New Research By Scientists At The American Museum Of Natural History Shows Medicinal Leeches Misclassified For Centuries, Are Likely Three Species Instead Of One
Hirudo medicinalis (top) and Hirudo verbana (bottom).
© Andrei Utevsky
Genetic research led by Mark Siddall at the American Museum of Natural History has revealed that commercially available medicinal leeches, until now assumed to be the species Hirudo medicinalis, used around the world in biomedical research and postoperative care, are actually a closely related but genetically distinct species, Hirudo verbana. Moreover, the study has shown that wild European medicinal leeches comprise at least three distinct species, not one.
The research team led by Dr. Siddall included 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 an undergraduate student from the City University of New York, Mary Nkamany. Their work will appear April 10 in the online version of the biological research journal Proceedings of the Royal Society B.
"This is the kind of impact that basic science can have on more applied disciplines like medicine and neurobiology, even if its initial implications call into question 25 years of prior work," said Dr. Siddall, Associate Curator of Invertebrate Zoology at the Museum.
Since the time of Hippocrates and long before Carolus Linnaeus first described Hirudo medicinalis in 1758, medicinal leeches have been used in a variety of medical treatmentssome legitimate, many not. Demand for leeches in 19th-century Europe grew so intense that efforts to protect them led to the some of the earliest legislative efforts at biological conservation. Leeches are still afforded protection by the World Conservation Union (IUCN) and are regulated by the Convention on International Trade in Endangered Species (CITES), the Berne Convention, and the European Union Habitat Directive.
In 2004, commercially marketed Hirudo medicinalis was approved by the U.S. Food and Drug Administration (FDA) for use as a prescription medical device that helps restore blood flow following cosmetic and reconstructive surgeryprovided that accurate labeling and branding regulations are followed. The main finding from Dr. Siddall's research, that widely used leeches are Hirudo verbana not Hirudo medicinalis, carries significant implications: Hirudo verbana has not been approved by the FDA and it has no special conservation status.
Commercially available European medicinal leeches also are used extensively by biomedical researchers studying biological processes such as blood coagulation, developmental genetics, and neurobiology. Studies of commercial specimens have figured prominently in the discovery and production of anticoagulants and protease inhibitors, some of which may have cancer-fighting properties.
"Interpretations of developmental and neurophysiological characteristics . . . presuppose uniformity within a model species used in laboratory settings," the authors write in their paper. That researchers have been mistakenly using Hirudo verbana in their work for decades may call much of this research, including hundreds of scientific publications, into question and force a reconsideration of what scientists think they know about this widely studied species.
Dr. Siddall and his colleagues examined mitochondrial and nuclear DNA of wild leeches from across their range in Europe, as well as from samples supplied by commercial providers and university laboratories that use leeches as model organisms. Their analysis clearly showed that the commercial and laboratory specimens were not Hirudo medicinalis, as they were labeled, but rather Hirudo verbana. In addition, the work showed that the specimens of wild European medicinal leeches clearly comprised three genetically distinct species.
"This raises the tantalizing prospect of three times the number of anticoagulants and three times as many biomedically important protease inhibitors as previously thought," said Dr. Siddall. "However, it will also require a more nuanced effort aimed at conserving these much-maligned animals and in a manner that takes into account their impressive diversity."
The research was supported by grants from the U.S. National Science Foundation, the Richard Lounsbery Foundation, the Slovenian Research Agency, and INTAS.
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