Records indicate that use of the medicinal leech, Hirudo medicinalis, dates back to ancient Egypt and Greece and became popular during the Middle Ages, when it was the main method of medicinal blood-letting or “purification”. Blood-letting was at that time prescribed to treat a variety of conditions from headaches to fevers. Britain used over 42 million leeches a year in Victorian times for medicinal blood-letting, creating an industry worth £1m per annum at 19th century prices. However, enthusiasm for this practice died out in the late 1800s when the benefits of blood-letting were increasingly called into question.
Leeches can be used to relieve vascular congestion caused by poor venous drainage in vascularly compromised tissue. This article describes how the treatment works and some practical considerations.
Hirudotherapy then re-emerged in the 1970s as an adjunct to plastic, reconstructive and trauma surgery. The development of microsurgery made it possible for surgeons to reattach severed blood vessels after traumatic amputation and transplant skin flaps. However, venous congestion and poor drainage of blood from tissue often caused these procedures to fail. Without relief of congestion, blood clots form and prevent blood flow to the reattached tissue, leading to tissue death. Leeches remove blood from tissue before it can clot, preventing venous congestion. This keeps tissue healthy and perfused until new veins can grow to sustain venous return — a process that takes five to six days.
Contemporary leech therapy is now used to treat poor venous drainage, relieve vascularly compromised flaps and salvage tissue that has been surgically reattached following traumatic amputation. The success of leech therapy has been estimated at 78%, with an overall complication rate of 21.8%.
Hirudo medicinalis are abundant in the freshwater systems of Europe and North America. They are segmented worms without exoskeletons and can grow to be 12cm long, contracting to around a third of that length when resting. They have suckers at both ends that are used to attach to tissue when feeding. At the anterior end is the mouth, which has over 300 teeth in three sets of jaws. These latch onto their host leaving a Y-shaped bite. Feeding is stimulated by proximity of mammalian body temperatures and detection of sodium and arginine in blood. When a leech is attached to a host, it will ingest around 5–15ml of blood — up to 10 times its body weight — in approximately 10–60 minutes before detaching itself.
Leech saliva contains a number of different substances, including hirudin, calin, anaesthetic compounds and antihistamine vasodilators. Hirudin is a potent anticoagulant that inhibits the conversion of fibrinogen to fibrin — preventing blood from clotting. Hirudin works with vasodilator compounds to increase blood flow to an area; at the same time the anaesthetic compounds allow for painless attachment.
When feeding, the leech also injects calin, which binds to collagen and neutralises its capacity to induce clotting. This produces a prolonged anticoagulant effect of up to 10 hours.
Sourcing and storing leeches
Few companies provide leeches for medicinal use in the UK. The biggest supplier is Swansea-based company Biopharm, which ships around 60,000 leeches a year to hospitals throughout Europe.
Leeches should be cared for according to the instructions provided by the supplier. They are usually shipped in water using a specialised container and kept at a temperature of 4–5C. Gel may be used instead of water to transport them, but this should be for short-term use only (two days maximum).
When storing leeches it is important to place them in a clean glass or plastic container with plenty of distilled, non-chlorinated or bottled water; tap water should never be used. The supplier will recommend a commercially available salt additive.
Leeches should be stored in a refrigerator or cool dark place before being used. Temperatures above 20C should be avoided and leeches should never be placed in direct sunlight. A perforated container lid is essential to prevent escape, but because a leech’s body can be remarkably elastic the perforations in the lid must be extremely small.
After use, leeches should be destroyed by immersing them in a solution of 7% ethanol for five minutes, before euthanasing them with 70% ethanol. They should be disposed of as biohazardous waste. Leeches must never be reused, even on the same patient.
Before prescribing hirudotherapy, the congested tissue must be examined to ensure that venous congestion, and not arterial insufficiency, is present. Medicines that increase the risk of bleeding or reduce immune response should be reviewed and patients must avoid caffeine until therapy is completed to reduce the risk of vasoconstriction. Smoking and using nicotine replacement products are contraindicated during therapy because of the vasoconstrictive effects of carbon monoxide and nicotine. (The box below lists other contraindications to leech treatment.) A blood transfusion protocol should also be in place before therapy starts.
Leech therapy should not be used in the following circumstances:
- Arterial insufficiency
- Previous allergic reaction to leeches
- Unstable medical status
- Immunosuppression (eg, HIV infection, concurrent chemotherapy)
- If the patient refuses to accept a blood transfusion should one be needed (eg, on religious grounds)
- If the patient refuses to consent to leech therapy
Before applying a leech, the skin should be washed with soap and rinsed with sterile water. Many protocols stipulate that gauzes soaked in heparin 100 units/ml be used on the skin to prevent clotting and promote free bleeding. Residue should be wiped away before the leech is applied because heparin will repel it.
Wearing non-sterile gloves, the practitioner uses a pair of long non-toothed forceps to extract a single leech from the container. This is easier to do immediately after taking the container out of the refrigerator when the leeches are relatively docile. The leech is then placed into a 5cc plastic syringe (with the plunger removed), which is inverted over the wound site. The syringe can be removed when the leech begins to feed. To prevent leech relocation, and to reassure the patient, dampened gauze can be used to restrict movement.
If the leech will not attach, pricking the skin to produce a blood droplet will usually encourage attachment. Once attached, the leech will feed for approximately 45 minutes before detaching. If the leech is reluctant to detach, 5% topical cocaine can be used to paralyse it. Forcible removal with forceps is never indicated. Persistent reluctance of a leech to attach or detach is indicative of dying tissue or poor arterial supply.
After therapy, a leech bite will bleed for around ten hours. During this time, the skin should be washed regularly to remove formative blood clots. Many protocols use heparin washes to prolong bleeding.
The vital signs of the patient should be monitored regularly and full blood counts measured daily. Patients who receive treatment over several days and those who have large areas of skin affected may require blood transfusions.
Regular observation of the treatment site is mandatory; colour and appearance of the tissue, presence of pulses and clinical response should be recorded.
Leeches have an obligate symbiotic relationship with Aeromonas hydrophilia, a bacterium present in the gut of the leech that plays a major role in the digestion and stasis of blood. The presence of these bacteria may cause or complicate local or systemic infections and this should be considered before therapy is started. Around a fifth of patients will develop infective complications if they do not receive prophylactic antibiotics.
A hydrophilia is usually sensitive to second- and third-generation cephalosporins, chloramphenicol, aminoglycosides, fluoroquinolones and trimethoprim. The bacterium produces beta-lactamase; therefore penicillins and first-generation cephalosporins are ineffective against this bacterium.
Studying this article will help you gain a better understanding of:
- The historic development of hirudotherapy
- The medical use of leeches
- How leeches are handled before, during and after therapy
- How are leeches ordered, stored and used in your trust?
- What counselling points should patients be given when receiving leech therapy?
- What are the ethics of using living creatures for therapeutic purposes?
Citation: Clinical Pharmacist DOI: 10.1211/CP.2014.11136626