European Medical Leech

Horse Leech
a drawing of a Medicinal Leech.
Conservation status
Near Threatened (IUCN 2.3)
Scientific classification
Kingdom:	Animalia
Phylum:	Annelida
Class:	Clitellata
Order:	Hirudinida
Family:	Hirudinidae
Genus:	Hirudo
Species:	H. medicinalis
Binomial name
Hirudo medicinalis (Linnaeus, 1758)

Medicinal leeches are any of several species of leeches, but most commonly Hirudo medicinalis, the European Medical Leech.

Other Hirudo species sometimes used as medicinal leeches include (but are not limited to) Hirudo orientalis, Hirudo troctina and Hirudo verbana. The Asian Medical Leech is Hirudinaria manillensis, and the North American Medical Leech is Macrobdella decora.

Morphology

General morphology follows that of most other leeches. Fully mature adults can be up to 20cm in length and are green, brown or greenish brown with a darker tone on the dorsal side and a lighter ventral side, the dorsal side also has a thin red stripe. These organisms have two suckers, one at each end, called the anterior and posterior sucker. The posterior is mainly used for leverage while the anterior sucker, consisting of the jaw and teeth, is where the feeding takes place. Medicinal leeches have three jaws (tripartite) that look like little saws, and on them are about 100 sharp teeth used to incise the host. The incision leaves a mark which is an inverted Y inside of a circle. After piercing the skin and injecting anti-coagulants (Hirudin) and anaesthetics they suck out blood. Large adults can consume up to ten times their body weight in a single meal, with 5-15 ml being the average volume taken.^[1] These leeches can live for up to a year between feeding.

Medicinal leeches are hermaphrodites which reproduce by sexual mating, laying eggs in clutches of up to 50 near (but not under) water, and in shaded, humid places.

Range and ecology

Their range extends over almost the whole of Europe and into Asia as far as Kazakhstan and Uzbekistan. The preferred habitat for this species is muddy freshwater pools and ditches with plentiful weed growth in temperate climates.

Over-exploitation in the 19th Century has left only scattered populations and reduction in natural habitat though drainage has also contributed to their decline. Another factor has been the replacement of horses in farming (horses were medicinal leeches' preferred food source) and provision of artificial water supplies for cattle. As a result this species is now considered vulnerable by the IUCN and European Medicinal Leeches are legally protected through nearly all of their natural range. They are particularly sparsely distributed in France and Belgium, and in the UK there may be as few as 20 remaining isolated populations (all widely scattered), the largest (at Lydd) is estimated to contain several thousand individuals, 12 of these areas have been designated Sites of Special Scientific Interest. There are small transplanted populations in several countries outside their natural range including the USA.

Medicinal use

In the past

In medieval and early modern medicine, the medicinal leech (Hirudo medicinalis and its congeners Hirudo verbana, Hirudo troctina and Hirudo orientalis) was used to remove blood from a patient as part of a process to "balance" the "humors" that, according to Galen, must be kept in balance in order for the human body to function properly. (The four humors of ancient medical philosophy were blood, phlegm, black bile, and yellow bile.) Any sickness that caused the subject's skin to become red (e.g. fever and inflammation), so the theory went, must have arisen from too much blood in the body. Similarly, any person whose behavior was strident and "sanguine" was thought to be suffering from an excess of blood.

The first recorded use of leeches in medicine was in 200 BC by the Greek physician Nicander in Colophon.^[1] Hirudotherapy, the use of medicinal leech for medical purposes, was later popularised by Avicenna in The Canon of Medicine (1020s). He considered the application of leech to be more useful than cupping in "letting off the blood from deeper parts of the body." He also introduced the use of leech as treatment for skin disease. Leech therapy became a popular method in medieval Europe, namely the leeches from Portugal and France, due to the influence of his Canon. A more modern use for medicinal leech was introduced by Abd-el-latif al-Baghdadi in the 12th century, who wrote that leech could be used for cleaning the tissues after surgical operations. He did, however, understand that there is a risk over using leech, and advised patients that leech need to be cleaned before being used and that the dirt or dust "clinging to a leech should be wiped off" before application. He further writes that after the leech has sucked out the blood, salt should be "sprinkled on the affected part of the human body."^[2] The use of leeches began to become less widespread towards the end of the 19th century.^[1]

Today

Medicinal leeches are now making a comeback in microsurgery. They provide an effective means to reduce blood coagulation, relieve venous pressure from pooling blood (venous insufficiency), and in reconstructive surgery to stimulate circulation in reattachment operations for organs with critical blood flow, such as eye lids, fingers, and ears.^[3][4][5] The therapeutic effect is not from the blood taken in the meal, but from the continued and steady bleeding from the wound left after the leech has detached.^[1] The most common complication from leech treatment is prolonged bleeding, which can easily be treated, although allergic reactions and bacterial infections may also occur.^[1]

Because of the minuscule amounts of hirudin present in leeches, it is impractical to harvest the substance for widespread medical use. Hirudin (and related substances) are synthesised using recombinant techniques. Devices called "mechanical leeches" have been developed which dispense heparin and perform the same function as medicinal leeches, but they are not yet commercially available. ^[6][7][8]

References

1. ^ ^{a b c d e} Wells MD, Manktelow RT, Boyd JB, Bowen V (1993). "The medical leech: an old treatment revisited". Microsurgery 14 (3): 183–6. PMID 8479316. 
2. ^ Nurdeen Deuraseh, "Ahadith of the Prophet on Healing in Three Things (al-Shifa’ fi Thalatha): An Interpretational", Journal of the International Society for the History of Islamic Medicine, 2004 (3): 14-20 [18].
3. ^ Abdelgabar AM, Bhowmick BK (March 2003). "The return of the leech". Int. J. Clin. Pract. 57 (2): 103–5. PMID 12661792. 
4. ^ Ernst E (July 2008). "Born to suck--the return of the leech?". Pain 137 (2): 235–6. doi:10.1016/j.pain.2008.02.016. PMID 18367335. 
5. ^ "Shark-bite surfer gives leeches a go". The Australian. 2009-02-25. http://www.theaustralian.news.com.au/story/0,25197,25103341-5006784,00.html. Retrieved 2009-02-25. 
6. ^ Salleh, Anna. A mechanical medicinal leech? ABC Science Online. 2001-12-14. Retrieved on 2007-07-29.
7. ^ Crystal, Charlotte. Biomedical Engineering Student Invents Mechanical Leech University of Virginia News. 2000-12-14. Retrieved on 2007-07-29.
8. ^ Fox, Maggie. ENT Research Group Recognized for Mechanical Leech Project Otoweb. University of Wisconsin, Madison, Division of Otolaryngology. Retrieved on 2007-07-29.

External links

• Turkey, Medicinal Leeches
• Taxonomy page in Pubmed with many excellent references
• Hirudolab, Clinical information including contra-indication, and worldwide supplier to hospitals and research laboratories.
• Medicinal Leech, Turkey, Supplier of Medicinal Leeches
• Documentary about alternative medicine with leeches and maggots
• Document concerning the history of Bloodletting