Difference between revisions of "Leech" - New World Encyclopedia

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{{Taxobox
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| color = pink
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| name = Leeches
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| image = Leech blutegel.jpg
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| image_width = 250px
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| image_caption = A Leech on stones
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| regnum = [[Animal]]ia
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| phylum = [[Annelida]]
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| classis = [[Clitellata]]
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| genus = [[Macrobdella]]
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| subclassis = '''Hirudinea'''
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| subclassis_authority = [[Jean-Baptiste Lamarck|Lamarck]], 1818
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| subdivision_ranks = Orders
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| subdivision = [[Arhynchobdellida]] or [[Rhynchobdellida]]<br/>
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There is some dispute as to whether Hirudinea should be a class itself, or a subclass of the Clitellata.
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}}
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'''Leeches''' are [[annelid]]s comprising the subclass ''Hirudinea''. There are fresh
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water, terrestrial and marine leeches.  Like their near relatives, the [[Oligochaeta]], they share the presence of a [[clitellum]]. Like earthworms, leeches are [[hermaphrodite]]s.  The [[medicinal leech]], ''Hirudo medicinalis'', which is native to Europe, and its [[congener]]s have been used for clinical [[bloodletting]] for thousands of years.
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All leech species are [[carnivorous]].  Some are [[predatory]], feeding on a variety of invertebrates such as worms, snails, insect larvae, crustaceans, while a very few are [[haemophagic]] [[Parasitism|parasitic]] blood-sucking leeches, feeding on the blood of vertebrates such as amphibians, reptiles, waterfowl, fish, and mammals (including humans). The most important predators of leeches are fish, [[aquatic insects]], [[crayfish]] and other leeches specialized for predation on leeches.
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Haemophagic leeches attach to their hosts and remain there until they become full, at which point they fall off to digest. Leeches' bodies are composed of 34 segments. They all have an anterior (oral) sucker formed from the first six segments of their body, which is used to connect to a host for feeding, and can also release an anesthetic  to prevent the host from noticing the leech. They use a combination of mucus and suction (caused by concentric muscles in those six segments) to stay attached and secrete an anti-clotting enzyme into the host's [[Blood|blood stream]]. 
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Some species of leech will nurture their young, providing food, transport, and protection, which is unusual behavior in an invertebrate.
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==Notes on annelids from NWE article on annelids==
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The '''annelids''' (from [[Latin]] ''anellus'' "little ring") are a large [[taxonomy|phylum]] ('''Annelida''') of [[invertebrate]] [[animal]]s, comprising the segmented [[worm]]s, including the well-known [[earthworm]]s and [[leech]]es. There are about 15,000 known modern species of annelids.
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Annelids are found in most wet environments and include many terrestrial, freshwater, and especially marine species (such as the [[polychaete]]s), as well as some which are [[parasite|parasitic]] or [[symbiosis|mutualistic]]. They range in length from under a millimeter to over three meters (the seep tube worm ''Lamellibrachia luymesi'').
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In addition to enhancing the [[biodiversity|diversity]] of nature, which brings so much joy to [[human]]s, the segmented worms are [[ecology|ecologically]] and [[medicine|medically]] important. They are common in marine, freshwater, and terrestrial environments, serving as part of the food chain, and helping to turn over the soil and sediments. Some segmented worms have commercial use as bait for sport fishing or food for tropical aquarium fish. The leech can be used medically, for example, in controlling swelling, as it produces chemicals that can serve as an anesthetic and prevent [[blood]] coagulation.
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=== Classes and subclasses of annelida ===
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The three major groups of annelids are the polychaetes (largely marine annelids, with over 5,500 species); the oligochaetes ([[earthworm]]s and freshwater worms, with over 3,000 species); and the hirundinea ([[leech]]es, with about 500 species). However, biological classification of annelids can vary widely among [[taxonomy|taxonomists]].
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Some consider there to be three classes of annelids: ''Polychaeta'', ''Clitellata'', and ''Aelosomata''. The Clitellata are then further divided into three or four subclasses: ''Oligochaeta'' (earthworms and freshwater worms), ''Hirundinea'' (leeches), and ''Branchiobdella'' (about 150 species of small animals that are largely parasites or commensals on crayfish), and sometimes ''Acanthobdellida'' (leech-like, temporary parasite, which is also placed in Hirundinea in some classifications). Aelosomata includes small to very small annelides, with about 25 known species. This taxonomy looks like the following:
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::Class [[Polychaeta]] <br/>
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::Class Aelosomata <br/>
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::Class Clitellata<br/>
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::  Oligochaeta - earthworms and so forth<br/>
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::  Branchiobdellida — small, largely parasites or commensuals<br/>
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::  Hirudinea - [[leech]]es<br/>
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::  Acanthobdellida (sometimes part of Hirudinea)<br/>
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Another taxonomic scheme regards two groups of polychaetes—the ''Archiannelida'' and the ''Myzostomaria''—as classes in their own right, and recognizes four total classes: Polychaeta, Clitellata, Myzostomida, and Archiannelida. This looks like the following:
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::Class [[Polychaeta]] <br/>
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::Class Clitellata<br/>
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::  Oligochaeta<br/>
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::  Branchiobdellida<br/>
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::  Hirudinea<br/>
