Thursday, April 19th, 2007--

Leeches are experiencing a medical renaissance: the Food and Drug Administration recently approved the use of Hirudo medicinalis, known as the European medicinal leech, as a medical device. Prized for their anti-coagulants, leeches are used after surgery to improve blood flow in places where skin was reattached. Increased blood flow helps tissue survive.

“Leeches really hit their heyday in the mid-1800s, going into the early 1900s,” says Mark Siddall, a leechologist and associate curator at the American Museum of Natural History in New York City.  One of Napoleon’s surgeons popularized leech-use when he realized that “instead of just slicing peoples' veins open for the purposes of blood-letting and balancing humors, you could use leeches and control the amount of blood being removed,” Siddall says. Because it has been used for so many years, H. medicinalis has a rich history in the medical literature, Siddall says, and has been pegged as the sole European medicinal leech.

Research by Siddall and his colleagues, however, published in Proceedings of the Royal Society B: Biological Sciences, shows that the European medicinal leech is not one species, but at least three. Joining the ranks of medicinal bloodsuckers are Hirudo verbana and Hirudo orientalis.

In fact, Siddall and his co-authors Peter Trontelj from the University of Ljubljana in Slovenia, Serge Utevsky from the V. N. Karazin Kharkiv National University in Ukraine, Tripp Macdonald of Rutgers University, and Mary Nkamany, an undergraduate from the City University of New York, discovered that commercial leeches (there is a leech farm in New York called Leeches USA) are largely mislabeled. These commercial leeches, which end up in scientists' labs and even on hospital gurneys, are almost exclusively H. verbana. “What was particularly unnerving is that what is being distributed by commercial outfits—the leech farms—all prove to be Hirudo verbana, not Hirudo medicinalis.”

This controversy isn’t new however. In the 1800s, a French scientist claimed multiple species existed, but then repudiated his own findings twenty years later. The debate was reignited in 1999, when two European researchers, “in a somewhat obscure chapter of a book,” claimed there were two species of medicinal leech, Siddall says. Evidence has been mounting since, and thanks to DNA barcoding and other cutting-edge genetic testing techniques, Siddall was able to corroborate the claim that the European medicinal leech is not only H. medicinalis.

The three leech species aren’t so different from one another. But that’s not really the point, Siddall says: “The underlying problem is that we now have 20 to 25 years of scientific literature where everything is potentially mislabeled.” Neurobiologists study leeches because the creatures have large neurons and relatively complicated behavior.

Siddall adds, “It’s not that there has been any malfeasance on anyone’s part—we all thought there was really only one species. At the same time, there is a bit of sociology going on because there is not a lot of cache in working on Hirudo verbana, when Hirudo medicinalis is the European medicinal leech.” On the up side, this finding raises the possibility that three times as many anti-coagulants or potential cancer medicines exist, Siddall says.

But we are losing our leeches. A century of unchecked leech-gathering (Siddall says tens of millions were harvested annually in the 1800s) and wetland destruction decimated the European medical leech population. Today, H. medicinalis, but not H. verbana and H. orientalis, is considered a “threatened species” and afforded protection under several international treaties. Siddall's study may mean that European medicinal leeches are in worse shape than previously thought. Siddall says: “We already know that medicinal leeches are threatened in Europe and that was when we thought there was only one species, now that we see it is multiple species, the situation could be much more dire.”

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--Flora Lichtman

Sources

Mark Siddall
Associate Curator Division Of Invertebrate Zoology American Museum Of Natural History New York, New York

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