Diverse molecular data demonstrate that commercially available medicinal leeches are not Hirudo medicinalis

Abstract

The European medicinal leech is one of vanishingly few animal species with direct application in modern medicine. In addition to the therapeutic potential held by many protease inhibitors purified from leech saliva, and notwithstanding the historical association with quackery, Hirudo medicinalis has been approved by the United States Food and Drug Administration as a prescription medical device. Accurate annotation of bioactive compounds relies on precise species determination. Interpretations of developmental and neurophysiological characteristics also presuppose uniformity within a model species used in laboratory settings. Here, we show, with mitochondrial sequences and nuclear microsatellites, that there are at least three species of European medicinal leech, and that leeches marketed as H. medicinalis are actually Hirudo verbana. Beyond the obvious need for reconsideration of decades of biomedical research on this widely used model organism, these findings impact regulatory statutes and raise concerns for the conservation status of European medicinal leeches.

Figure 1

Distinctive colour patterns for two species of European medicinal leech. (a) Hirudo medicinalis Linnaeus 1758. (b) Hirudo verbana Carena 1820.

Figure 2

DNA barcoding distinguishes European medicinal leech species. Multiple equally parsimonious trees varied on resolution within each of the wild or commercial medicinal leech clades, and on whether Hirudo orientalis is sister to H. medicinalis or to the other European medicinal leeches. Clade support values are non-parametric bootstrap proportions. Mean genetic distances: 8.55% between wild H. medicinalis and H. verbana; 1.81% between leeches commercially marketed Hirudo medicinalis and wild H. verbana; 9.03% between leeches commercially marketed Hirudo medicinalis and wild H. medicinalis; 8.60% between H. orientalis and the other wild Hirudo species. Branch lengths are based on a GTR +G model of nucleotide substitution. A commercially obtained Hirudo medicinalis (i.e. H. verbana) is shown feeding (inset).