Medicinal Leeches: Saliva In, Blood out

The saliva of medicinal leeches holds prized secrets

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Despite what some may say, the FDA never "approved" leeches as medical treatment.  Instead, in 2004, the feds told a French firm that they didn't need FDA approval to sell medicinal leeches as a medical device in the United States.  According to the FDA, leeches are similar to devices (presumably leeches) sold before May 28, 1976--the date the Medical Device Amendments was enacted.  Thus, no federal approval for leeches is needed.

You may argue that the point I make is semantic "approval" or "no approval" leeches are being sold and used for medical treatment in the United States.  Sure, the FDA isn't going to do anything to stop companies from selling leeches; however, the FDA is making no judgment as to their safety or efficacy--an integral distinction.  Furthermore, the feds have no obligation to rigorously review leeches as medical treatment and really understand the science of leech therapy.

Although leeches have been used as blood-letting therapy ever since antiquity, we still know little about these spineless, slimy creatures.  For the most part, research is limited to a small number of case studies and case series with no to very few randomized-control trials.  Nevertheless, what we do know about leeches hints at therapeutic greatness:  Leech saliva is a treasure trove of vasodilatory and anticoagulant (blood-thinning) molecules.

 

Medicinal leeches and their super spit

Leeches are blood-sucking (sanguivorous) worms.  Like earthworms, their bodies are segmented, and these little guys can extend, contract and contort in countless ways. (Shawn Johnson ain't got nothing on the leech!)  Hiruda medicinalis is the species of leech mostly used as medical therapy.

However, other types of leeches are used, too, including Hirudinaria granulosa in India and the American medicinal leech, Macrobdella decora.

A leech is an external parasite able to suck a quantity of blood several times its body weight from its host.  After it's mixed with glandular secretions which keep the blood from coagulating, leeches store this blood in lateral diverticula.  Thus, the blood from one feeding can serve as a nutritional reserve for several months.

Blood-letting or Hirudo therapy was first documented in ancient Egypt and continued in the West until the late 1800s, when the practice fell out of favor.  Curiously, despite falling out of favor in the West, the practice of leech phlebotomy persisted unabated in Inani or Islamic medicine. 

For decades, the leech has been used as a tool to help with microsurgery and plastic and reconstructive surgeries.  Moreover, scientists have just begun to appreciate the molecules that make up leech saliva and their potential applications.

Here are just some of the many wonderful molecular moieties found in leech spit:

  • Hirudin.  In 1950, a German scientist named Fritz Marquardt isolated a molecule that he named hirudin from the glandular secretion of Hiruda medicinalis.  It turns out that hirudin has many of the same anticoagulant properties as the blood thinner heparin without the nasty adverse effects.  Specifically, hirudin binds to thrombin with high affinity and doesn't cross react with antibodies in the patient with heparin-induced thrombocytopenia.  Moreover, hirudin can be used in people sensitized to heparin or in those who exhibit antithrombin III deficiency.  To date, researchers have developed various recombinant systems using bacteria, yeasts, and eukaryotes with the hope of harvesting enough hirudin for medical use.  The potential uses for hirudin are vast and include any disease with thrombotic (clot-forming) underpinnings like stroke, heart attack and deep venous thrombosis.
  • Hyaluronidase.  The enzyme hyaluronidase is sort of a tenderizer which loosens up (makes more permeable) human connective tissue thus helping the leech suck up blood.  It also helps facilitate analgesia and pain relief.  This enzyme is currently being examined for use in chemotherapy and the development of medications absorbed through the skin.
  • Calin.  Calin is a molecule that keeps platelets and von Willebrand factor, important mediators of clotting, from binding to collagen.  Collagen strengthens and elasticizes our skin. Thus, calin keeps blood flowing by inhibiting clotting.
  • Destabilase.  The enzyme destabilize has both thrombotic or clot-dissolving and antibacterial capabilities.  Research suggests that it may proffer applications akin to streptokinase or tissue plasminogen activator which are used in case of acute heart attack or stroke respectively.
  • Eglin.  This small protein is a thrombin inhibitor. It may someday contribute to the treatment the inflammation of shock and emphysema.

Modern uses of medicinal leeches

Especially in Europe, the use of leeches as medical therapy is becoming increasingly popular.  Currently, leeches and their anticoagulant powers are used for 3 main purposes. (Of note, even Aetna even covers such biosurgery.)

  • Leeches are used to salvage pedicled skin flaps which are used in plastic, maxillofacial and other reconstructive surgeries.  Each individual leech is used to drain an engorged flap of 5 to 10 mL of blood.  Such treatment is continued until the patient's own tissue bed can adequately drain venous blood.
  • Leeches help with microvascular tissue transfers where tissue from one part of your body is transferred to another part of your body.
  • Leeches help save replanted body parts from amputation by relieving vascular or venous engorgement.  Such body parts include fingers, the tip of the nose, nipples, ears, lips, and even the penis (which no doubt makes for a startling image).

Of note, leeches and their anti-inflammatory and analgesic properties are also being examined as a treatment for painful conditions like osteoarthritis.

As documented in a 2012 paper published in Wiley Periodicals, researchers compiled data from 277 case studies and series dating from 1966 to 2009 and procured from PubMed and other databases.  Of 229 patients, 50 or 21.8 percent experienced complications.  Nearly two-thirds of these complications were infectious.  Certain people who received leech therapy also required blood transfusions.

Based on the results of their research, authors of the Wiley study suggested that all patients who receive leech therapy be typed and screened for possible blood transfusion.  Additionally, such patients should be started on prophylactic antibiotics like quinolones.  Other sources suggest that a third-generation cephalosporin like ciprofloxacin may be best effective against bacteria distinct to the leech. 

Without a doubt, having leeches applied to your body registers pretty high on the "icky" scale.  Remember that it's your choice to allow a health care professional to apply leeches especially since alternative means of treatment exist.  However, although more rigorous research--prospective (long-term) and randomized control trials--need to be done,  what we do know about leeches is highly encouraging.  Moreover, molecular isolated from leech saliva may hold the key to better anticoagulant, antithrombotic, anti-inflammatory, and analgesic therapy.

Special shout-out to the wonderful Ms. Gina Wadas, a young science journalist and student in the science and technology journalism graduate program at Texas A&M University, for suggesting this topic.  Thanks, Gina!

Selected Sources

Divi V et al.  Chapter 78,  Microvascular Reconstruction.  In:  Lalwani AK. eds. Current Diagnosis and Treatment in Otolaryngology--Head & Neck Surgery, 3e.  New York, New York: McGraw-Hill; 2012.  Accessed 12/29/2014.

An article titled "The Efficacy of Medicinal Leeches in Plastic and Reconstructive Surgery: A Systematic Review of 277 Reported Clinical Cases" by IS Whitaker et al published in Wiley Periodicals, Inc. in 2012.  Accessed from PubMed on 12/28/2014.

An article titled "A Systematic Overview of the Medicinal Importance of Sanguivorous Leeches" by SM Abbas Zaidi et al published in Alternative Medicine Review in 2011.

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