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).
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 )
Hirudo medicinalis is distributed from Britain and southern Norway to the southern Urals and probably as far as the Altai Mountains, occupying the deciduous arboreal zone.
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).
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
Habitat and Ecology
It occurs in ponds, waters that dry up periodically, floodplain pools and small lakes. Other ecological requirements include abundant hosts (frogs, cattle and horses), silty water bottoms, dense submerged and emergent vegetation and gently sloping banks favourable for laying cocoons.
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).
Life History and Behavior
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).
Molecular Biology and Genetics
Barcode data: Hirudo medicinalis
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.
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Download FASTA File
Statistics of barcoding coverage: Hirudo medicinalis
Public Records: 15
Specimens with Barcodes: 15
Species With Barcodes: 1
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
IUCN Red List Assessment
Red List Category
Red List Criteria
- 1994Indeterminate(Groombridge 1994)
- 1990Indeterminate(IUCN 1990)
- 1988Indeterminate(IUCN Conservation Monitoring Centre 1988)
- 1986Indeterminate(IUCN Conservation Monitoring Centre 1986)
Relevance to Humans and Ecosystems
The medicinal leech is parasitic on humans and is a source of unpleasant emotions for leech victims and bystanders alike (Grzinke, 1974).
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).
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).
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).
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.
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. These leeches can live for up to a year between feeding.
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 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 leeches have been found to secrete saliva containing about 60 different proteins. 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. It is also thought that the saliva contains an anesthetic, as leech bites are generally not painful.
In the past
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.
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. 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. The use of leeches began to become less widespread towards the end of the 19th century.
Medicinal leech therapy made an international comeback in the 1970s in microsurgery, used to stimulate circulation to salvage skin grafts and other tissue threatened by postoperative venous congestion, particularly in finger reattachment and reconstructive surgery of the ear, nose, lip, and eyelid. Other clinical applications of medicinal leech therapy include varicose veins, muscle cramps, thrombophlebitis, and osteoarthritis, among many varied conditions. 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. The most common complication from leech treatment is prolonged bleeding, which can easily be treated, although allergic reactions and bacterial infections may also occur.
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.
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