Thursday, 20 February 2014

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.

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