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::Class [[Myzostomida]]*<br/>
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::Class [[Archiannelida]]*<br/>
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In some biological classifications, the ''Clitellata'' is considered a subphylum and the ''Oligochaeta, Hirudinea'' and ''Branchiobdellida'' are treated as classes of this subphylusm.
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A simple classification scheme is to recognize two classes of annelids, the ''Polychaeta'' and the ''Clitellata:''
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::*''Clitellata''
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::**''Oligochaeta'' - The class ''Oligochaeta'' includes the megadriles (earthworms), which are both aquatic and terrestrial, and the microdrile families such as tubificids, which include many marine members as well.
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::**[[Leech]]es ''(Hirudinea)'' - These include both bloodsucking external parasites and predators of small invertebrates. 
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::*[[Polychaeta]] - This is the largest group of annelids and the majority are marine. All segments are identical, each with a pair of parapodia. The parapodia are used for swimming, burrowing, and the creation of a feeding current.
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There have also been proposals to consider the'' Clitellata'' as part of the ''Polychaeta,'' thus making the latter term synonymous with the annelids.
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=== Anatomy ===
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Annelids are triploblastic protostomes with a coelom (at least historically), closed circulatory system, and true segmentation. ''Protosomes'' are animals with bilaterial symmetry where the first opening in development, the blastophore, becomes its mouth. ''Triploblastic'' means that they have three primary tissue areas formed during embryogenesis. A ''coelom'' is a fluid-filled body cavity.
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[[Image:Libr0409.jpg|200px|right|thumb|[[Polychaeta]]: "A variety of marine worms" plate from ''Das Meer'' by M. J. Schleiden (1804–1881)]]
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Oligochaetes and polychaetes typically have spacious coeloms; in leeches, the coelom is largely filled in with tissue and reduced to a system of narrow canals; archiannelids may lack the coelom entirely. The coelom is divided into a sequence of compartments by walls called ''septa''. In the most general forms, each compartment corresponds to a single segment of the body, which also includes a portion of the nervous and (closed) circulatory systems, allowing it to function relatively independently. Each segment is marked externally by one or more rings, called ''annuli''. Each segment also has an outer layer of circular [[muscle]] underneath a thin cuticle and [[epidermis]], and a system of longitudinal muscles. In earthworms, the longitudinal muscles are strengthened by collagenous lamellae; the leeches have a double layer of muscles between the outer circulars and inner longitudinals. In most forms, they also carry a varying number of bristles, called ''setae'', and among the polychaetes a pair of appendages, called ''parapodia''.
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Anterior to the true segments lies the prostomium and peristomium, which carries the [[mouth]], and posterior to them lies the pygidium, where the [[anus]] is located. The digestive tract is quite variable but is usually specialized. For example, in some groups (notably most earthworms) it has a typhlosole (internal fold of the intestine or intestine inner wall), to increase surface area, along much of its length. 
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Different species of annelids have a wide variety of diets, including active and passive hunters, scavengers, filter feeders, direct deposit feeders that simply ingest the sediments, and blood-suckers.
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The [[vascular system]] and the [[nervous system]] are separate from the digestive tract. The vascular system includes a dorsal vessel conveying the blood toward the front of the worm, and a ventral longitudinal vessel that conveys the blood in the opposite direction. The two systems are connected by a vascular sinus and by lateral vessels of various kinds, including in the true earthworms, capillaries on the body wall.
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The nervous system has a solid, ventral nerve cord from which lateral [[nerve]]s arise in each segment. Every segment has an autonomy; however, they unite to perform as a single body for functions such as locomotion. Growth in many groups occurs by replication of individual segmental units; in others, the number of segments is fixed in early development.
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==Phylogeny==
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The leeches are presumed to have evolved from the [[Oligochaeta]], most of which feed on [[detritus (biology)|detritus]].  However, some species in the [[Lumbriculidae]] are predaceous and have similar adaptations to the leeches.
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True leeches, of the subclass [[Euhirudinea]], with both anterior and posterior suckers, are divided into two groups:
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# Rhynchobdellae: "jawless" leeches, armed with a muscular straw-like proboscis puncturing organ in a retractable sheath. The Rhynchobdellae consist of two families: The Glossiphoniidae (flattened leeches with a poorly defined anterior sucker) and the Piscicolidae (have cylindrical bodies and a usually well-marked, bell-shaped, anterior sucker). The Glossiphoniidae live in [[Fresh water|fresh-water]] habitats; the Pisciolidae are found in sea-water habitats.
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# Arhynchobdellids: Leeches which lack a proboscis and which may or may not have jaws armed with teeth. Arhynchobdellids are divided into two orders: [[Gnathobdellid|Gnathobdellae]] and Pharyngobdellae
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## Gnathobdellae: In this order of "jawed" leeches, armed with teeth, is found the quintessential leech: the European medical (bloodsucking) leech, ''Hirudo medicinalis''. It has a tripartite jaw filled with hundreds of tiny sharp teeth. The incision mark left on the skin by the European medical leech is an inverted Y inside a circle. Its North American counterpart is Macrobdella decora, a much less efficient medical leech. Within this order, the family Hirudidae is characterized by aquatic leeches and the family Haemadipsidae by terrestrial leeches. In the latter are Haemadipsa sylvestris, the Indian leech and [[Haemadipsa zeylanica]] (Yamabiru), the Japanese Mountain or Land leech.<ref> http://www.youtube.com/watch?v=ye4N2ZeJESA Video Japanese Mountain leech</ref>
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## Pharyngobdellae: These so called worm-leeches consist of freshwater or amphibious leeches that have lost the ability to penetrate a host's tissue and suck blood. They are carnivorous and equipped with a relatively large, toothless, mouth to ingest worms or insect larvae, which are swallowed whole.
