Facts about leeches:

Leeches
Scientific Name(s): Hirudo medicinalis L. Phylum: Annelida

Common Name(s): Fresh water leech , medicinal leech

Clinical Overview
Uses of Leeches
Leeches have been used for bloodletting, would healing, and stimulating blood flow at postsurgical sites.

Leeches Dosing
Leeches have been traditionally applied as the living animal ad libitum.

Contraindications
Contraindications have not yet been identified.

Pregnancy/Lactation
Information regarding safety and efficacy in pregnancy and lactation is lacking.

Leeches Interactions
None well documented.

Leeches Adverse Reactions
Allergic reactions, anaphylaxis, and infections, possibly with hepatitis and HIV, may develop.

Toxicology
Repeated leeching may decrease hemoglobin levels dramatically; transfusion therapy may be required.

History
The medicinal uses of leeches date back to more than 2 centuries before Christ. The 19th century heralded the widespread use of leeches for “bloodletting,” a practice that grew so quickly that by the 1830s a leech shortage arose in France requiring the importation of more than 40 million Mexican leeches. 1 The last 45 years have seen a resurgence in the use of leeches, particularly as adjuncts in postsurgical wound healing procedures.

THERAPEUTIC USES

Medicinal leeches are used to stimulate the flow of blood at postoperative surgical sites, a procedure that has been claimed to increase the success of tissue transplants, reduction mammoplasty, and the surgical reattachment of amputated extremities.

The application of leeches to the area immediately surrounding the surgical wound temporarily reestablishes venous blood flow, thereby allowing the nutritive perfusion of the wound site by fresh blood. Blood stasis is a major contributor to unsuccessful reconstructive surgery. It is believed that if sufficient blood flow is maintained at the site until permanent adequate natural perfusion is established, the affected tissue has a significantly improved survival rate.

After attaching to the site, leeches secrete compounds that reduce blood viscosity; they also draw from 20 to 50 mL of blood from each bite. The leeches provide the drainage needed to permit decongestion and to preserve tissue viability until normal venous flow is established (about 5 to 7 days after the surgery).

Application method

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.

Patients undergoing leech therapy should be administered a broad-spectrum antibiotic such as an aminoglycoside or third-generation cephalosporin to prevent infection by Aeromonas hydrophilia , which is found in the leech gut. 4 , 5 This is of particular importance considering that wild species are being investigated and that these leeches have been reported to contain a variety of potentially pathogenic bacteria. 6 In 1 study, blood from collected African leeches tested positive for HIV and hepatitis B, and leeches bought in German pharmacies contained up to 11 species of bacteria; viruses and protozoans have been shown to survive for months in the gut of the leech and as such, the leech should be considered a vector for infectious diseases. 7

In practice, the area is washed well and covered by gauze or transparent dressing with a precut 1 cm hole to reveal adhesion site. The leech is then placed near the site. The biting end of the leech is generally the smaller of the 2 ends and moves in a “searching” fashion. 4 If attachment does not occur readily, the leech can be induced by pricking the skin with a pin to draw a drop of blood or the area can be dabbed with a sugar solution. The bite has been described as virtually painless or similar to a mosquito bite. A detailed description of the application technique has been outlined by Abrutyn. 8

One leech is 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. The feeding may suffice the leech for months. Removal of the leech may be hastened by applying solutions of salt, vinegar, a match or a local anesthetic, but the leech should not be forcibly removed. Bleeding from the attachment site usually continues for several hours. 10 Reuse of leeches is discouraged to minimize cross-infection.

Leeches Uses and Pharmacology
Medicinal leeches have an anterior and posterior sucker; within the anterior sucker is a y-shaped mouth with marginal teeth for biting. Following attachment, the leech secretes hirudin, a selective thrombin inhibitor, which enhances bleeding and prevents coagulation.

Hirudin was first described more than a century ago. It has recently been identified as a 65-amino acid peptide with antithrombokinase activity. Therapeutic studies of hirudin have been limited by its low natural yield, but the compound has recently been produced in quantities by recombinant gene techniques. Recombinant hirudin binds very efficiently with thrombin, thus low doses are needed to inhibit venous thrombosis in animals. Extracts from leeches have been marketed as a cream for topical application, but their efficacy is unproven.

In addition to hirudin, leeches secrete a vasodilator, a hyaluronidase, a collagenase and 2 fibrinases (1 disrupts clots, the other atherosclerotic plaque). The compound calin has also been isolated from leeches. By binding to collagen to interfere with the platelet-collagen interaction, this inhibitor of von Willebrand factor causes an antithrombotic effect in vitro and in hamster models. There is conflicting evidence as to whether an anesthetic is secreted.

Postsurgical blood flow
Animal data

The ability of leeches to improve blood flow across congested surgical flaps has been documented using Doppler laser perfusion monitoring in pigs. Within 1 hour of applying leeches, blood flow through the surgical area increased 142% at surface probes and 491% at implanted probes. The average change for untreated control flaps was 6%.

Clinical data

A number of studies have confirmed that the use of medicinal leeches improves venous drainage of wound sites in patients who have undergone reattachment surgery after amputation.

One study, however, found no changes in ipsilateral activated partial thromboplastin or prothrombin times when leeches were applied to an intact hand. 17 These findings suggest that significant systemic or local anticoagulation is not likely to occur and the risk of interference with other therapies may be small.

Other uses

Recombinant hirudin has been used successfully in the treatment of Kasabach-Merritt Syndrome, which leads to loss of circulating platelets and fibrinogen. Paradoxically, low-dose subcutaneous hirudin normalized fibrinogen and platelet activity.

Salivary extracts of the giant leech ( Haementeria ) interfere with the metastatic growth of lung tumors