Overview

Brief Summary

The taxonomy of what has until recently been considered as a single species, Hirudo medicinalis, has been revised dramatically during the first decade of the 21st century (Trontelj and Utevsky 2012 and references therein). In fact, it appears there are three species of European medicinal leeches and that most commercial and aquaculture specimens actually belong to the Eastern phylogroup of H. verbana, presumably due to the fact that commercial facilities obtain leeches from Russia and Turkey, the major leech exporters (Siddall et al. 2007; Kutschera 2012; Trontelj and Utevsky 2012). True Hirudo medicinalis is the northernmost species among medicinal leeches. It occupies the deciduous arboreal zone from Britain and southern Norway to the southern Urals and probably as far as the Altai Mountains (Trontelj and Utevsky 2012).

Siddall et al. (2007) note that some researchers see therapeutic potential for many protease inhibitors purified from leech saliva, and that, notwithstanding the historical association with quackery, Hirudo medicinalis has been approved by the United States Food and Drug Administration as a prescription medical device (although most leeches being used therapeutically are apparently H. verbana). Whitaker et al. (2012) reviewed available evidence on the efficacy of medicinal leeches in plastic and reconstructive surgery (mainly to prevent venous congestion) and presented what they considered to be current best evidence to guide clinicians. Yantis et al. (2009) provided guidelines for nurses  for the safe and effective use of leeches.The use of leeches is not without risks, such as serious wound infection, but many medical practitioners and researchers believe the benefits often outweigh the risks and that risks can be minimized (e.g., with the use of prophylactic antibiotics).

  • Kutschera, U. 2012. The Hirudo medicinalis species complex. Naturwissenschaften 99(5): 433-434.
  • Siddall, M.E., P. Trontelj, S.Y. Utevsky, M. Nkamany, and K.S. Macdonald III. Diverse molecular data demonstrate that commercially available medicinal leeches are not Hirudo medicinalis. 2007. Proceedings of the Royal Society B 274: 1481-1487.
  • Trontelj, P. and S.Y. Utevsky. 2012. Phylogeny and phylogeography of medicinal leeches (genus Hirudo): Fast dispersal and shallow genetic structure. Molecular Phylogenetics and Evolution 63: 475-485.
  • Whitaker, I.S., O. Oboumarzouk, W.M. Rozen, N. Naderi, S.P. Balasubramanian, E.A. Azzopardi, and M. Kon, M. 2012. The efficacy of medicinal leeches in plastic and reconstructive surgery: A systematic review of 277 reported clinical cases. Microsurgery 32(3): 240-250.
  • Yantis, M.A., K.N. O'Toole, and P. Ring. 2009. Leech Therapy. American Journal of Nursing 109(4): 36-42.
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Description

This animal has a slightly flattened cylindrical body, divided into 33 or 34 segments. The upperside is dark brown or black with six long reddish stripes, whilst the underside is speckled. There is a disc-shaped sucker at the head end. The leech is famous for sucking blood and the 'mouth' of the animal is situated within the sucker, complete with teeth. The leech also has five pairs of eyes.
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Biology

Leeches feed on blood. Having attached itself to the host animal, it pierces the skin and injects an anaesthetic to hide the pain of its bite so that the host does not find the leech and remove it, and an anticoagulant chemical, which prevents the host's blood from clotting whilst the leech feeds. The length of time a leech may feed seems to vary. One surveyor, as an experiment, allowed a leech to feed on him and it fed for 83 minutes. Another, presumably less-hungry individual, fed for just 25 minutes. During a meal, it may extract 15 millilitres of blood, which can increase the size of the leech by anything up to eleven times its normal body dimensions. A leech's meal can sustain it for over six months, but it may also have to wait many months between feeds. During this time, they can digest their own body tissue to avoid starvation. Leeches find their host animals by detecting disturbance in the water, and they can prey on small creatures as well as large. A frog or a newt, for example, can die from excessive blood-loss following an attack by a leech. Leeches may also behave as predators on some species of fish such as sticklebacks, as well as on great-crested newts and marsh frogs. Leeches are often found in the nests of birds such as moorhens, and seem to use them as shelter as well as finding a food source. Dismantling old nests can be a method of surveying for leeches. The eggs are laid in a spongy cocoon on damp ground and, at Dungeness in Kent, they are associated with the roots of willowherb. On nearby Walland Marsh, the eggs have been found in damp turf on close-grazed sheep pasture. Humans are susceptible to parasitism by leeches but, apart from feelings of disgust, most suffer no ill effects. However, medicinal leeches have been used for removing 'bad blood' from human patients for hundreds of years. Although this practice fell into abeyance by the beginning of the 20th century, leeches are once again being used to restore blood circulation following tissue grafts. Leech saliva may also prove helpful in the future, too, as it apparently contains antibiotics as well as anticoagulants that may prove useful in surgery.
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Distribution