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The Pharyngobdellae have six to eight pairs of eyes, as compared with five pairs in Gnathobdelliform leeches, and include three related families. The Erpobdellidae are some species from freshwater habitats.
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==Use of ''Hirudo medicinalis'' in medicine==
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The leech has long been used in medicine, previously being used to remove poison from the human body, although today its use is mainly limited in limb reattachment procedures instead of the wide-ranging medical use in the past. Leeches have proven highly effective at preventing [[venous]] [[congestion]] after the surgical re-attachment of [[fingers]], [[toes]], [[ears]] and other parts of the body. The word ''leech'' either comes directly from or was influenced by the [[Old English language|Old English]] word for "physician", {{Unicode|''lǣce''}}, which is related to [[Old High German]] ''lāhhi'' and [[Old Irish language|Old Irish]] ''liaig''. The cognate form in [[Swedish]] is ''läkare'', and this still translates as [[physician]] (see [[List of false friends between Swedish and English]]).
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Leech saliva contains a number of compounds which assist in its feeding.  An [[anaesthetic]] limits the sensations felt by the host (and thus reduces the chance of the host trying to detach the leech).  A [[vasodilator]] causes the [[blood vessel]]s near the leech to become dilated, and thus provide the leech with a better supply.
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Lastly, the leech saliva contains a [[peptide]] called ''[[hirudin]]'', which is a highly effective anticoagulant.  The leech needs this to prevent [[blood clots]] (which would block its feeding) from forming in the wound created by its mouthparts. These properties are difficult to achieve using other medical techniques, and it is for this reason that leeches have come back into clinical practice in the last 25 years.
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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.
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==The anatomy of medicinal leeches==
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The anatomy of medicinal leeches may look simple, but more details are found beyond the macro level.  Externally, medicinal leeches tend to have a brown and red striped design on an olive colored background.  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.
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==Reproduction==
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Leeches are [[hermaphrodite]]s, meaning they are organisms that have both female and male  [[Sex organ|reproductive organs]] ([[ovary|ovaries]] and [[testicle|testes]] respectively). They also use [[clitellum]]s to hold the eggs.
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==Nutrition of leeches==
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[[Image:20070429EndauUpehGulingLeech.jpg|thumb|Typical leech found in Malaysian jungle.]]
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Starting from the anterior sucker is the jaw, the [[Pharynx]] which extends to the [[crop (anatomy)|crop]], which leads to the Intestinum, where it ends at the posterior sucker. The crop is a type of stomach that works like an expandable storage compartment. The crop allows a leech to store blood up to five times its body size; because of this ability to hold blood without the blood decaying, due to bacteria living inside the crop, medicinal leeches only need to feed two times a year.
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It was long thought that bacteria in the gut carried on [[digestion]] for the leech instead of endogenous enzymes which are very low or absent in the intestine. Relatively recently it has been discovered that all leeches and leech species studied do produce endogenous intestinal exopeptidases which can unlink free terminal-end [[amino acid]]s, one amino acid monomer at a time, from a gradually unwinding and degrading protein polymer. However, unzipping of the protein can start from either the amino (tail) or carboxyl (head) terminal-end of the [[Protein|protein molecule]]. It just so happens that the leech [[exopeptidase]] (arylamidases), possibly aided by proteases from endosymbiotic bacteria in the intestine, starts from the tail or amino protein, free-end, slowly but progressively removing many hundreds of individual terminal amino acids for resynthesis into proteins that constitute the leech. Since leeches lack [[endopeptidases]], the mechanism of protein digestion can not follow the same sequence as it would in all other animals where [[exopeptidases]] act sequentially on peptides produced by the action of [[endopeptidases]]. [[Exopeptidases]] are especially prominent in the common North American worm-leech Erpobdella punctata. This evolutionary choice of exopeptic digestion in Hirudinea distinguishes these carnivorous clitellates from Oligochaeta.
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Deficiency of [[digestive enzyme]]s (except exopeptidases) but more importantly deficiency of vitamins, B complex for example, in leeches is compensated for by enzymes and vitamins produced by endosymbiotic microflora. In ''Hrudo medicinalis'' these supplementary factors are produced by an obligatory [[Symbiosis|symbiotic relationship]] with a single bacterium species, ''Aeromonas hydrophila'', which maintains itself in [[pure culture]] by secreting an antibiotic known to medicine since the 19th century, well before Fleming's 1929 [[discovery of penicillin]]. Non-bloodsucking leeches such as ''E. punctata'' are host to three bacterial symbionts, ''[[Pseudomonas]]'' sp., ''[[Aeromonas]]'' sp., and ''[[Klebsiella]]'' sp. (a slime producer). The bacteria are passed from parent to offspring in the cocoon as it is formed.
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==Leech bites==
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===Effects===
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[[Image:Attached_Leech.jpg|thumb|A Borneo leech. Note how the leech curls and fattens as it fills with blood.]]
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A leech attaches itself when it bites, and it will stay attached until it has had its fill of blood. It has been known to suck all the blood out of its host. Due to an [[anticoagulant]] ([[hirudin]]) that leeches [[secrete]], bites may bleed more than a normal wound after the leech is removed.  The effect of the anticoagulant will wear off several hours after the leech is removed and the wound is cleaned.
