Medicinal leech
Encyclopedia
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.
of medcal 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 anticoagulant
s (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.
Medicinal leeches are hermaphrodite
s that reproduce by sex
ual mating, laying eggs in clutches of up to 50 near (but not under) water, and in shaded, humid places.
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 collector
s 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 horse
s 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.
" 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 collector
s and were eventually farmed in large numbers.
The first recorded use of leeches in medicine was in 200 BC 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.
. They provide an effective means to reduce blood coagulation
, to 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 eyelids, fingers, and ears. 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. 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.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
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
The general morphologyMorphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
of medcal 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
Dorsum (biology)
In anatomy, the dorsum is the upper side of animals that typically run, fly, or swim in a horizontal position, and the back side of animals that walk upright. In vertebrates the dorsum contains the backbone. The term dorsal refers to anatomical structures that are either situated toward or grow...
side and a lighter ventral side. The dorsal
Dorsum (biology)
In anatomy, the dorsum is the upper side of animals that typically run, fly, or swim in a horizontal position, and the back side of animals that walk upright. In vertebrates the dorsum contains the backbone. The term dorsal refers to anatomical structures that are either situated toward or grow...
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
Jaw
The jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of...
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 anticoagulant
Anticoagulant
An anticoagulant is a substance that prevents coagulation of blood. A group of pharmaceuticals called anticoagulants can be used in vivo as a medication for thrombotic disorders. Some anticoagulants are used in medical equipment, such as test tubes, blood transfusion bags, and renal dialysis...
s (hirudin
Hirudin
Hirudin is a naturally occurring peptide in the salivary glands of medicinal leeches that has a blood anticoagulant property...
) and anaesthetics, they suck out blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
. 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.
Medicinal leeches are hermaphrodite
Hermaphrodite
In biology, a hermaphrodite is an organism that has reproductive organs normally associated with both male and female sexes.Many taxonomic groups of animals do not have separate sexes. In these groups, hermaphroditism is a normal condition, enabling a form of sexual reproduction in which both...
s that reproduce by sex
Sex
In biology, sex is a process of combining and mixing genetic traits, often resulting in the specialization of organisms into a male or female variety . Sexual reproduction involves combining specialized cells to form offspring that inherit traits from both parents...
ual 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 EuropeEurope
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
and into Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
as far as Kazakhstan
Kazakhstan
Kazakhstan , officially the Republic of Kazakhstan, is a transcontinental country in Central Asia and Eastern Europe. Ranked as the ninth largest country in the world, it is also the world's largest landlocked country; its territory of is greater than Western Europe...
and Uzbekistan
Uzbekistan
Uzbekistan , officially the Republic of Uzbekistan is a doubly landlocked country in Central Asia and one of the six independent Turkic states. It shares borders with Kazakhstan to the west and to the north, Kyrgyzstan and Tajikistan to the east, and Afghanistan and Turkmenistan to the south....
. The preferred habitat for this species is muddy freshwater pools and ditches with plentiful weed growth in temperate climates.
Over-exploitation by leech collector
Leech collector
A leech collector, leech gatherer, or leech finder was a person occupied with procuring medicinal leeches, which were in growing demand in 19th-century Europe. Leeches were used in bloodletting but were not easy for medical practitioners to obtain. The collector would sometimes gather the leeches...
s 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 horse
Horse
The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
s in farming (horses were medicinal leeches' preferred food source) and provision of artificial water supplies for cattle
Cattle
Cattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...
. As a result, this species is now considered vulnerable
Vulnerable species
On 30 January 2010, the IUCN Red List of Threatened Species identified 9694 Vulnerable species, subspecies and varieties, stocks and sub-populations.-References:...
by the IUCN, and European medicinal leeches are legally protected through nearly all of their natural range. They are particularly sparsely distributed in France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
and Belgium
Belgium
Belgium , officially the Kingdom of Belgium, is a federal state in Western Europe. It is a founding member of the European Union and hosts the EU's headquarters, and those of several other major international organisations such as NATO.Belgium is also a member of, or affiliated to, many...