Range Description

The medicinal leech has been recorded throughout Europe as far east as the Ural mountain range. It has a patchy distribution.
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Geographic Range

The range extends through parts of western and southern Europe to the Ural mountains and the countries bordering the northeastern Mediterranean (Sawyer, 1986).

Biogeographic Regions: palearctic (Native )

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Range

The medicinal leech has been recorded in 24 countries throughout Europe as far as the Ural mountain range. It is scarce in France and Belgium, and is thought to occur in more than 20 scattered populations in the UK. These extend from Kent to Argyll and Islay in Scotland, and from Norfolk to Anglesey.
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Physical Description

Morphology

Physical Description

The medicinal leech has a cylindrical, dorsoventrally flattened body divided into thirty-three or thirty-four segments. The dorsal side is dark brown to black, bearing six longitudinal, reddish or brown stripes, and the ventral surface is speckled. All members bear a posterior and anterior disk-shaped sucker. The anterior sucker surrounds the oral opening where the teeth for incison are located. In addition, the medicinal leech has five pairs of eyes located on its front end. H. medicinalis has several pairs of testes and one pair of ovaries as well as a thickening of the body ring, known as a clitellum, which is visible during the breeding season (Grzimek, 1974).

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Ecology

Habitat

Habitat and Ecology

Habitat and Ecology
Found in naturally occurring freshwater lakes, ponds, streams, and marshes. Usually rests at air/water interface near the shore.

Has been used medicinally for the purpose of phlebotomy (drawing blood) for millennia, and was popularized for this use in the nineteenth century. Currently used in microsurgery to reduce postoperative haematomas is quite effective. The species is commercially available for medical purposes. Several anticoagulants, such as the antithrombin compound hirudin, have been extracted from salivary tissues and have biomedical/pharmacological use.

Systems
  • Terrestrial
  • Freshwater
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The medicinal leech is amphibious, needing both land and water, and resides exclusively in fresh water. A typical habitat for H. medicinalis would be a small pond with a muddy bottom edged with reeds and in which frogs are at least seasonally abundant (Sawyer, 1986).

Aquatic Biomes: lakes and ponds

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The leech is an amphibious freshwater animal, and usually found in small pools with muddy bottoms and fringed with reeds. These pools are also shared with frogs, toads or newts for at least some of the year. Leeches prefer water that is eutrophic, meaning it is high in nutrients. Where amphibians are not present in leech infested ponds, it is believed that grazing stock provide the food source. On Romney Marsh in Kent, there are extensive populations of the medicinal leech living in the shallow parts of deep gravel pits, and in ditches that run through the grazing marshes. In Cumbria, leeches have been found in conditions that differ markedly from those in Kent. Here, it is thought that being shallower, the water warms up quickly to about 20°C, a temperature that must be attained for at least part of the year in order for leeches to survive in a pond.
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Trophic Strategy

Food Habits

Hirudo medicinalis is parasitic and the adults feed on the blood of mammals. It attaches to the host by means of its two suckers and bites through the skin of its victim. Simultaneously, the leech injects an anaesthetic so that its presence is not detected, and an anticoagulant in order for the incision to remain open during the meal. It has three jaws, which work back and forth during the feeding process, which ususally lasts about 20 to 40 minutes and leaves a tripartite star-shaped scar on the host. After a full meal of 10ml to 15 ml of blood, the medicinal leech may increase 8 to 11 times its initial body size. Leeches only feed about once every six months, this is about how long the blood meal takes to be fully digested. Certain bacteria keep the blood from decaying during the long digestion period. H. medicinalis may even go longer than six months without food by digesting its own tissues.

Young leeches feed on frogs instead of mammals because their jaws are not yet strong enough to cut through mammalian skin (Grzimek, 1974; Sawyer, 1986).

