Mark E. Siddall

Importance to Hirudotherapy

Mark Siddall's 2007 species-correction paper in Proceedings of the Royal Society B is one of the most consequential single publications in modern hirudotherapy. Using mitochondrial and nuclear molecular markers across a broad sample of commercially supplied medicinal leeches — including specimens obtained from Ricarimpex SAS, the supplier whose product had received FDA clearance in June 2004 as Hirudo medicinalis (510(k) K040187) — Siddall and colleagues demonstrated that the leech in clinical circulation was actually Hirudo verbana, a morphologically very similar but genetically distinct species. The implication was that the FDA-cleared device on the United States market had been incorrectly identified at the species level on its regulatory submission. The practical regulatory and supply-chain implications were immediate. Ricarimpex updated its product labeling and regulatory documentation, and the FDA-cleared species identity on the United States market was corrected to Hirudo verbana. The taxonomic correction also clarified the conservation status of the leech in clinical use: Hirudo medicinalis itself is listed under CITES Appendix II and EU Habitats Directive Annex V as a protected species facing extinction in much of its native range, whereas Hirudo verbana, while also CITES-listed, has somewhat different distributional and population biology. The correction therefore had implications for both regulatory compliance and conservation policy that are still being worked through in the international leech-supply community. Siddall's broader work on leech molecular phylogeny has established the evolutionary framework within which modern compound discovery operates. The recognition that different leech species (Hirudo verbana versus Hirudo medicinalis, the various Haementeria species in the Americas, the predatory Macrobdella decora in North America) produce distinct repertoires of anticoagulant and antithrombotic compounds, and that these repertoires reflect deep phylogenetic divergence, has guided modern drug-discovery searches for novel leech-derived therapeutics. The American Society of Hirudotherapy considers him the patron of evidence-based species identity in clinical leech use — the figure who ensured that hirudotherapy is now practiced on a sound taxonomic foundation.