leech

A specialized ringed worm related to the earthworms; body highly contractile, usually with a sucker at each end; many are blood-feeders on vertebrate hosts, others are predators of invertebrates; found in aquatic and damp terrestrial habitats. One species was used in early medicine for bleeding patients suffering from various illnesses. (Phylum: Annelida. Subclass: Hirudinea.)

?Leeches

A Leech on stones

Scientific classification

Kingdom:	Animalia
Phylum:	Annelida
Class:	Clitellata
Subclass:	Hirudinea Lamarck, 1818

Orders

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

All leech species are carnivorous. The most important predators on leeches are fishes, aquatic insects, crayfishes 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.

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

Origin

The leeches are presumed to have evolved from the Oligochaeta, most of which feed on detritus.

Taxonomy

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

Rhynchobdellae: "jawless" leeches, armed with a muscular straw-like proboscis puncturing organ in a retractable sheath. The Rhychobdellae 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). Arhychobdellids are divided into two orders: Gnathobdellae and Pharyngobdellae Gnathobdellae: In this order of "jawed" leeches, armed with teeth, is found the quintessential leech: the European medical (bloodsucking) leech, Hirudo medicinalis. Within this order, the family Hirudidae is characterized by aquatic leeches and the family Haemadipsidae by terrestrial leeches.

The Pharyngobdellae have six to eight pairs of eyes, as compared with five pairs in gnathobdelliform leeches, and include three related families.

Use of Hirudo medicinalis in medicine

The leech has long been used in medicine, although today its use is mainly limited to limb reattachment procedures instead of the wide-ranging medical use of the past.

Leech saliva contains a number of compounds which assist in its feeding. 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.

Bdellatomy is the practice of cutting the leech open slightly while it is sucking blood to let the blood in it out, so, thinking that it is not full yet, the leech continues to bite instead of detaching itself.

The anatomy of medicinal leeches

The anatomy of medicinal leeches may look simple, but more details are found beyond the macro level.

Reproduction

Leeches are hermaphrodites, meaning they are organisms that have both female, ovary, and male, testes, sexual reproductive organs.

Nutrition of leeches

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. 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. 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.

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.

The effects of leech bites

A Leech attaches itself when it bites, and it will stay attached until it has had its fill of blood. Due to an anticoagulant (hirudin) that leeches secrete, bites may bleed more than a normal wound after the leech is removed.

Leech bites tend to itch while healing, but this is normal.

Leeches do carry parasites in their digestive tract, but these cannot survive in humans and do not pose a threat.

Removal and Treatment

Many people believe that it is best not to remove a leech but to wait for the leech to have its fill and detach itself. This does prevent the risk of additional damage or complications from removal, but concerns about leaving portions of the leeches sucker attached to the wound are exaggerated.

Leeches should not be removed by burning or applying harsh agents such as salt. Most importantly, damaging the leech may cause it to regurgitate stomach bacteria that may lead to infection of the wound.

--Basic Instructions for Proper Removal and Treatment--

Do not attempt to crush or burn the leech. This is the sucker at the small end of the leech. Once the oral sucker is detached, quickly detach the sucker at the other end of the leech (the large end of the leech). This can be done by flicking the leech or by pushing the underside the leech and up against the sucker. Clean the wound to prevent infection, to remove detached sucker parts, and to remove the anticoagulant that the leech has secreted.

In the game Metal Gear Solid 3: Snake Eater, the protagonist, can also burn the leech with a lit cigar or cigarette to make it cringe and fall off, although this technique is not recommended, since it irritates the leech and causes it to regurgitate.

Prevention

There is no guaranteed method of preventing leech bites in leech-infested areas.

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.

There are many home remedies to help prevent leech bites.