Leeches are still used in modern hospitals and clinics around the world. This practice, known as hirudotherapy, has experienced a significant revival, particularly in reconstructive surgery since the 1980s. The medicinal leech is a tool used by medical professionals for specific, scientifically validated purposes. Today, leeches are specially bred under controlled, sterile conditions for patient use.
The Modern Medical Leech
The primary species utilized is the European medicinal leech, Hirudo medicinalis, although species like Hirudo verbana are also used. These organisms are strictly managed and raised in sterile bio-farms to prevent pathogen transmission, addressing a major historical concern. Every leech used is a single-use biological device and is never reused between patients. In the United States, the Food and Drug Administration (FDA) cleared the medicinal leech for commercial marketing in June 2004. The FDA classified the leech as a medical device, recognizing both the mechanical function of its feeding and the biological effects of its saliva.
Pharmacological Components of Leech Saliva
The leech’s therapeutic effectiveness is attributed to the complex cocktail of bioactive compounds found in its saliva, which is injected during feeding. The saliva contains over one hundred biologically active substances, including anticoagulants, vasodilators, and anti-inflammatory agents. These compounds work synergistically to maintain blood flow and prevent clotting at the bite site.
Hirudin is the most famous component, acting as a potent anticoagulant. It directly binds to thrombin, a protein central to the blood clotting cascade, effectively inhibiting clot formation. Another enzyme is Hyaluronidase, which functions as a “spreading factor.” It temporarily breaks down hyaluronic acid, increasing tissue permeability and allowing other therapeutic substances to spread more effectively. The saliva also contains Calin, a platelet aggregation inhibitor that helps maintain blood fluidity by disrupting the initial phase of clot formation.
Specific Clinical Applications
The main indication for modern hirudotherapy is to relieve venous congestion, a common and serious complication in microsurgery. Venous congestion occurs when arteries successfully pump blood into reattached or transferred tissue, but the veins cannot drain it adequately, causing pooling. If unresolved, the tissue becomes deprived of oxygen and nutrients, leading to tissue death.
Leeches are frequently used in reconstructive plastic surgery, especially following the reattachment of severed body parts like fingers, ears, noses, and lips. They are also used to save compromised skin grafts and flaps. In these procedures, delicate veins are often difficult to repair, and leeches provide a temporary solution. By attaching to the congested site, the leech mechanically removes pooled venous blood. Simultaneously, the salivary components prevent new clots and promote continued, gentle bleeding for up to 48 hours after removal. This sustained drainage reduces capillary pressure, creating a bridge until the body establishes new venous pathways to drain the tissue. The therapy is often used as a last resort to salvage tissue, with high reported success rates.