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Leeches normally carry parasites in their [[Gastrointestinal tract|digestive tract]] which cannot survive in humans and do not pose a threat. However, bacteria, viruses, and parasites from previous blood sources can survive within a leech for months, and may be retransmitted to humans. A study found both [[HIV]] and [[hepatitis|hepatitis B]] in African leeches from [[Cameroon]].<ref name="nehili">Nehili, M., C. Ilk, H. Mehlhorn, K. Ruhnau, W. Dick, M. Njayou. [http://www.ncbi.nlm.nih.gov/sites/entrez?Db=PubMed&Cmd=ShowDetailView&TermToSearch=8073013 Experiments on the possible role of leeches as vectors of animal and human pathogens: a light and electron microscopy study]. ''(Abstract Only).'' ''Parasitology Research''. 1994;80(4):277-90, PubMed ID 8073013. Retrieved on [[2007]]-[[07-28]].</ref>
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===Removal===
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One recommended method of removal is using a fingernail to break the seal of the oral sucker at the anterior end (the smaller, thinner end) of the leech, repeating with the posterior end, then flicking the leech away. As the fingernail is pushed along the person's skin against the leech, the suction of sucker's seal is broken, at which point the leech should detach its jaws.<ref name=timesonline>[http://driving.timesonline.co.uk/tol/life_and_style/driving/article600016.ece The Knowledge: Removing a leech] Times Online. [[2006]]-[[10-15]]. Retrieved on [[2007]]-[[07-28]].</ref><ref name=worstcase>[http://www.worstcasescenarios.com/scenario.htm?scenarioid=22 Scenario Archive, Travel Survival: How to Remove a Leech] Worst Case Scenarios. Retrieved on [[2007]]-[[07-28]].</ref>
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A common but medically inadvisable technique to remove a leech is to apply a flame, lit cigarette, salt, or caustic chemical such as alcohol, vinegar, lemon juice, insect repellent, [[heat rub]], or certain carbonated drinks.  These cause the leech to regurgitate its stomach contents into the wound and quickly detach.  The vomit may carry disease and increases the risk of infection.<ref name="timesonline" /><ref name="worstcase" /><ref name=poisonscentre>[http://www.rch.org.au/poisons/stings.cfm?doc_id=3693 Victorian Poisons Information Centre: Leeches] Victorian Poisons Information Centre. Retrieved on [[2007]]-[[07-28]].</ref>
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Simply pulling a leech off by grasping it can also cause regurgitation, and adds risks of further tearing the wound, and leaving parts of the leech's jaw in the wound, which can also increase the risk of infection.
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An externally attached leech will detach and fall off on its own when it is satiated on blood, usually in about 20 minutes,<ref name="poisonscentre" /> while internal attachments, such as nasal passage or vaginal attachments, are likelier to require medical intervention.<ref>Ibrahim, Adibah, Hakim Bilal Gharib, and Mohd. Nizar Bidin. [http://www.ispub.com/ostia/index.php?xmlFilePath=journals/ijgo/vol2n2/leech.xml An Unusual Cause Of Vaginal Bleeding: A Case Report] The Internet Journal of Gynecology and Obstetrics. 2003. Vol. 2, No. 2, ISSN: 1528-8439. Retrieved on [[2007]]-[[07-28]].</ref><ref>[http://www.abc.net.au/news/stories/2005/04/11/1342694.htm Blood-sucker gets up woman's nose] Reuters via ABC News. [[2005]]-[[04-11]]. Retrieved on [[2007]]-[[07-28]].</ref>
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===Treatment===
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After removal or detachment, the wound should be cleaned with soap and water, and bandaged. Bleeding may continue for some time, due to the leech's anti-clotting enzyme. Applying pressure can reduce bleeding, although blood loss from a single bite is not dangerous. The wound normally itches as it heals, but should not be scratched as this may complicate healing and introduce other infections. An [[antihistamine]] can reduce itching, and applying a cold pack can reduce pain or swelling.
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Some people suffer severe allergic or [[anaphylaxis|anaphylactic reactions]] from leech bites, and require
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urgent medical care. Symptoms include red blotches or an itchy rash over the body, swelling away from the
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bitten area (especially around the lips or eyes), feeling faint or dizzy, and difficulty breathing.<ref name="poisonscentre" />
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===Prevention===
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There is no guaranteed method of preventing leech bites in leech-infested areas.  The most reliable method is to cover exposed skin.  The effect of [[insect repellent]]s is disputed, but it is generally accepted that strong (maximum strength or tropical) insect repellents do help prevent bites.
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Leech socks can be helpful in preventing bites when the full body will not be at risk of contact with leeches.  Leech socks are pulled over the wearer’s trousers to prevent leeches reaching the exposed skin of the legs and attaching there or climbing towards the torso.  The socks are generally a light color that also makes it easier to spot leeches climbing up from the feet and looking for skin to attach to.
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There are many [[Home remedy|home remedies]] to help prevent leech bites.  Many people have a great deal of faith in these methods, but none of them has been proven to have much or any effect.  Home remedies include: a dried residue of bath soap, tobacco leaves between the toes, pastes of salt or [[Sodium bicarbonate|baking soda]], citrus juice, and [[Eucalyptus|eucalyptus oil]].  Diluted [[Calcium hydroxide]] may also be used as a repellent, but may be damaging or irritating to the skin.
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==References==
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* Sawyer, Roy T. 1986. ''Leech Biology and Behaviour''. Vol 1-2. [[Oxford University Press|Clarendon Press]], Oxford
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<references />
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==See also==
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* [[Tempest Prognosticator]] &ndash; the application of leeches in a [[barometer]]
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==External links==
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{{Commons|Hirudinea}}
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{{Wikispecies|Hirudinea}}
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{{Wikibookspar|Dichotomous Key|Hirudinea}}
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* [http://www.amonline.net.au/factsheets/leeches.htm Leech fact sheet], [[Australian Museum]]
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* [http://www.glooskapandthefrog.org/leach.htm North American leeches]
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* [http://www.wildmadagascar.org/overview/leeches.html How to remove a leech]
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* [http://www.disgustingly-healthy.com Biotherapy with leeches and maggots]
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[[Category:Life sciences]]
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[[Category:Animals]]
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[[Category:Invertebrates]]
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{{credit|Leech|161997814}}

