Whether being rubbed away with salt by Humphrey Bogart in the "African Queen" or the ghastly aftermath of an impromptu boyhood swim as portrayed in "Stand By Me," the thought of the common pond leech fastening its circular mouth is a repugnant one.

Leeches are indigenous to most of the world, excluding deserts and artic regions, with over 650 distinct species. Each leech has both female and male reproductive organs but cannot self-propagate. Though not all leech species feed on blood, those that do have adapted in impressive ways to insure a successful meal.

They have two mouths, one for feeding and one for secure attachment to its host. Their saliva contains several compounds that include an anesthetic, an anticoagulant, a vasodilator, and hyaluronidase. The anesthetic allows the nematode to attach without the host noticing. The anticoagulant, called hirudin, prevents the body's normal clotting mechanism from interrupting the leech's meal. Histamine, a powerful vasodilator, increases blood flow to the attachment site. The enzyme, hyaluronidase, tenderizes flesh in the immediate area, which permits the parasite a firmer hold. The leech has perfected the complexities of subtle trespass.

Indeed, the finesse with which the leech performs its natural function has impressed mankind since the beginning of medical record keeping. The Egyptians used leeches as early as 1500 BC, with older mentions in Arabic, Sanskrit, and Persian literature. The use of leeches continued unabated through the Middle Ages and the Renaissance. Graphic medieval texts illustrate proper placement and describe the diseases to be treated.

Knowledge of early medical theory explains the fascination. Ancient philosophers imagined a healthy body as a holistically balanced entity. Disease resulted if one of the four humors - blood, phlegm, black bile, and yellow bile - were disrupted. If the imbalance was determined to be in the blood, then releasing that humor followed. Sometimes this was accomplished by inserting a blade into a palpable vein, a chancy prospect, but considering how effectively they accomplished the task leeches became the method of choice.

By using leeches, each of which would take a predictable amount, the therapy became standardized. Physicians prescribed the volume of blood that should be removed and practitioners, who became known as leeches, applied the correct number of parasites that would achieve the desired goal.

The application of leeches remained a popular cure for a plethora of maladies, including fevers, obesity, and edema, until the mid 1800's. Eventually, the practice fell out of favor as medical knowledge expanded, other treatments found acceptance, and pharmacology improved but not before Hirudo medicinalis, the most popular species of medical leech, had become scarce in its natural environment and expensive to procure.

Leeches were used as recently as 1930 for the management of Congestive Heart Failure.

Far from becoming a mere historical curiosity, the leech continues to be an actively studied therapeutic tool and not only for the medicinal value of the numerous intriguing salivary secretions.

Microsurgery, including the reattachment of fingers, toes, ears, and scalp, has discovered an important use for the bloodletting function of the lowly, repulsive leech. Though arterial blood flow into a severed digit can be reestablished with reasonable certainty, the flow out is not as easily regained. The thousands of capillaries and lesser vessels of the venous system are impossible to reconnect at present. The blood comes in but cannot get out, which leads to engorgement, congestion, coagulation, and eventual gangrene. In time, the body can regenerate a return flow into even the most traumatized tissue but how can surgeons buy that time without losing the transplanted or reattached parts?

Leeches. By their very nature, these little monstrosities are white knight saviors for survivors of accidental amputation. Their profound complex secretions provide anti-clotting factors and their limited appetite removes accumulated venous congestion. The anticoagulant function lasts longer than the period of time in which the parasite feeds, which prevents further damage from clotting in the nascent capillary regrowth. The histamine encourages circulation.

Though no surgeon advertises the fact, most keep a supply in a handy laboratory refrigerator. The nematodes hibernate at cool temperatures and, when warmed, wake up very hungry and enthusiastically participate in their newest medical function. Modern leeches are raised on farms, cost about ten dollars each, and are disposed of as biohazardous material once they finish their single meal.

In immuno-compromised patients, leech therapy occasionally causes an infection of Aeromonas hydrophila, a symbiotic bacteria that inhabits leech intestines.

Mechanical devices have, so far, not proven to be superior in efficacy to Hirudo medicinalis, but research for leech replacement continues for two reasons.

Modern sensibilities are offended by reliance on low-tech solutions.

But the primary reason for seeking out alternatives is that people don't like the idea of being beholden to the slimy, maligned, and misrepresented leech - or the possibility of being its lunch.

References

Leeches in Modern Medicine Sound Medicine.com

A Leech for the New Millennium BBC News

Medical Use of Medicinal Leeches by J.Graf

Minkin, Bruce I, MD Leeches Reprinted from Carolina Tips, February 1, 1990, Vol. 52, No.2

Medicinal Leeches University of Missouri Health Care

"Leeches - Hirundinea Action of Biology in Education

Medical Uses of Leeches The Leech Lady

Lisa Binkley works within the medical industry and is the popular author of this health series in the Kudzu Monthly. She also serves as the fiction editor of this ezine, edits for the online sci-fi magazine Distant Worlds, and maintains her own site for her fanciful sci-if work called Jolie Howard Fiction.

As Lisa phrases it, "Woman, wife, worker, writer. We all wear many faces and fill our niches as best we can."

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