Medicinal leechLeeches are annelids comprising the subclass Hirudinea. There are freshwater, terrestrial, and marine leeches. Like the Oligochaeta, they share the presence of a clitellum. Like earthworms, leeches are hermaphrodites...
es are any of several
speciesIn biology, a species is:* a taxonomic rank or* a unit at that rank ....
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.
General
morphologyIn biology morphology is the form, structure and configuration of an organism.This includes aspects of the outward appearance as well as the form and structure of the internal parts like bones and organs...
follows that of most other leeches.
Medicinal leechLeeches are annelids comprising the subclass Hirudinea. There are freshwater, terrestrial, and marine leeches. Like the Oligochaeta, they share the presence of a clitellum. Like earthworms, leeches are hermaphrodites...
es are any of several
speciesIn biology, a species is:* a taxonomic rank or* a unit at that rank ....
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
morphologyIn biology morphology is the form, structure and configuration of an organism.This includes aspects of the outward appearance as well as the form and structure of the internal parts like bones and organs...
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
dorsalIn 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
dorsalIn 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 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 (
HirudinHirudin is a naturally occurring peptide in the salivary glands of medicinal leeches that has a blood anticoagulant property...
) and anaesthetics they suck out
bloodBlood is a specialized bodily fluid that delivers necessary substances to the body's cells — such as nutrients and oxygen — and transports 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
hermaphroditeIn a biological context, a hermaphrodite is an animal or plant that has both male and female reproductive organs.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 partners can...
s which reproduce by
sexIn 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 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 water divide of the Ural Mountains, the Ural River, the Caspian Sea, the Caucasus Mountains , and the Black Sea to the southeast...
and into
AsiaAsia is the world's largest and most populous continent, located in the eastern and northern hemispheres. It covers 8.6% of the earth's total surface area and with approximately 4 billion people, it hosts 60% of the world's current human population.Asia is traditionally defined as part of the...
as far as
KazakhstanKazakhstan , officially the Republic of Kazakhstan, is a country situated in Eurasia that is ranked as the ninth largest country in the world. It is also the world's largest landlocked country. Its territory of 2,727,300 km² is greater than Western Europe...
and
UzbekistanUzbekistan, officially the Republic of Uzbekistan , is a doubly landlocked country in Central Asia, formerly part of the Soviet Union...
. 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
horseThe horse is a hoofed mammal, a subspecies of one of seven extant species of the 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
cattleCattle 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
vulnerableA vulnerable species is a species which is likely to become endangered unless the circumstances threatening its survival and reproduction improve...
by the IUCN and European Medicinal Leeches are legally protected through nearly all of their natural range. They are particularly sparsely distributed in
FranceFrance , officially the French Republic , is a country located in Western Europe, with several overseas islands and territories located on other continents. Metropolitan France extends from the Mediterranean Sea to the English Channel and the North Sea, and from the Rhine to the Atlantic Ocean...
and
BelgiumThe Kingdom of Belgium is a country in northwest Europe. It is a founding member of the European Union and hosts its headquarters, as well as those of other major international organizations, including NATO...
, and in the UK there may be as few as 20 remaining isolated populations (all widely scattered), the largest (at
LyddLydd 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 "
humorsHumor theory can refer to:*Theory of humor*Humorism, a theory in ancient Greek and Roman medicine...
" that, according to
GalenAelius Galenus or Claudius Galenus , better known as Galen of Pergamum , was a prominent Greek physician and philosopher and probably the most accomplished medical researcher of the Roman period. His theories dominated and influenced Western medical science for well over a millennium...
, must be kept in balance in order for the human body to function properly. (The four humors of ancient medical philosophy were
bloodBlood is a specialized bodily fluid that delivers necessary substances to the body's cells — such as nutrients and oxygen — and transports waste products away from those same cells....
,
phlegmPhlegm is a sticky fluid secreted by the mucous membranes of humans and other animals. 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...
, black bile, and yellow bile.) Any sickness that caused the subject's skin to become red (e.g.
feverFever is a frequent medical sign that describes an increase in internal body temperature to levels above normal...
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
NicanderNicander 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....
in
ColophonColophon was a city in the region of Lydia in antiquity dating from about the turn of the first millennium-BC. It was likely one the oldest of the twelve Ionian League cities, between Lebedos and Ephesus and its ruins are in the eponymously named modern region of Ionia.The city's name comes from...
. Hirudotherapy, the use of medicinal leech for medical purposes, was later popularised by
Avicenna, known as Abū Alī Sīnā or Ibn Sīnā , and commonly known in English by his Latinized name Avicenna , was a Persian polymath and the foremost physician and philosopher of his time...
in
The Canon of MedicineThe Canon of Medicine is a 14-volume medical encyclopedia written by Islamic scientist and physician Ibn Sīnā...
(1020s). He considered the application of
leechLeeches are annelids comprising the subclass Hirudinea. There are freshwater, terrestrial, and marine leeches. Like the Oligochaeta, they share the presence of a clitellum. Like earthworms, leeches are hermaphrodites...
to be more useful than
cuppingFire cupping or simply cupping is a form of traditional medicine found in many cultures world-wide. It involves placing cups containing reduced air pressure on the skin...
in "letting off the
bloodBlood is a specialized bodily fluid that delivers necessary substances to the body's cells — such as nutrients and oxygen — and transports waste products away from those same cells....
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-BaghdadiAbd-al-latif, Abd-el-latif or Abd-ul-Latif , also known as al-Baghdadi , born in Baghdad, Iraq, was a celebrated physician, historian, Egyptologist and traveller, and one of the most voluminous writers of the Near East in his time.-Biography:An interesting memoir of Abdallatif, written by himself,...
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,
saltA salt, in chemistry, is an ionic compound, and can result from the neutralization reaction of acids and bases. Salts are ionic compounds composed of cations and anions so that the product is electrically neutral...
should be "sprinkled on the affected part of the human body." 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 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
coagulationCoagulation is a complex process by which blood forms clots. It is an important part of hemostasis , 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...
, relieve venous pressure from pooling blood (
venous insufficiency), and in
reconstructive surgeryReconstructive surgery is, in its broadest sense, the use of surgery to restore the form and function of the body.Although plastic surgery and plastic surgeons are involved in many aspects of reconstructive surgery, there are other branches of surgery that also perform reconstructive procedures...
to stimulate circulation in reattachment operations for organs with critical blood flow, such as eye lids, 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
recombinantRecombinant DNA is a form of DNA that does not exist naturally, which is created by combining DNA sequences that would not normally occur together...
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.
External links