Revision as of 12:39, 3 October 2007


Leeches
A Leech on stones
A Leech on stones
Scientific classification
Kingdom: Animalia
Phylum: Annelida
Class: Clitellata
Subclass: Hirudinea
Lamarck, 1818
Genus: Macrobdella
Orders

Arhynchobdellida or Rhynchobdellida
There is some dispute as to whether Hirudinea should be a class itself, or a subclass of the Clitellata.

Leeches are annelids comprising the subclass Hirudinea. There are fresh water, terrestrial and marine leeches. Like their near relatives, the Oligochaeta, they share the presence of a clitellum. Like earthworms, leeches are hermaphrodites. The medicinal leech, Hirudo medicinalis, which is native to Europe, and its congeners have been used for clinical bloodletting for thousands of years.

All leech species are carnivorous. Some are predatory, feeding on a variety of invertebrates such as worms, snails, insect larvae, crustaceans, while a very few are haemophagic parasitic blood-sucking leeches, feeding on the blood of vertebrates such as amphibians, reptiles, waterfowl, fish, and mammals (including humans). The most important predators of leeches are fish, aquatic insects, crayfish and other leeches specialized for predation on leeches.

Haemophagic leeches attach to their hosts and remain there until they become full, at which point they fall off to digest. Leeches' bodies are composed of 34 segments. They all have an anterior (oral) sucker formed from the first six segments of their body, which is used to connect to a host for feeding, and can also release an anesthetic to prevent the host from noticing the leech. They use a combination of mucus and suction (caused by concentric muscles in those six segments) to stay attached and secrete an anti-clotting enzyme into the host's blood stream.

Some species of leech will nurture their young, providing food, transport, and protection, which is unusual behavior in an invertebrate.

Notes on annelids from NWE article on annelids

The annelids (from Latin anellus "little ring") are a large phylum (Annelida) of invertebrate animals, comprising the segmented worms, including the well-known earthworms and leeches. There are about 15,000 known modern species of annelids.

Annelids are found in most wet environments and include many terrestrial, freshwater, and especially marine species (such as the polychaetes), as well as some which are parasitic or mutualistic. They range in length from under a millimeter to over three meters (the seep tube worm Lamellibrachia luymesi).

In addition to enhancing the diversity of nature, which brings so much joy to humans, the segmented worms are ecologically and medically important. They are common in marine, freshwater, and terrestrial environments, serving as part of the food chain, and helping to turn over the soil and sediments. Some segmented worms have commercial use as bait for sport fishing or food for tropical aquarium fish. The leech can be used medically, for example, in controlling swelling, as it produces chemicals that can serve as an anesthetic and prevent blood coagulation.

Classes and subclasses of annelida

The three major groups of annelids are the polychaetes (largely marine annelids, with over 5,500 species); the oligochaetes (earthworms and freshwater worms, with over 3,000 species); and the hirundinea (leeches, with about 500 species). However, biological classification of annelids can vary widely among taxonomists.

