Medicinal leeches aren't one species, but three, a finding that may affect hundreds of scientific papers
By Kirsten Weir | May 2, 2007
A recent genetic analysis of the medicinal leech has revealed that one species should be classified as three, and suggests that many leeches sold commercially have been misidentified -- oversights that may have a significant impact on years of research involving leeches.
Biochemists have isolated dozens of pharmaceutical compounds from leeches, including anticoagulants, analgesics, and protease inhibitors. Leeches are also used as model organisms in neurobiology, developmental genetics, and enteric symbiosis. Now, scientists can't be entirely sure which species they may have studied. "This raises issues about hundreds of articles," Mark Siddall of the American Museum of Natural History told The Scientist.
In the study, released in April on the Web site of the Proceedings of the Royal Society B, Siddall and his colleagues found that the species known as Hirudo medicinalis should, in fact, be classified as three distinct species. What's more, all of the leeches sold commercially under the name Hirudo medicinalis that the scientists tested were actually a different species, H. verbena.
According to Siddall, current leech taxonomy dates to 1827, when French zoologist Alfred Moquin-Tandon published a description of several Hirudo species. "In 1846, he changed his mind," Siddall said, and determined that the species he'd described were actually just different color variations of H. medicinalis, which became the species name for all medicinal leeches. In the past decade, however, scientists began suggesting that perhaps Moquin-Tandon's first instinct was correct.
Analyzing nuclear microsatellites and mitochondrial sequences from wild European medicinal leeches, Siddall's team concluded that three distinct species exist: H. medicinalis, H. verbena, and H. orientalis. "It is absolutely impossible that H. verbena and H. medicinalis are sharing any DNA...even though they can co-occur in the wild," Siddall said. "This demonstrated beyond a shadow of a doubt that they are distinct species."
Siddall and his team also analyzed ten leeches from the four principal commercial suppliers, as well as from two research laboratories. Although these were labeled H. medicinalis, they found all were actually H. verbena. "Not a single H. medicinalis in the bunch," he said.
Although the finding has an implication for biologists working with leeches, W. Otto Friesen, who studies leech neurobiology at the University of Virginia, doesn't anticipate a major fallout, simply because the differences between leech species may have no influence on any data. "Until I do [experiments to compare the species], I'm pretty comfortable that there aren't any big differences [between them]." For Friesen, the biggest question is a technical one. "At what point do I start reporting that I'm using H. verbena?" he wondered.
Rethinking leech taxonomy could prove a trickier issue for the increasing number of physicians who use leeches to promote blood flow following reconstructive surgery. In 2004, the FDA cleared H. medicinalis for use as a medical device.
Rudy Rosenberg, owner and vice president of commercial supplier Leeches USA Ltd in Westbury, NY, one of the suppliers Siddall and his colleagues tested, told The Scientist that H. medicinalis and H. verbena are medically "interchangeable." His company receives leeches from Ricarimpex, a French leech farm that first petitioned the FDA to approve H. medicinalis. If Siddall's results are corroborated and the scientific community accepts the new classification, Rosenberg said, his company or Ricarimpex would likely ask the FDA to extend approval to H. verbena.
According to FDA spokesperson Karen Riley, "other species of medicinal leeches may be cleared for commercial distribution in the US, if they are found to be 'substantially equivalent' to a legally marketed medicinal leech."
Meanwhile, Siddall said he is concerned about the conservation implications of his study. H. medicinalis is listed as an endangered species, but H. verbana and H. orientalis are not. If wild leeches comprise three distinct species rather than one, Siddall noted, each one's status is even bleaker than realized. "Now, whatever the numbers and health of those populations were," he said, "it must be worse than we thought."
Image: H. medicinalis (A), and H. verbena (B). From the Royal Society.
Links within this article:
Baskova et al, "Protein profiling of the medicinal leech salivary glad secretion by proteomic analytical methods," Biochemistry (Mosc). 2004
SPIS MedWire: "Leeches give bite to arthritis care," The Scientist, September 18, 2001.
Sollner et al, "Isolation and characterization of hirustasin, an antistasin-type serine-proteinase inhibitor from the medicinal leech," Eur. J. Biochem 1994.
Siddall ME, Trontelj P, Utevsky SY, Nkamany M, and Macdonald KS, "Diverse molecular data demonstrate that commercially available medicinal leeches are not Hirudo medicinalis." Proceedings of the Royal Society B: 2007, Vol. 274: 1481-1487.
N. Atkinson: "Taxonomy isn't black and white," The Scientist, September 28, 2004.
W. Otto Friesen
WB Kristan Jr et al, "Neuronal control of leech behavior," Prog. Neurobiol. 2005.
Leeches USA Ltd