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Suckers for success

The use of leeches is making a comeback, and not just in medicine.

In the 1807 poem Resolution and Independence, William Wordsworth recalls a dawn encounter with a withered old man on a moor: “He told, that to these waters he had come | To gather leeches, being old and poor: | Employment hazardous and wearisome!”

Nineteenth-century gatherers often dunked their legs into leech-filled bogs and ponds until the bloodsuckers began to feast. The motivation was money: medical use of leeches, or hirudotherapy, was at its height in Europe, and surgeons needed every leech they could get. France reportedly imported 42 million medicinal leeches in 1833 alone.

Leech therapy dates to ancient Greece, and perhaps earlier. Hippocrates preached the importance of balancing the four humours (blood, phlegm and black and yellow bile) through bloodletting. Because they secrete a host of enzymes to anaesthetize their victims at the spot of a bite and to keep the blood flowing, leeches were useful when drawing blood from sensitive parts of the body such as the mouth, larynx and anus.

Nicander of Colophon, who lived in the second century BC, described the medical use of leeches, which belong to the same phylum (Annelida) as earthworms, in his poem Alexipharmaca. Greek, Roman and Arabic doctors embraced their use, and English doctors in the Middle Ages were often called leeches; the Anglo–Saxon word læce means healer.

The leech bubble burst in the second half of the nineteenth century, when people realized that the animals made most patients worse, not better. By 1879, London's leading leech importer was distributing just a tenth of the 30,000 or so it once had, and they “principally go to Scotland”, the British Medical Journal noted that year.

Still, the leech has never really left the medical mind, and it is starting to be used again. Reconstructive surgery, always a hotbed of innovation, was the first field to re-embrace the medicinal leech (Hirudo spp.). A survey of the 62 plastic-surgery units in the United Kingdom and Republic of Ireland in 2002 found that 80% had used leeches in the past five years, with just four centres reporting that a patient had turned down hirudotherapy (I. S. Whitakera et al. Br. J. Plast. Surg. 57, 348–353; 2004). No wonder. Leeches are thought to improve the outcomes of reattached digits, ears and other body parts by preventing veins from becoming clogged.

Leeches also ease the pain caused by osteoarthritis. Among the 30 or so biologically active substances in their saliva are molecules that stop inflammation and blood clotting, both of which are involved in arthritis.

Medical-grade-leech sales haven't returned to their early-nineteenth-century heights, but the animals are once again selling briskly. Britain's largest supplier, Biopharm Leeches in Hendy, Wales (which has the tag line “The biting edge of science”), ships around 50,000 per year, and in 2004, a French firm, Ricarimpex in Eysines, won clearance from the US Food and Drug Administration to market its leeches as medical devices in the United States.

Leech use is not restricted to medicine. As we report on page 424, tropical leeches are being recruited in the search for endangered species. These leeches preserve DNA from the last mammal they fed on, so can offer clues to the mammal's range and location. Conservationists in Vietnam and Laos plan to scour the bellies of leeches in their search for the saola antelope (Pseudoryx nghetinhensis), one of the world's rarest animals.

It is a fitting twist for the medical leech, which itself is listed as a 'near threatened' species in the wild and may have been in decline even in Wordsworth's time. “Once I could meet with them on every side,” the old leech gatherer tells the young poet. “But they have dwindled long by slow decay; | Yet still I persevere, and find them where I may.”

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Suckers for success. Nature 484, 416 (2012). https://doi.org/10.1038/484416a

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