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Life History and Behavior

Reproduction

H. medicinalis breeds once during an annual season that spans June through August. It also remains fertile over a period of years,unlike most other leech species. The act of copulation takes place on land, where one leech attaches ventrally to one another by means of a mucus secretion. All leeches are hermaphroditic and fertilization is internal. Sperm is injected into the vagina by an extendable copulatory organ. A cocoon is formed around the clitellum and slips off the anterior section of the leech. The whole egg sac is laid in damp soil usually just above the shoreline. After about 14 days, the eggs hatch as fully formed miniature adults (Grzimek, 1974; Sawyer 1986).

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Molecular Biology and Genetics

Molecular Biology

Barcode data: Hirudo medicinalis

The following is a representative barcode sequence, the centroid of all available sequences for this species.


There are 15 barcode sequences available from BOLD and GenBank.  Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.  See the BOLD taxonomy browser for more complete information about this specimen and other sequences.

ATTGGAACATTATATCTTATTCTTGGTTCTTGATCAGCTATATTAGGTTCTTCTATAAGATCA---ATTATTCGAATTGAATTGGCACAACCTGGAAAGTTTTTGGGTGAT---GATCAACTATACAATTCTTTAGTAACTGCTCATGGATTAGTAATAATTTTCTTTATAGTAATACCAATTTTAATTGGTGGCTTTGGAAATTGACTTTTGCCATTAATA---GTTGGTGCTATTGATATATCATTTCCCCGATTAAATAATTTTAGATTTTGGTTATTACCACCTTCAATAATTATATTATTAAGTTCATCAATAATCGAAAATGGGGTAGGTACAGGATGAACCCTTTATCCTCCTCTAGCAGATAGTATTTCTCATTCAGGCCCATCTGTAGATATG---GCTATTTTTTCATTACATATAGCTGGGGCGTCATCAATTCTTGGATCTTTAAATTTTATTTCAACTATTATTAATATACGTATTTCTGGAATAAGATCTGAACGAGTTCCGCTATTTGTATGATCAGTAGTAATTACTACTATTTTATTGCTTCTTTCATTACCAGTATTAGCTGCA---GCTATTACAATATTATTAACTGATCGTAATTTAAATACTACTTTTTTTGATCCAATTGGAGGAGGGGATCCAGTCTTATTTCAACATCTATTTTGGTTCTTTGGTCATCCAGAGGTTTATATTTTAATTTTACCTGGGTTTGGTGCTATTTCTCATATTGTCTCTAATGGCTCTAAAAAAATT---GAACCTTTTGGTGCATTAGGTATAATCTATGCAATAATTGGGATTGCTATTTTAGGGTTTATTGTATGAGCTCATCATATATTTACAGTTGGATTAGATGTAGATACTCGTGCGTATTTTACTGCTGCTACTATAGTTATTGCAGTTCCTACTGGAATCAAAGTATTTAGTTGACTA---GCTACA
-- end --

Download FASTA File
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Statistics of barcoding coverage: Hirudo medicinalis

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 15
Specimens with Barcodes: 15
Species With Barcodes: 1
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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
LR/nt
Lower Risk/near threatened

Red List Criteria

Version
2.3

Year Assessed
1996
  • Needs updating

Assessor/s
World Conservation Monitoring Centre

Reviewer/s

Contributor/s

History
  • 1994
    Indeterminate
    (Groombridge 1994)
  • 1990
    Indeterminate
    (IUCN 1990)
  • 1988
    Indeterminate
    (IUCN Conservation Monitoring Centre 1988)
  • 1986
    Indeterminate
    (IUCN Conservation Monitoring Centre 1986)
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The medicinal leech is rare throughout its range in Europe and extinct in much of its former range. This is due primarily to the overharvesting of leeches in the past century for medicinal use. Other factors contributing to the leech's reduced status is the alteration of its usual habitat and possibly a decrease in the frog population. Frogs are essential for leech development as its young cannot yet feed off mammals for its first two meals (Sawyer, 1986).

US Federal List: no special status

CITES: appendix ii

IUCN Red List of Threatened Species: lower risk - near threatened

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Status

Classified as Vulnerable in the UK, listed under Appendix III of the Bern Convention, Appendix II of the Convention on International Trade in Endangered Species (CITES), Annex V of the Habitats Directive, and protected in the UK under Schedule 5 of the Wildlife and Countryside Act, as amended.
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Population

Population
It is scarce in France and Belgium, and is thought to occur in more than 20 scattered subpopulations in the UK.

