Scientific Name(s): Hirudo medicinalis L. Phylum: Annelida.
Common Name(s): Fresh water leech, Medicinal leech
Medically reviewed by Drugs.com. Last updated on Apr 26, 2021.
Leeches have been used for bloodletting, wound healing, and stimulating blood flow at postsurgical sites. Use in osteoarthritis is being investigated, but there is a lack of clinical information to make recommendations.
Consult existing guidelines for the use of leeches.
Arterial insufficiency, previous exposure to leeches (risk of allergic reaction), immunosuppression (risk of infection), patient refusal to accept possible subsequent blood transfusions, and unstable medical conditions have been described as contraindications for extensive leech therapy.
Information regarding safety in pregnancy and lactation is lacking. Avoid use because of risk of infection and anemia.
None well documented.
Extensive blood loss. Allergic reactions and infections may develop.
There are more than 700 species of leeches, all of which are carnivorous.1 The leech is an hermaphrodite, containing both male and female sexual organs, but is not self-fertile.
The use of medicinal leeches (H. medicinalis) is preferred because of their ability to bite deeply and cause prolonged bleeding even after they are detached. H. medicinalis can reach up to 12 cm long, but is generally smaller, weighing 1 to 1.5 g before feeding. H. medicinalis has both anterior and posterior suckers, with the head located at the narrow tapered end. The anterior sucker has 3 jaws, each with 60 to 100 teeth for biting. The posterior sucker is used for attachment and crawling.1
Leeches obtained from commercial breeders are easily maintained in a chlorine-free salt solution at 10° to 20°C. Under such conditions, leeches can survive for up to 18 months.
The medicinal use of leeches dates back to ancient Egyptians around 1300 BC; the Greek physician Galen (130 to 201 AD) commonly used leeches for bloodletting. The 19th century heralded the widespread use of leeches for bloodletting—leading to a leech shortage from 1825 to 1850 in France requiring the importation of leeches from America.1, 2, 3, 4, 5, 6 By the end of the 19th century, the medicinal use of leeches had lost popularity due to adoption of the modern concepts of pathology and microbiology.1
Following attachment, H. medicinalis secretes hirudin, a selective thrombin inhibitor, which enhances bleeding and prevents coagulation.1, 9, 10 Hirudin was first described more than a century ago and characterized as a 65-amino acid peptide with antithrombokinase activity.1 Early therapeutic studies of hirudin were limited by low natural yield, but the compound has recently been produced in larger quantities by recombinant gene techniques.11, 12 Recombinant hirudin binds avidly to thrombin, thus low doses inhibit venous thrombosis in animals. Extracts from leeches have been marketed in creams for topical application. In addition to hirudin, leeches secrete hirustasin, which selectively inhibits tissue kallikreins; antistasin and ghilanten, which inhibit Factor Xa; calin, apyrase, and saratin, which inhibit platelet aggregation; a histamine-like compound, which causes vasodilation; hyaluronidase and collagenase, which increase permeability; and bdellin and eglin, which are proteinase inhibitors.1, 10, 13, 14
There is conflicting evidence as to whether an anesthetic is secreted in H. medicinalis.4, 15, 16 Theromyzon is widely distributed in the tissue of the leech Theromyzon tessulatum and has angiotensin-converting, enzyme-like properties8 and peptides with antimicrobial properties have been identified.17
Uses and Pharmacology
After attaching to the site, leeches secrete compounds, especially hirudin, that reduce blood viscosity. They provide the drainage needed to permit decongestion and to preserve tissue viability until normal venous flow is established.16, 20
Based on reported anti-inflammatory substances in the saliva of medicinal leeches, a number of clinical studies have evaluated the role of leeches in osteoarthritis.18, 19 Blinding of participants is problematic in such studies and comparators have used transcutaneous electrical nerve stimulation (TENS)23 and topical diclofenac.24 A meta-analysis of clinical studies (n=4) reported moderate to strong evidence for pain reduction, functional impairment, and joint stiffness following leech therapy.19
Institutional guidelines may exist for the use of leeches. Leeches are applied from 2 to 4 times a day for up to a week. Feeding is complete in about 20 minutes, at which time the leech drops off. Removal of the leech may be hastened by applying solutions of salt, vinegar, a flame, or a local anesthetic. Leeches should not be forcibly removed. Bleeding from the attachment site usually continues for several hours. Reuse of leeches is discouraged to minimize the development of cross-infection.1, 20, 25, 26
Pregnancy / Lactation
Information regarding safety in pregnancy and lactation is lacking. Avoid use due to risk of infection and anemia.
None well documented. Closely monitor conditions requiring concomitant anticoagulant therapy.
One study found no changes in ipsilateral activated partial thromboplastin or prothrombin times when leeches were applied to an intact hand. This suggests that systemic or local anticoagulation is not likely to occur and that the risk of interference with other therapies may be small.27
Arterial insufficiency, previous exposure to leeches (risk of allergic reaction), immunosuppression (risk of infection), patient refusal to accept possible subsequent blood transfusions, and unstable medical conditions have been described as contraindications for extensive leech therapy.9
Leeches may consume up to 50 mL blood per application, and their secretions during a single feed can prevent coagulation (in vitro) of up to 100 mL human blood. Passive bleeding after detachment can continue up to 72 hours but most commonly continues for about 5 hours. Blood loss may occur, sometimes requiring transfusions.18, 28
The gram-negative Aeromonas hydrophilia is the predominant microbial species found in leeches.1, 9, 29, 30 Serratia, Klebsiella, and Pseudomonas have also been isolated10, 31, 32, 33, 34 and patients should receive appropriate prophylactic antibiotic therapy. Older studies suggested possible transmission of HIV and hepatitis, but this is less likely with the use of farmed leeches.22, 35 Reuse of leeches is not recommended due to concerns of disease transmission.4
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