Mechanisms of Leech Therapy

The leech's ability to sustain venous blood flow, in compromised skin flaps, is currently unmatched by any other means. The leech performs its service by physically evacuating blood and ensuring continued blood flow long after the leech detaches. The shape of the leech incision and substances in its saliva keep the blood flowing.

• Anticoagulants: Hirudin is one of many anti-clotting agents contained in the leech's saliva. Its purpose is to inhibit coagulation while the leech feeds. Hirudin has a high affinity for thrombin, binding and blocking its activity at very very low concentrations. Thrombin converts circulating fibrinogen into fibrin, creating an insoluble clot.
  • Other salivary components inhibit substances involved in platelet aggregation, including: adenosine diphosphate, epinephrine, platelet-activating factor and arachidonic acid.
• Anesthetic: In the wild, leeches are usually not noticed by prey until they have been feeding for sometime. A natural anesthetic that minimizes host discomfort is presumed but as yet unidentified.
• Anti-inflammatory: Leech saliva contains substances which inhibit the metabolism of arachidonic acid to prostaglandin. Prostaglandins are known to contribute to the pain, heat and swelling associated with the inflammatory process.
  • A number of small studies indicate that leech therapy may relieve the pain associated with osteoarthritis.
    

A leech can usually suck an average of 5 milliliters (ml) of blood within 15 to 60 minutes, but the real effect comes after the leech detaches. The bite can continue to bleed for up to 48 hours, releasing as much as 50 ml of blood. Usually treatments are carried out for 3 to 7 days, occasionally as long as 10 days. When the skin stays pink after leech therapy and venous oozing stops, the leech therapy can usually be discontinued.