Scientific Success Story – Dracunculus medinensis

Dracunculus medinensis, also known as the Guinea Worm, has been the cause of parasitic infection in humans for hundreds of thousands of years.

This worm is the largest of the tissue parasite affecting humans. The adult female, which carries about 3 million embryos, can measure 600 to 800 mm in length and 2 mm in diameter. The parasite migrates through the victim’s subcutaneous tissues causing severe pain especially when it occurs in the joints. The worm eventually emerges (from the feet in most of the cases), causing an intensely painful oedema, a blister and an ulcer accompanied by fever, nausea and vomiting.

It is also unique in that it requires a human host for a part of its life-cycle.

The larval stages are hosted by water borne copepods that are ingested by humans via infested water. The mature worm can reach 3 feet in length, and cause an itching/burning sensation that leads to the use of water to cool the affected limb. The next generation of larvae is then released into the water to continue the cycle.

In 1986, there were an estimated 3.5 million people infected with guinea worm. This inspired ex US President to begin an eradication process.

That community-driven process, coördinated by the Carter Center and executed by the South Sudan Ministry of Health, village volunteers, and trained technical advisors, is driving the parasite out of its last remaining human hosts. Each person known to be infected with the worm, along with every village in which outbreaks have occurred or are occurring, is tracked. Intervention is multi-pronged: the infected are quarantined, since patients with emergent worms must be kept away from water sources; containment-care facilities welcome not just the victims but their dependents, too; local education programs focus on water filtration.

These efforts have resulted in only 542 reported cases in 2012 and only 35 in the first 4 months of 2013. Mark Sidell, the author of the New Yorker article describes some additional and unforeseen benefits of these programs.

Many years ago, when I was beginning a career in parasitology, I was told about the “parasitologists dilemma,” a spin on the Malthusian catastrophe. The premise was that, should parasitologists actually manage to eradicate infectious diseases caused by parasites, we’d be morally responsible for thrusting millions of people into the inevitable conflict and poverty that would result from population growth and increased pressures on a limited food supply. But in every place where the guinea worm has been eliminated, the very opposite is true. Just a couple of decades ago, Ghana and Mauritania had thousands upon thousands of cases. Now, both countries are free not only of guinea worm but, increasingly, of the shackles of poverty: per capita G.D.P. has tripled, the number of people living on less than a dollar a day has been halved, and the birth rate has plummeted. This, obviously, is the result of many factors besides guinea worms. But I can say this: so much for Malthus.

The modern era has sometimes been referred to as another great extinction event (holocene extinction) to rival those of the past. Although this comparison is debatable, some extinctions, such as Dracunculus medinensi, are not in the least regrettable.

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