Population Trend
Unknown
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Threats

Major Threats
The medical use of leeches might explain their wide distribution across Europe, as they are thought to have been released into ponds once they had been used for bleeding patients. It is also thought that in the past over-collecting reduced their numbers in some areas. Over-collecting for medical purposes is unlikely to be a threat today, given the protected nature of this species and the ability to breed leeches commercially at leech farms. Perhaps a more significant issue is the conversion of grazing marshes (the prime habitat of the species) to arable cultivation - resulting in lowering of water levels, pollution, and fewer host species. Invasion of scrub around ponds has also been a problem in places.
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Curiously, the medical use of leeches might explain their wide distribution across the country, as they are thought to have been released into ponds once they had been used for bleeding patients. It is also thought that over-collecting reduced their numbers in some areas. Over-collecting for medical purposes is unlikely to be a threat these days, given the protected nature of this species and the ability to breed leeches commercially at leech farms. Conversely, the pharmaceutical industry has funded much of the recent work under the UK Species Action Plan for this leech. In Romney Marsh perhaps the most significant issue has been the conversion of grazing marsh to arable cultivation - resulting in lowering of water levels, pollution, and fewer host species. Invasion of scrub around ponds has also been a problem.
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Management

Conservation Actions

Conservation Actions
Listed under Appendix III of the Bern Convention, Appendix II of the Convention on International Trade in Endangered Species (CITES), Annex V of the Habitats Directive.
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Conservation

The medicinal leech is listed in the UK Biodiversity Action Plans (UK BAP), and is included in English Nature's Species Recovery Programme. As a first step in ensuring its survival as a native species, many of the leech's known sites were designated as Sites of Special Scientific Interest (SSSIs), and a survey was commissioned to establish the species' true status. An obvious requirement of any species of animal is a food source, and for the medicinal leech this source is other animals. The diet of leeches on Romney Marsh is not perfectly understood. Birds and frogs do seem to be major prey items, but fish have been attacked, and it is suspected that mammals are an under-recorded food item. There are several reports of them feeding on sheep. Scrub clearance around the shallow ponds on Romney Marsh has resulted in leeches taking up residence, and they have also colonised a large number of gravel pits on Dungeness originally created for bird conservation. At the site in Kent, which has the UK's largest leech population and is within the RSPB reserve at Dungeness, water birds provide the food source. At another site, Moccas Park lake in Herefordshire, grazing animals use the lake as a source of drinking water, which suits the leech very well.
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Relevance to Humans and Ecosystems

Benefits

Economic Importance for Humans: Negative

The medicinal leech is parasitic on humans and is a source of unpleasant emotions for leech victims and bystanders alike (Grzinke, 1974).

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Economic Importance for Humans: Positive

The medicinal leech, as its name suggests, has historically been used for medicinal purposes, mainly to remove "bad blood" from the diseased. Around 1850 this practice fell into disrepute, but H. medicinalis is again becoming of value in medicinal practices. Today this species is used to relieve pressure and restore circulation in tissue grafts where blood accumulation is likely such as severed fingers and ears. The anticoagulant of leeches is also a fertile ground of research for surgeries in which an incision must be kept open. In addition, leech saliva is found to contain powerful antibiotics and anaesthetics which no doubt will prove useful in future medicinal practice (Sawyer, 1986).

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The medicinal leech (Hirudo medicinalis) has been used during medical surgery to minimize blood buildup. Due to anticoagulant properties in its saliva, this leech has been very useful for this purpose. Medicinal leeches have been important in research for neurobiology, developmental genetics, enteric symbioses, or oncology (Siddall et al. 2007). There have been at least 115 bioactive compounds isolated from medicinal leeches, includin anticoagulants, antistasins, and other protease inhibitors (Siddall et al. 2007), however it appears that these bioactive compounds are not limited to just Hirudo medicinalis but are also found in additional species of European medicinal leeches (Siddall et al. 2007). Many bioreactive compounds isolated from medicinal leeches are still being researched for their potential; further research will show whether the antimetastatic properties of Hirustasin (isolated from medicinal leeches) are without anticoagulant effects that hinder their use in cancer patients (Sollner et al. 1994).

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Risks

Hirudo medicinalis is a parasitic organism and in various circulmstances, it can negatively affect ecosystems and their inhabitants. It feeds on the blood of vertebrates, especially mammals whose blood holds higher energy content compared to amphibians (Merila and Sterner 2002). In addition to mammals, leeches can also parasitize amphibians (e.g., frogs, toads, and newts) and negatively affect their population dynamics by reducing reproductive success furing the breeding season (Merila and Sterner 2002).

