Genetic research 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.
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 treatments – some legitimate, many not. Demand for leeches in 19th-century Europe grew so intense that efforts to protect them led to 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 US Food and Drug Administration (FDA) for use as a prescription medical device that helps restore blood flow following cosmetic and reconstructive surgery – provided that accurate labelling 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: the FDA has not approved Hirudo verbana and it has no special conservation status.
“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 American Museum of Natural History.
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 labelled, 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 tantalising 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.”
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