Medical leeches are seen against a blood-streaked wall.

Leeches are still used in medicine—yes, really. Here’s why.

Long dismissed as a throwback to the Middle Ages, doctors have been turning to the parasites to help transplant and plastic surgery patients.

Medical leeches at a medicinal leech breeding facility in Biebertal, Germany.
Photograph by Tim Wegner, laif/Redux

A rare type of cancer called synovial sarcoma landed Ellie Lofgreen at the University of Utah Hospital this summer. Surgeons removed a tumor—the size of a small cantaloupe—wrapped around her knee joint and also cut out a few inches of bone and muscle connected to the knee. They inserted a metal implant in her leg and covered it with a large flap of muscle and skin transplanted from her upper thigh. But a few hours later, the flap began turning purple, a sign, the doctors knew, that the transplanted tissue was dying.

Saving the graft was critical so the medical team proposed a treatment that surprised Lofgreen: leeches.

“I was absolutely floored,” says the 31-year-old Idaho resident. “My initial reaction was, Okay, anything but that.”

Aside from the yuck factor, the use of leeches in modern medicine often surprises patients given that these blood-sucking parasites were long dismissed as quackery. But their use in plastic and reconstructive surgery has picked up since 2004, when the U.S. Food and Drug Administration approved leeches as a medical device to relieve congested veins and restore blood flow in compromised grafts.

When doctors attach a piece of tissue to another part of the body, they connect blood vessels in the graft to those in the surrounding tissue to maintain blood supply. Such surgeries are often successful, but in situations where they don’t go as planned, the first step is to take the patient back to the operating room, reexamine the stiches, and reattach the blood vessels. But, although rare, that fix can also fail.

“Veins are so fragile,” says Jayant Agarwal, chief of plastic surgery at the University of Utah. Despite making the connection, for example, blood flow could still be restrained because a vein end was damaged during an accident. Other times, finding a vein in a severed finger, for instance, may itself be a challenge. Without that connection, blood can pool in the transplanted tissue, and that’s when leeches come into play.

They provide temporary life support, says Jeffrey Janis, a plastic surgery expert at the Ohio State University Wexner Medical Center, until the body’s own blood vessels grow into this transferred piece of tissue. Without that help, the tissue can die, he says.

Where medical leeches come from

Although there are more than 600 species of leeches, including some that don’t suck blood, the European Hirudo medicinalis and Mediterranean Hirudo verbana are most frequently used in medicine. They have three saw-like jaws, each bearing about 100 teeth that the animals use to puncture skin.

For decades, laboratories in several countries including United Kingdom, United States, France, Turkey, and Ukraine have been breeding these medical leeches. Carl Peters-Bond at Biopharm U.K., a company that supplies about half of the medical leeches used in hospitals globally, has been doing this for nearly 30 years. It takes anywhere between a year and two years to raise a leech ready for medical use, he says. The process involves feeding them at three weeks, eight to 10 weeks, and then at four to five months, after which they’re starved for up to two years. “We only ship leeches with an empty gut,” he says.

As soon as an emergency call arrives, Peters-Bond packs between a dozen and 60 leeches in a gel-filled jar and ships them to a hospital. Sometimes, hospital pharmacies pre-order and stock medical leeches in a refrigerator for when a patient, with a severed finger, or in need of an ear reattachment or breast reconstruction surgery, may need them. But these creatures come with a best before three months date, Peters-Bond mentions.

How leech therapy works 

When a leech bites, it slowly sucks blood and injects compounds like hirudin and calin—present in its saliva—that keep the blood from clotting. Leech saliva also contains histamine-like substances that dilate blood vessels and improve blood flow. Physicians have also used anticoagulants like heparin to prevent blood clots from forming during reconstructive surgeries. But you still need the active sucking of blood, Agarwal says.