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Wikipedia

Hirudo medicinalis

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

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

Morphology[edit]

The general morphology of medicinal leeches follows that of most other leeches. Fully mature adults can be up to 20 cm 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 suckers. The posterior is used mainly for leverage, whereas 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 that is an inverted Y inside of a circle. After piercing the skin and injecting anticoagulants (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.[2] These leeches can live for up to a year between feeding.

Medicinal leeches are hermaphrodites that 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[edit]

Typical habitat with a large population of Hirudo medicinalis, in Germany

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 by leech collectors 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 near threatened 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[edit]

Beneficial secretions[edit]

Medicinal leeches have been found to secrete saliva containing about 60 different proteins.[3] These achieve a wide variety of goals useful to the leech as it feeds, helping to keep the blood in liquid form and increasing blood flow in the affected area. Several of these secreted proteins serve as anticoagulants (such as hirudin), platelet aggregation inhibitors (most notably apyrase, collagenase, and calin), vasodilators, and proteinase inhibitors.[4] It is also thought that the saliva contains an anesthetic,[5] as leech bites are generally not painful.

In the past[edit]

A caricature of a physician prescribing leeches for a weak, bedbound woman

The first description of leech therapy, classified as blood letting, was found in the text of Sushruta samhita (dating 800 B.C.) written by Sushruta, who was also considered the father of plastic surgery. He described 12 types of leeches (6 poisonous and 6 non-poisonous). Diseases where leech therapy was indicated were skin diseases, sciatica, and musculoskeletal pains.

Earthenware jar for holding medicinal leeches

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 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. Leeches were often gathered by leech collectors and were eventually farmed in large numbers.

A recorded use of leeches in medicine was also found during 200 B.C. by the Greek physician Nicander in Colophon.[2] Medical use of leeches was discussed by Avicenna in The Canon of Medicine (1020s), and by Abd-el-latif al-Baghdadi in the 12th century.[citation needed] The use of leeches began to become less widespread towards the end of the 19th century.[2]

Today[edit]

Medicinal leech therapy made an international comeback in the 1970s in microsurgery,[6][7] used to stimulate circulation to salvage skin grafts and other tissue threatened by postoperative venous congestion,[6][8] particularly in finger reattachment and reconstructive surgery of the ear, nose, lip, and eyelid.[7][9] Other clinical applications of medicinal leech therapy include varicose veins, muscle cramps, thrombophlebitis, and osteoarthritis, among many varied conditions.[10] 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, as well as the anesthetizing, anti-inflammatory, and vasodilating properties of the secreted leech saliva.[2] The most common complication from leech treatment is prolonged bleeding, which can easily be treated, although allergic reactions and bacterial infections may also occur.[2]

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" that dispense heparin and perform the same function as medicinal leeches have been developed, but they are not yet commercially available.[11][12][13]

See also[edit]

References[edit]

  1. ^ World Conservation Monitoring Centre (1996). "Hirudo medicinalis". IUCN Red List of Threatened Species. Version 2009.2. International Union for Conservation of Nature. Retrieved April 24, 2010. 
  2. ^ 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. doi:10.1002/micr.1920140309. PMID 8479316. 
  3. ^ Baskova, I.P.; Zavalova, Basanova, Moshkovskii, Zgoda (Nov 2004). "Protein Profiling of the Medicinal Leech Salivary Gland Secretion by Proteomic Analytical Methods". Biochemistry 69 (7): 770–775. doi:10.1023/b:biry.0000040202.21965.2a. 
  4. ^ "Biology". Sangues Medicinales. Ricarimpex. Retrieved 26 November 2012. 
  5. ^ Mory, Robert N.; Mindell, David; Bloom, David A. (1 July 2000). "The Leech and the Physician: Biology, Etymology, and Medical Practice with Hirudinea medicinalis". World Journal of Surgery 24 (7): 878–883. doi:10.1007/s002680010141. Retrieved 11 December 2012. 
  6. ^ a b Wittke-Michalsen, E (14 March 2007). "2: The History of Leech Therapy". In Michaelsen, A; Roth, M; Dobos, Gustav. Medicinal Leech Therapy. Thieme. pp. 4–12. ISBN 978-3-13-161891-7. Retrieved 18 December 2013. 
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