Some consider there to be three classes of annelids: Polychaeta, Clitellata, and Aelosomata. The Clitellata are then further divided into three or four subclasses: Oligochaeta (earthworms and freshwater worms), Hirundinea (leeches), and Branchiobdella (about 150 species of small animals that are largely parasites or commensals on crayfish), and sometimes Acanthobdellida (leech-like, temporary parasite, which is also placed in Hirundinea in some classifications). Aelosomata includes small to very small annelides, with about 25 known species. This taxonomy looks like the following:

Class Polychaeta
Class Aelosomata
Class Clitellata
Oligochaeta - earthworms and so forth
Branchiobdellida — small, largely parasites or commensuals
Hirudinea - leeches
Acanthobdellida (sometimes part of Hirudinea)

Another taxonomic scheme regards two groups of polychaetes—the Archiannelida and the Myzostomaria—as classes in their own right, and recognizes four total classes: Polychaeta, Clitellata, Myzostomida, and Archiannelida. This looks like the following:

Class Polychaeta
Class Clitellata
Oligochaeta
Branchiobdellida
Hirudinea
Class Myzostomida
Class Archiannelida

In some biological classifications, the Clitellata is considered a subphylum and the Oligochaeta, Hirudinea and Branchiobdellida are treated as classes of this subphylusm.

A simple classification scheme is to recognize two classes of annelids, the Polychaeta and the Clitellata:

  • Clitellata
    • Oligochaeta - The class Oligochaeta includes the megadriles (earthworms), which are both aquatic and terrestrial, and the microdrile families such as tubificids, which include many marine members as well.
    • Leeches (Hirudinea) - These include both bloodsucking external parasites and predators of small invertebrates.
  • Polychaeta - This is the largest group of annelids and the majority are marine. All segments are identical, each with a pair of parapodia. The parapodia are used for swimming, burrowing, and the creation of a feeding current.

There have also been proposals to consider the Clitellata as part of the Polychaeta, thus making the latter term synonymous with the annelids.

Anatomy

Annelids are triploblastic protostomes with a coelom (at least historically), closed circulatory system, and true segmentation. Protosomes are animals with bilaterial symmetry where the first opening in development, the blastophore, becomes its mouth. Triploblastic means that they have three primary tissue areas formed during embryogenesis. A coelom is a fluid-filled body cavity.

Polychaeta: "A variety of marine worms" plate from Das Meer by M. J. Schleiden (1804–1881)

Oligochaetes and polychaetes typically have spacious coeloms; in leeches, the coelom is largely filled in with tissue and reduced to a system of narrow canals; archiannelids may lack the coelom entirely. The coelom is divided into a sequence of compartments by walls called septa. In the most general forms, each compartment corresponds to a single segment of the body, which also includes a portion of the nervous and (closed) circulatory systems, allowing it to function relatively independently. Each segment is marked externally by one or more rings, called annuli. Each segment also has an outer layer of circular muscle underneath a thin cuticle and epidermis, and a system of longitudinal muscles. In earthworms, the longitudinal muscles are strengthened by collagenous lamellae; the leeches have a double layer of muscles between the outer circulars and inner longitudinals. In most forms, they also carry a varying number of bristles, called setae, and among the polychaetes a pair of appendages, called parapodia.

Anterior to the true segments lies the prostomium and peristomium, which carries the mouth, and posterior to them lies the pygidium, where the anus is located. The digestive tract is quite variable but is usually specialized. For example, in some groups (notably most earthworms) it has a typhlosole (internal fold of the intestine or intestine inner wall), to increase surface area, along much of its length.

Different species of annelids have a wide variety of diets, including active and passive hunters, scavengers, filter feeders, direct deposit feeders that simply ingest the sediments, and blood-suckers.

The vascular system and the nervous system are separate from the digestive tract. The vascular system includes a dorsal vessel conveying the blood toward the front of the worm, and a ventral longitudinal vessel that conveys the blood in the opposite direction. The two systems are connected by a vascular sinus and by lateral vessels of various kinds, including in the true earthworms, capillaries on the body wall.

The nervous system has a solid, ventral nerve cord from which lateral nerves arise in each segment. Every segment has an autonomy; however, they unite to perform as a single body for functions such as locomotion. Growth in many groups occurs by replication of individual segmental units; in others, the number of segments is fixed in early development.


Phylogeny

The leeches are presumed to have evolved from the Oligochaeta, most of which feed on detritus. However, some species in the Lumbriculidae are predaceous and have similar adaptations to the leeches.

