Monday, January 21, 2013
A Farewell to Worms
by Kevin S. Baldwin
Amidst all the bad news about climate change and emerging diseases it is easy to overlook one of the most successful public health initiatives in recent memory. We are on the verge of exterminating an ancient scourge, the Guinea worm.
Dracunculus medinensis, (literally the little dragon from Medina), is a large nematode, which can reach up to 80cm in length. Humans acquire it by drinking unfiltered water that contains water fleas (copepods of the genus Cyclops) infected with larval nematodes. As the copepods are digested, the worm larvae burrow through the human gut and mature in the body cavity. Male worms die after fertilizing females and gravid females move to subcutaneous areas typically on the lower limb. After about a year of maturation, the female releases compounds that cause the skin to blister and the host goes to water to seek relief from the painful lesion, which then ruptures, releasin g the nematode larvae into the water where they are ingested by copepods to complete the life cycle.
This worm is the fiery serpent of the Old Testament. Its treatment in ancient times (and even today), slowly winding the worm around a stick to extract it from the skin lesion, gave rise to symbols for medicine we use today: The single snake on a club (the Asklepian) and the two snakes on a winged staff (the caduceus).
As recently as 1986, 3.5 million annual cases were recorded in 20 countries stretching from West Africa to South Asia. Last year, new cases fell to just 542 in four African countries, with the vast majority (521) in South Sudan. Based on data from the Carter Center (http://www.cartercenter.org), I plotted the number of cases from 1999 (86,910) through 2012. The dramatic exponential decrease was briefly interrupted by the discovery of more worm populations that accompanied greater access to parts of Sudan in 2006. More recently, fighting in Mali may have forced infected refugees into Niger. The Four Horsemen are still with us and they still tend to amplify each other's effects.
Despite these setbacks, eradication of the Guinea worm is within our grasp and hopefully it will soon be only the second disease after smallpox to have been vanquished. Educating local people about the disease has been key. Other measures, like keeping infected individuals from entering drinking water sources, filtering water through a fine cloth or mesh (to prevent copepod ingestion), and use of a larvicide to kill worm larvae and copepods have all contributed to better control.
The cooperation of NGO's, various foundations, individuals, and governments that has gotten us to this point is to be commended. Hopefully, this kind of cooperative enterprise can be used to successfully address other complex international issues in the future.
The Carter Center (http://www.cartercenter.org).
Donald G. McNeil Jr. 2005. Slithery Medical Symbolism: Worm or Snake? One or Two?.
New York Times. March 8.Philip Palmer, MD and Maurice Reeder, MD 2005. The Imaging of Tropical Diseases. (http://www.isradiology.org/tropical_deseases/tmcr/main.htm).
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