Depending on the size of the graft and the degree of congestion, leeching can continue for three to 10 days or more, until the tissue looks “less swollen, less purple, more normal,” Janis says. Patients remain in the hospital while medical staff supervise the process—replacing every engorged leech with a new starved one. Each critter can only be used once and is drowned in alcohol after it has served its purpose.

Over the course of two weeks, Lofgreen had more than 100 leeches drain her dingy-looking tissue. With help from nurses and crowdsourced suggestions via Facebook, her family named each one of these invertebrates. Some of Lofgreen’s favorites included Aleecha Keys, Clint Leechwood, Sir Leech-a-lot, and Queen Laleecha. Every four hours, a nurse would come in and place a new leech, which would suck blood anywhere between 15 to 120 minutes before falling off and landing on her bed. While undergoing the therapy, doctors gave her blood transfusions to replace the lost blood.

But getting the leech to latch on was a struggle sometimes; ensuring it stays where it should was trickier. Initially, nurses used a four-ounce plastic cup, which they inverted and taped onto Lofgreen’s skin to contain the leech. But the critter would often sneak out. The staff then created a barrier using a piece of gauze with a hole where they wanted the leech to attach; they hoped the gauze would discourage it from wandering off to surrounding skin. But that wasn’t foolproof either. What worked best was her mother’s and sister’s watchful eyes. Throughout the day they would take turns watching for rogue leeches and immediately alert the nurses. Lofgreen felt no sensation when these parasites bit into the transplanted tissue, but it pinched sharply when they bit elsewhere. “It was like pins and needles,” she says.

Over time, the part of her tissue that initially appeared dark and necrotic turned light purple and the skin looked more normal. “We had some success with the leeches,” Lofgreen says. But after she returned home, a small section of the flap got infected and had to be removed. The infection wasn’t linked to leeching but rather the result of an open wound. However, she credits the slimy slithering creatures with saving the majority of the transplanted flap.

A study that looked at 277 cases of medical leech use reported a 78 percent success rate. “It’s a very attractive option for flap salvage,” says Ernest Azzopardi, a plastic surgery specialist at University College London in England and co-author of the study. But a lack of robust randomized control trials, the gold standard for evaluating the effectiveness of an intervention, has meant less confidence in using leech therapy.

Another downside is that patients can develop skin infections in response to such treatments due to the Aeromonas bacteria that live in leech guts and are found in their saliva. Leech breeders like Peters-Bond don’t use antibiotics. Although the drugs could clear these gut bacteria, they come back, he says. “What we do is starve the leeches so there’s no presence of blood in the gut and the bacteria is at its minimum.” In hospitals, doctors typically prescribe patients antibiotics as a preventative measure, but evidence of some Aeromonas bacteria developing resistance to commonly-used drugs is emerging, making the therapy a challenging one to use.

Robotic leeches 

For years, scientists have been searching for alternatives to leeching. Early attempts date back to the 19th century when leeches were in high demand in Europe and the invertebrates were becoming scarce and thus more expensive. In 1817, Jean-Baptiste Sarlandière, a French anatomist and physiologist, for instance, developed a device called the bdellometer, which drained blood from patients.

Agarwal, for instance, has been working with colleagues at the University of Utah since 2013 to develop a mechanical leech that can deliver an anticoagulant but also mimic the leeches’ suction. The prototype consists of an array of needles that puncture the skin, where a central needle would supply the anti-coagulate heparin to the blood saturated tissue and surrounding needles connected to a pump would suction blood. This thumb pad-sized device would allow doctors to control the volume and rate of blood aspirated, which isn’t possible when using real leeches. For now, the team is trying to perfect the flow of anticoagulant into the tissue where the device is attached.

Other scientists, too, have developed similar prototypes that hold promise. Some have tested their performance in animals. But in terms of a mechanical replacement that’s ready for use in humans, “we’re not quite there yet,” Azzopardi says. For now, these blood-sucking parasites continue to hold a niche but important place in modern medicine.

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