True leeches, of the subclass Euhirudinea, with both anterior and posterior suckers, are divided into two groups:

  1. Rhynchobdellae: "jawless" leeches, armed with a muscular straw-like proboscis puncturing organ in a retractable sheath. The Rhynchobdellae consist of two families: The Glossiphoniidae (flattened leeches with a poorly defined anterior sucker) and the Piscicolidae (have cylindrical bodies and a usually well-marked, bell-shaped, anterior sucker). The Glossiphoniidae live in fresh-water habitats; the Pisciolidae are found in sea-water habitats.
  2. Arhynchobdellids: Leeches which lack a proboscis and which may or may not have jaws armed with teeth. Arhynchobdellids are divided into two orders: Gnathobdellae and Pharyngobdellae
    1. Gnathobdellae: In this order of "jawed" leeches, armed with teeth, is found the quintessential leech: the European medical (bloodsucking) leech, Hirudo medicinalis. It has a tripartite jaw filled with hundreds of tiny sharp teeth. The incision mark left on the skin by the European medical leech is an inverted Y inside a circle. Its North American counterpart is Macrobdella decora, a much less efficient medical leech. Within this order, the family Hirudidae is characterized by aquatic leeches and the family Haemadipsidae by terrestrial leeches. In the latter are Haemadipsa sylvestris, the Indian leech and Haemadipsa zeylanica (Yamabiru), the Japanese Mountain or Land leech.[1]


    1. Pharyngobdellae: These so called worm-leeches consist of freshwater or amphibious leeches that have lost the ability to penetrate a host's tissue and suck blood. They are carnivorous and equipped with a relatively large, toothless, mouth to ingest worms or insect larvae, which are swallowed whole.

The Pharyngobdellae have six to eight pairs of eyes, as compared with five pairs in Gnathobdelliform leeches, and include three related families. The Erpobdellidae are some species from freshwater habitats.

Use of Hirudo medicinalis in medicine

The leech has long been used in medicine, previously being used to remove poison from the human body, although today its use is mainly limited in limb reattachment procedures instead of the wide-ranging medical use in the past. Leeches have proven highly effective at preventing venous congestion after the surgical re-attachment of fingers, toes, ears and other parts of the body. The word leech either comes directly from or was influenced by the Old English word for "physician", lǣce, which is related to Old High German lāhhi and Old Irish liaig. The cognate form in Swedish is läkare, and this still translates as physician (see List of false friends between Swedish and English).

Leech saliva contains a number of compounds which assist in its feeding. An anaesthetic limits the sensations felt by the host (and thus reduces the chance of the host trying to detach the leech). A vasodilator causes the blood vessels near the leech to become dilated, and thus provide the leech with a better supply.

Lastly, the leech saliva contains a peptide called hirudin, which is a highly effective anticoagulant. The leech needs this to prevent blood clots (which would block its feeding) from forming in the wound created by its mouthparts. These properties are difficult to achieve using other medical techniques, and it is for this reason that leeches have come back into clinical practice in the last 25 years.

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.

The anatomy of medicinal leeches

The anatomy of medicinal leeches may look simple, but more details are found beyond the macro level. Externally, medicinal leeches tend to have a brown and red striped design on an olive colored background. 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.

Reproduction

Leeches are hermaphrodites, meaning they are organisms that have both female and male reproductive organs (ovaries and testes respectively). They also use clitellums to hold the eggs.

Nutrition of leeches

Typical leech found in Malaysian jungle.

Starting from the anterior sucker is the jaw, the Pharynx which extends to the crop, which leads to the Intestinum, where it ends at the posterior sucker. The crop is a type of stomach that works like an expandable storage compartment. The crop allows a leech to store blood up to five times its body size; because of this ability to hold blood without the blood decaying, due to bacteria living inside the crop, medicinal leeches only need to feed two times a year.

It was long thought that bacteria in the gut carried on digestion for the leech instead of endogenous enzymes which are very low or absent in the intestine. Relatively recently it has been discovered that all leeches and leech species studied do produce endogenous intestinal exopeptidases which can unlink free terminal-end amino acids, one amino acid monomer at a time, from a gradually unwinding and degrading protein polymer. However, unzipping of the protein can start from either the amino (tail) or carboxyl (head) terminal-end of the protein molecule. It just so happens that the leech exopeptidase (arylamidases), possibly aided by proteases from endosymbiotic bacteria in the intestine, starts from the tail or amino protein, free-end, slowly but progressively removing many hundreds of individual terminal amino acids for resynthesis into proteins that constitute the leech. Since leeches lack endopeptidases, the mechanism of protein digestion can not follow the same sequence as it would in all other animals where exopeptidases act sequentially on peptides produced by the action of endopeptidases. Exopeptidases are especially prominent in the common North American worm-leech Erpobdella punctata. This evolutionary choice of exopeptic digestion in Hirudinea distinguishes these carnivorous clitellates from Oligochaeta.

Deficiency of digestive enzymes (except exopeptidases) but more importantly deficiency of vitamins, B complex for example, in leeches is compensated for by enzymes and vitamins produced by endosymbiotic microflora. In Hrudo medicinalis these supplementary factors are produced by an obligatory symbiotic relationship with a single bacterium species, Aeromonas hydrophila, which maintains itself in pure culture by secreting an antibiotic known to medicine since the 19th century, well before Fleming's 1929 discovery of penicillin. Non-bloodsucking leeches such as E. punctata are host to three bacterial symbionts, Pseudomonas sp., Aeromonas sp., and Klebsiella sp. (a slime producer). The bacteria are passed from parent to offspring in the cocoon as it is formed.

