Leeches are bloodsucking worms with segmented bodies. They belong to the samelarge classification of worms as earthworms and certain oceanic worms.

Leeches can primarily be found in freshwater lakes, ponds, or rivers. They range in size from 0.2 in (5 mm) to nearly 18 in (45 cm) and have two characteristic suckers located at either end of their bodies. Leeches consume the blood of a wide variety of animal hosts, ranging from fish to humans. To feed, aleech first attaches itself to the host using the suckers. One of these suckers surrounds the leech's mouth, which contains three sets of jaws that bite into the host's flesh, making a Y-shaped incision. As the leech begins to feed, its saliva releases chemicals that dilate blood vessels, thin the blood, and deaden the pain of the bite. Because of the saliva's effects, a person bitten by a leech may not even be aware of it until afterwards, when he or she sees the incision and the trickle of blood that is difficult to stop.

For centuries, leeches were a common tool of doctors, who believed that manydiseases were the result of "imbalances" in the body that could be stabilizedby releasing blood. For example, leeches were sometimes attached to veins inthe temples to treat headaches. Advances in medical knowledge led doctors toabandon bloodletting and the use of leeches in the mid-nineteenth century. In recent years, however, doctors have found a new purpose for leeches--helping to restore blood circulation to grafted or severely injured tissue.

There are many occasions in medicine, mostly in surgery and trauma care, whenblood accumulates and causes trouble. Leeches can be used to reduce the swelling of any tissue that is holding too much blood. This problem is most likely to occur in two situations:

  • Trauma. Large blood clots resulting from trauma can threaten tissue survival by their size and pressure. Blood clotscan also obstruct the patient's airway.
  • Surgical procedures involving reattachment of severed body parts or tissue reconstruction following burns. In these situations it is difficult for the surgeon to make a route for blood to leave the affected part and return to the circulation. The hardest part of reattaching severed extremities like fingers, toes and ears is to reconnect the tiny veins. If the veins are not reconnected, blood will accumulate in the injured area. A similar situation occurs when plastic surgeons move large flaps of skin to replace skin lost to burns, trauma or radical surgery. The skin flaps often drain blood poorly, get congested, and begin to die. Leeches have come to the rescue in both situations.

It is important to use only leeches that have been raised in the laboratory under sterile conditions in order to protect patients from infection. Therapeutic leeches belong to one of two species--Hirudo michaelseni or Hirudo medicinalis.

One or more leeches are applied to the swollen area, depending on the size ofthe graft or injury, and left on for several hours. The benefits of the treatment lie not in the amount of blood that the leeches ingest, but in the anti-bloodclotting (anticoagulant) enzymes in the saliva that allow blood to flowfrom the bite for up to six hours after the animal is detached, effectivelydraining away blood that could otherwise accumulate and cause tissue death. Leech saliva has been described as a better anticoagulant than many currentlyavailable to treat strokes and heart attacks. Active investigation of the chemicals in leech saliva is currently under way, and one anticoagulant drug, hirudin, is derived from the tissues of Hirudo medicinalis.

The leeches are removed by pulling them off or by loosening their grip with cocaine, heat, or acid. The used leeches are then killed by being placed in analcohol solution and disposed of as a biohazard. Proper care of the patient's sore is important, as is monitoring the rate at which it bleeds after the leech is removed. Any clots that form at the wound site during treatment should be removed to ensure effective blood flow.

Infection is a constant possibility until the sore heals. It is also necessary to monitor the amount of blood that the leeches have removed from the patient, since a drop in red blood cell counts could occur in rare cases of prolonged bleeding.

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