An overview of veterinary medicinal leeching

In the 18th and 19th centuries, medicinal leeching was popular for treating a variety of human illnesses, including mental disorders, whooping cough, gout, tumors, headaches and obesity. A lack of documented success led to a sharp decline in the use of leeches in the 20th century-that is, until its application in managing a common postoperative complication of microvascular surgery became evident.

Biology

More than 700 species of leeches are known to exist, but Hirudo medicinalis is the leech most commonly used in the medical field. It is a segmented invertebrate that can reach up to 20 cm as an adult and is usually brownish green with a dorsal red stripe (Figure 1). Leeches have a large sucker on their caudal end, which is used for crawling and attachment. The cephalad sucker is smaller and tapered and used for feeding. The mouths of these leeches consist of a tripartite jaw, which creates the typical star or Y-shaped bite, with 60 to 100 teeth total, and each mouth has its own secretory opening.

Figure 1. Hirudo medicinalis, the leech most commonly used in medicinal leeching, is a segmented invertebrate that can reach 20 cm in length and is usually brownish green with a dorsal red stripe. Photos courtesy of Dr. Nicole J. Buote.Sanguivorous leeches can store blood inside their bodies for months, and symbiotic bacteria-Aeromonas species located in the gut-secrete enzymes that help break down the components of blood. There are at least 100 bioactive compounds in leech saliva.1 The most commonly found is hirudin, which is responsible for inhibiting thrombin and thus gives the saliva its anticoagulant power. The leeching process is minimally invasive and pain-free because of an anesthetic, histamine-like substance that is found in leech saliva.

Each leech can remove about 5 to 10 ml of blood per feeding, and each site will continue to ooze blood for an additional 24 to 48 hours after detachment, allowing for an additional blood meal (5 to 10 ml) to be lost. An experimental study in pigs found that 90 percent of passive bleeding after detachment occurs within five hours.2

Clinical uses in human medicine

Medicinal leeching can be used to reduce complications of microvascular (e.g., replantation) or reconstructive surgeries (e.g., skin flaps), to decrease postoperative swelling from damaged venous structures, and to drain hematomas. Nontraditional uses of medicinal leeching include helping in the treatment of osteoarthritis, otitis media and compartment syndrome. The efficacy of leeches in salvaging flaps in human surgical patients has been widely proved, with some studies quantifiably illustrating increased blood flow throughout the leech-treated flap.3 The mechanism behind this process is thought to be a combination of relieving obstruction and capillary pressure and of increasing microcirculation because of vasoactive compounds injected by the leech.

Figure 2. Venous congestion leads to classic physical signs such as a bluish color, edema, brisk capillary return and warmth in the tissue.The most common complication with microvascular surgeries is venous congestion or thrombosis after microvascular anastomosis. Venous congestion can occur any time there is an imbalance between arterial inflow and venous outflow, which results in stasis of the blood in the affected area. Decreases in venous outflow can occur with constrictive wounds because of damage to venous structures during interventional radiography procedures or during reconstruction or replantation procedures because of the thin walls of the low capacitance veins, which are easily collapsed or torn. That results in decreased tissue perfusion, which can cause local hypoxia, acidosis, arterial thrombus formation and tissue necrosis. Venous congestion leads to classic physical signs such as a bluish color, edema, brisk capillary return and warmth in the tissue (Figures 2 and 3). Venous congestion is so common in the surgical replantation of auricles that it is considered by some to be an accompanying symptom rather than a complication.

Figure 3. Another photo of venous congestion.Medicinal leech therapy helps remove venous blood, which reduces the capillary filling pressure, so that damaged veins have time to recover and arterial capillary beds can reperfuse. Leech therapy is especially helpful with auricular replantation because of the challenging aspect of finding and reconnecting vessels of this size and the risk of damage to vessels during attempts at anastomosis. This difficulty is mirrored in many veterinary reconstructive techniques, as microvascular surgical techniques can be extremely difficult if not impossible in small animals.

Clinical uses in veterinary medicine

In veterinary medicine, there is one case report describing the use of leeches in treating polycythemia vera in a cat. Another case report describes using leeches in the treatment of a constrictive wound in a cat.4,5 The more recent case report also includes a detailed description of the biology of leeches, their clinical uses and application recommendations in small animals.

To see how medicinal leeching helped one cat, see Leech application to treat toe swelling in a cat. For a guide to leeching, see Veterinary medicinal leech therapy: Application, monitoring, complications. And to see leeches in action, see Videos of medicinal leechs in action.

Conclusion

Medicinal leech therapy should be considered an exciting new tool in your medical toolbox for use with challenging wound management and reconstructive surgeries. No complications were seen with this therapy in our patient, but specific recommendations regarding the handling of leeches, monitoring during leeching and patient management after leeching should be followed. Specifically, prophylactic antibiotics must be instituted, and depending on the number and length of leeching treatments, blood transfusions should be expected.

References

1. Green PA, Shafritz AB. Medicinal leech use in microsurgery. J Hand Surg Am 2010;35(6):1019-1021.

2. Conforti MI, Connor NP, Heisey DM, et al. Evaluation of performance characteristics of medicinal leech (Hirudo medicinalis) for the treatment of venous congestion. Plast Reconstr Surg 2002;109(1):228-235.

3. Whitaker IS, Oboumarzouk O, Rozen WM, et al. The efficacy of medicinal leeches in plastic and reconstructive surgery: a systematic review of 227 reported clinical cases. Microsurgery 2012;32(3):240-250.

4. Nett CS, Arnold P, Glaus TM. Leeching as initial treatment of a cat with polycythaemia vera. J Small Anim Pract 2001;42(11):554-556.

5. Buote NJ. The use of medical leeches for venous congestion. A review and case report. Vet Comp Orthop Traumatol 2014:27(3):173-178.

Dr. Buote was awarded Diplomate status in the American College of Veterinary Surgeons in 2010 after completing a residency at the Animal Medical Center in New York City. She is a published author on the subject of laparoscopy and heads the Minimally Invasive department at VCA California Animal Hospital Veterinary Specialty Group in Los Angeles, Calif.