Leech bites

Effects

A Borneo leech. Note how the leech curls and fattens as it fills with blood.

A leech attaches itself when it bites, and it will stay attached until it has had its fill of blood. It has been known to suck all the blood out of its host. Due to an anticoagulant (hirudin) that leeches secrete, bites may bleed more than a normal wound after the leech is removed. The effect of the anticoagulant will wear off several hours after the leech is removed and the wound is cleaned.

Leeches normally carry parasites in their digestive tract which cannot survive in humans and do not pose a threat. However, bacteria, viruses, and parasites from previous blood sources can survive within a leech for months, and may be retransmitted to humans. A study found both HIV and hepatitis B in African leeches from Cameroon.[2]

Removal

One recommended method of removal is using a fingernail to break the seal of the oral sucker at the anterior end (the smaller, thinner end) of the leech, repeating with the posterior end, then flicking the leech away. As the fingernail is pushed along the person's skin against the leech, the suction of sucker's seal is broken, at which point the leech should detach its jaws.[3][4]

A common but medically inadvisable technique to remove a leech is to apply a flame, lit cigarette, salt, or caustic chemical such as alcohol, vinegar, lemon juice, insect repellent, heat rub, or certain carbonated drinks. These cause the leech to regurgitate its stomach contents into the wound and quickly detach. The vomit may carry disease and increases the risk of infection.[3][4][5]

Simply pulling a leech off by grasping it can also cause regurgitation, and adds risks of further tearing the wound, and leaving parts of the leech's jaw in the wound, which can also increase the risk of infection.

An externally attached leech will detach and fall off on its own when it is satiated on blood, usually in about 20 minutes,[5] while internal attachments, such as nasal passage or vaginal attachments, are likelier to require medical intervention.[6][7]

Treatment

After removal or detachment, the wound should be cleaned with soap and water, and bandaged. Bleeding may continue for some time, due to the leech's anti-clotting enzyme. Applying pressure can reduce bleeding, although blood loss from a single bite is not dangerous. The wound normally itches as it heals, but should not be scratched as this may complicate healing and introduce other infections. An antihistamine can reduce itching, and applying a cold pack can reduce pain or swelling.

Some people suffer severe allergic or anaphylactic reactions from leech bites, and require urgent medical care. Symptoms include red blotches or an itchy rash over the body, swelling away from the bitten area (especially around the lips or eyes), feeling faint or dizzy, and difficulty breathing.[5]

Prevention

There is no guaranteed method of preventing leech bites in leech-infested areas. The most reliable method is to cover exposed skin. The effect of insect repellents is disputed, but it is generally accepted that strong (maximum strength or tropical) insect repellents do help prevent bites.

Leech socks can be helpful in preventing bites when the full body will not be at risk of contact with leeches. Leech socks are pulled over the wearer’s trousers to prevent leeches reaching the exposed skin of the legs and attaching there or climbing towards the torso. The socks are generally a light color that also makes it easier to spot leeches climbing up from the feet and looking for skin to attach to.

There are many home remedies to help prevent leech bites. Many people have a great deal of faith in these methods, but none of them has been proven to have much or any effect. Home remedies include: a dried residue of bath soap, tobacco leaves between the toes, pastes of salt or baking soda, citrus juice, and eucalyptus oil. Diluted Calcium hydroxide may also be used as a repellent, but may be damaging or irritating to the skin.

References
ISBN links support NWE through referral fees

  • Sawyer, Roy T. 1986. Leech Biology and Behaviour. Vol 1-2. Clarendon Press, Oxford
  1. ↑ http://www.youtube.com/watch?v=ye4N2ZeJESA Video Japanese Mountain leech
  2. ↑ Nehili, M., C. Ilk, H. Mehlhorn, K. Ruhnau, W. Dick, M. Njayou. Experiments on the possible role of leeches as vectors of animal and human pathogens: a light and electron microscopy study. (Abstract Only). Parasitology Research. 1994;80(4):277-90, PubMed ID 8073013. Retrieved on 2007-07-28.
  3. ↑ 3.0 3.1 The Knowledge: Removing a leech Times Online. 2006-10-15. Retrieved on 2007-07-28.
  4. ↑ 4.0 4.1 Scenario Archive, Travel Survival: How to Remove a Leech Worst Case Scenarios. Retrieved on 2007-07-28.
  5. ↑ 5.0 5.1 5.2 Victorian Poisons Information Centre: Leeches Victorian Poisons Information Centre. Retrieved on 2007-07-28.
  6. ↑ Ibrahim, Adibah, Hakim Bilal Gharib, and Mohd. Nizar Bidin. An Unusual Cause Of Vaginal Bleeding: A Case Report The Internet Journal of Gynecology and Obstetrics. 2003. Vol. 2, No. 2, ISSN: 1528-8439. Retrieved on 2007-07-28.
  7. ↑ Blood-sucker gets up woman's nose Reuters via ABC News. 2005-04-11. Retrieved on 2007-07-28.

See also

  • Tempest Prognosticator – the application of leeches in a barometer

External links

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