habitat for the proliferation of snails, it also wipes out a key predator of those snails. Instead of tasty prawns, people living on the shores of the reservoir get schistosomiasis. That’s a bad deal.

At least one project – Project Crevette - is now rearing the prawns and releasing them into an affected river, effectively reducing the level of schistosomiasis and providing food and marketable prawns for the people in the area. That’s a good deal.

Michael B. New writes that postlarvae (the stage of prawn young that migrate upstream) of at least one species “can climb vertical surfaces and cross land, provided there is abundant moisture available” (Farming Freshwater Prawns: A Manual for the Culture of the Giant River Prawn Macrobrachium rosenbergeii. Food and Agriculture Organization of the United Nations, 2003, pg 10). One wonders how difficult it would be to re-establish the natural life cycle of the river prawn.

Manure and Latrines = Farming and Parasites

Pig sties are notoriously smelly places, but aged
pig manure makes excellent fertilizer.
 Image by MontagZen; CC BY-SA 3.0.

Almost twenty years ago, Jared Diamond wrote about the domestication of plants in Discover  ("How to Tame a Wild Plant," Sept 1994). "Human latrines," he wrote, "may have been a testing ground for the first crop breeders."

How so? Many plants get spread around when their seeds are eaten, passed through the digestive tract of the forager intact, and deposited in feces. Because humans tend to use latrines - designated outdoor toilets that they return to again and again - the seeds of the plants that early humans liked to eat got deposited in a concentrated area, and the wastes deposited with them provided fertilizer. Voila! Latrines would have effectively selected the choicest food items of early humans and aided their reproduction.

Because I'm interested in parasites, I couldn't help thinking that this very process also aided the transmission of intestinal parasites: choice food plants growing in areas used as latrines means people gathering food there, with resulting exposure to the eggs and larvae of intestinal worms (and probably protozoa as well).

"Our ancestors' garbage dumps," Diamond pointed out, "undoubtedly joined their latrines to form the first agricultural research laboratories." This, because larger seeds, roots and other plant parts that might reproduce would end up in the midden, or garbage dump, along with all the other food waste (think compost) and animal manure (if they had livestock), gaining a survival advantage in virtually the same way.

And now, in his article "Early Farmers and Manure: Stone Age Europeans Were More Advanced Than We Thought," (Decoded Past, July 3013) Frank Beswick reports on evidence that stone age people used animal manure as fertilizer as long ago as 6000BC. Beswick wonders "is it possible that the use of manure was a precondition of the development of agriculture?"

And I wonder how much it contributed to the parasites we share with domestic animals, particularly cattle and pigs.

Pinworms and Human Immunity

Thoughts on pinworm infections...

I had a strongly worded email from someone who had apparently read, and taken exception to, one of my articles about pinworm (Enterobius vermicularis). I was a little surprised by the tone of the email - who knows why someone would become attached to this particular soapbox - but the vehement claim that the human immune system will eradicate a case of pinworm (enterobiasis) got me thinking.

One female pinworm can produce 10,000 sticky eggs.

Mentnafunangann; CC BY-SA 3.0

Will Pinworm Infection Resolve Without Treatment?

I’m of the understanding that a pinworm infection will resolve on its own eventually if left untreated – and I never said otherwise – but what role does the immune system play? Can the immune system kill the adult worms? We know that the immune system responds to parasites, but many parasites are good at evading immune attacks, and prompting moderation of the immune response. Enterobius vermicularis should be particularly good at this because it is one of our heirloom parasites: it’s been with us hundreds of thousands of years.

Add to this the frequently reported problem of reinfestation through swallowing eggs in the home/school environment and one begins to suspect that waiting for the immune system to do the job could be a long process. It’s clear that, for many people, the immune system is ineffective at eliminating the adults (they likely die of old age after a month or so), and unable to effectively kill larvae over the long term after initial exposure.

Having said all that, it probably doesn’t matter all that much, except for those unfortunate individuals that experience bad symptoms.

A Realistic Approach For Pinworm Infection

Further thoughts:

• Texts tell us that the majority of pinworm infections are asymptomatic, so lots of people have pinworms, don’t suffer any unpleasant symptoms, and eventually eliminate the worms on their own. (And if they have no symptoms, they’re less likely to spread it around.)


• The ability to fight off enterobiasis likely varies from one person to the next, as it appears to with other parasitic worm infestations.


• An overzealous approach to eradicating pinworms is probably unrealistic.  They’re so good at spreading themselves around, and we’re so poor at fighting them off, that actually getting rid of them is next to impossible.


• When symptoms are severe and persistent, however, only the most stoic of patients would refuse treatment. I’ve never had the pleasure myself, but I’ve heard first hand accounts that were not pretty.

I suspect most people would choose to treat a pinworm infection but it's up to the individual.