, and in the UK there may be as few as 20 remaining isolated populations (all widely scattered). The largest (at Lydd
Lydd
Lydd is a town in Kent, England, lying on the Romney Marsh. It is one of the larger towns on the Marsh, and the most southerly town in Kent. Actually located on Denge Marsh, Lydd was one of the first sandy islands to form as the bay evolved into what is now called the Romney Marsh...
) 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.
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 "humorsHumorism
Humorism, or humoralism, is a now discredited theory of the makeup and workings of the human body, adopted by Greek and Roman physicians and philosophers, positing that an excess or deficiency of any of four distinct bodily fluids in a person directly influences their temperament and health...
" that, according to Galen
Galen
Aelius Galenus or Claudius Galenus , better known as Galen of Pergamon , was a prominent Roman physician, surgeon and philosopher...
, must be kept in balance for the human body to function properly. (The four humors of ancient medical philosophy were blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
, phlegm
Phlegm
Phlegm is a liquid secreted by the mucous membranes of mammalians. Its definition is limited to the mucus produced by the respiratory system, excluding that from the nasal passages, and particularly that which is expelled by coughing . Phlegm is in essence a water-based gel consisting of...
, black bile, and yellow bile.) Any sickness that caused the subject's skin to become red (e.g. fever
Fever
Fever is a common medical sign characterized by an elevation of temperature above the normal range of due to an increase in the body temperature regulatory set-point. This increase in set-point triggers increased muscle tone and shivering.As a person's temperature increases, there is, in...
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 collector
Leech collector
A leech collector, leech gatherer, or leech finder was a person occupied with procuring medicinal leeches, which were in growing demand in 19th-century Europe. Leeches were used in bloodletting but were not easy for medical practitioners to obtain. The collector would sometimes gather the leeches...
s and were eventually farmed in large numbers.
The first recorded use of leeches in medicine was in 200 BC by the Greek physician Nicander
Nicander
Nicander of Colophon , Greek poet, physician and grammarian, was born at Claros, , near Colophon, where his family held the hereditary priesthood of Apollo. He flourished under Attalus III of Pergamum.He wrote a number of works both in prose and verse, of which two survive complete...
in Colophon. Medical use of leeches was discussed by Avicenna
Avicenna
Abū ʿAlī al-Ḥusayn ibn ʿAbd Allāh ibn Sīnā , commonly known as Ibn Sīnā or by his Latinized name Avicenna, was a Persian polymath, who wrote almost 450 treatises on a wide range of subjects, of which around 240 have survived...
in The Canon of Medicine
The Canon of Medicine
The Canon of Medicine is an encyclopedia of Galenic medicine in five books compiled by Ibn Sīnā and completed in 1025. It presents a clear and organized summary of all the medical knowledge of the time...
(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.
Today
Medicinal leeches are now making a comeback in microsurgeryMicrosurgery
Microsurgery is a general term for surgery requiring an operating microscope. The most obvious developments have been procedures developed to allow anastomosis of successively smaller blood vessels and nerves which have allowed transfer of tissue from one part of the body to another and...
. They provide an effective means to reduce blood coagulation
Coagulation
Coagulation is a complex process by which blood forms clots. It is an important part of hemostasis, the cessation of blood loss from a damaged vessel, wherein a damaged blood vessel wall is covered by a platelet and fibrin-containing clot to stop bleeding and begin repair of the damaged vessel...
, to relieve venous pressure from pooling blood (venous insufficiency), and in reconstructive surgery
Reconstructive surgery
Reconstructive surgery is, in its broadest sense, the use of surgery to restore the form and function of the body, although Maxillo-Facial Surgeons, Plastic Surgeons and Otolaryngologists do reconstructive surgery on faces after trauma and to reconstruct the head and neck after cancer.Other...
to stimulate circulation in reattachment operations for organs with critical blood flow, such as eyelids, fingers, and ears. 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. 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
Hirudin
Hirudin is a naturally occurring peptide in the salivary glands of medicinal leeches that has a blood anticoagulant property...
present in leeches, it is impractical to harvest the substance for widespread medical use. Hirudin (and related substances) are synthesised using recombinant
Recombinant DNA
Recombinant DNA molecules are DNA sequences that result from the use of laboratory methods to bring together genetic material from multiple sources, creating sequences that would not otherwise be found in biological organisms...
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.