The return of the leech

Jamie Levine, the chief of plastic surgery at Bellevue Hospital in New York City, is a hit at dinner parties; he always has a good story from the office. “Basically, we put back [body parts] that are cut off” – fingers, toes, noses, ears and even testicles, he says. So Levine knew exactly which tools to use when a young female bartender came in with a “ring degloving” — she got her ring caught on a hook, which pulled off a large area of skin on her finger, like taking off a glove.

Levine didn’t reach for a scalpel or forceps; instead, he used leeches. Using a needle, he pricked the end of the bartender’s injured finger to get the blood flowing. He then carefully placed the leech next to the puncture, and it promptly clamped on and started sucking. The leech swelled up as it siphoned off the pooling blood until, after a few hours, it fell off, engorged and satiated. After a few more cycles with fresh leeches, the bartender’s finger had turned from purple to a healthy pink.

The bartender was lucky in this case. “After about a week or so of treatment, she was able to leave with an intact finger, without surgery,” Levine says. She became so invested in her treatment, Levine recalls, that she even named her leeches — choosing standard male names, like Michael and Bob.

More than a century after most physicians stopped using them in their everyday practices, leeches are back. The Food and Drug Administration approved them as “medical devices” in 2004. Their primary use is in reconstructive surgery and microsurgery to help return blood flow to severed veins.

Reattaching fingers is a good example. With small, tenuous veins and more robust arteries, newly reattached fingers can easily fail due to poor circulation. Blood flow can become congested and eventually stop altogether, causing the digit to die. Leeches “can help the finger to bleed and get off the excess of blood that the venous system can’t quite handle,” Levine explains. Leech saliva also contains hirudin, an anticoagulant that helps the blood keep flowing even after the leech fills up.

Now, almost ten years after the FDA approval, scientists are exploring some additional clinical uses for leeches, primarily for conditions that limit blood flow, like arthritis. But questions of safety and effectiveness remain for the uses that go beyond what the FDA has approved, and using leeches for more treatments may mean trouble for the leeches themselves, since many species are already threatened.

Leech research “is on the rise,” says Paul Cherniack, a professor of geriatric medicine at the University of Miami who wrote a paper on the use of leeches. “People are definitely becoming more aware of it.”

Healers have been using leeches for thousands of years. Ancient Indians, Mesopotamians, Egyptians and Greeks used them for bloodletting, which was supposed to treat ailments ranging from skin conditions to cancer. But many of those supposed treatments ended up doing more damage than good, and by the late 19th century bloodletting was widely discredited.

Biomedical researchers never completely lost their fascination with leeches, however. “They’re interesting, they’re different and they’re ancient,” says Iain Whitaker, a professor of plastic and reconstructive surgery at Swansea University in Wales. There are more than 700 species of leeches, all carnivorous, ranging in length from a few hundredths of an inch to greater than 18 inches. Their jaws consist of three layers of blades, making the distinctive Y-shaped incision they make in the flesh of their prey essentially painless.

Part of why leeches have been involved in medicine for so long is the unique cocktail of medically useful compounds they release while feeding, says Joerg Graf, a molecular biologist at the University of Connecticut in Storrs. “[Leeches] have a suite of chemicals that they release in their saliva when they bite,” including anticoagulants and painkillers, he notes.

In recent years, scientists have studied everything from leeches’ genetic makeup to their neurological structures and gut bacteria. “Leeches are a really interesting — and simple — model organism,” Whitaker says. “You can study them from lots of interesting angles.” They have 32 brains (one in each segment of their bodies), and their primitive neural structure can answer questions about how messages are transmitted in our own brains. Meanwhile, microbiologists study how their bacteria can affect humans, and their saliva contains “the most potent anticoagulant known to man,” Whitaker says.

The research is paying off with some new medical applications, some of which are already being used in other countries, Graf says. Several studies in Germany have found that leeches could help to reduce pain and joint stiffness in patients suffering from osteoarthritis of the knee. Other European studies have concluded that the painkiller in leech saliva is effective in treating rheumatoid arthritis, which can affect patients’ hands and feet. One 1998 study from India even found promising results in using leeches to treat varicose veins, but little work has been done since to evaluate it.

While many leech-related studies are now being conducted, many medical professionals are not yet convinced that these new treatments are effective, according to Whitaker. The problem is that leech studies don’t include control groups that receive placebos – it’s hard to pretend to put a leech on someone – and thus are often regarded as unreliable, Graf says.

Some experts believe that even more uses for leeches are on the horizon. Mark Siddall, a curator who studies leeches at the American Museum of Natural History in New York City, thinks that their anticoagulants could be beneficial. Hirudin, the anticoagulant in leech saliva, doesn’t present most of the issues that some other naturally occurring anticoagulants do. Heparin, for example, an anticoagulant originally found in liver cells in dogs, can sometimes cause a serious condition called heparin-induced thrombocytopenia in humans, which can lead to internal bleeding.

Developing anticoagulants from hirudin has been a sort of “holy grail” for pharmaceutical companies, says Levine, the Bellevue physician. Some that have already been developed include Desirudin, used to prevent deep vein thrombosis, and the now-discontinued Lepirudin (production stopped due to expirations in pharmaceutical contracts). Some companies even sell a topical cream based on hirudin that is supposed to treat scars, bruises and other minor injuries by distributing blood flow more evenly.

Although they can do a lot of good, leeches can still pose a threat to humans. A particular species of the bacteria Aeromonas lives in their gut, on their exterior and even in the water the leeches inhabit, says Connecticut’s Graf. It helps the leeches to digest blood but is “capable of setting up a serious tissue infection,” Siddall says. To counteract this, surgeons who use leeches prescribe antibiotics to their patients, but Aeromonas is becoming resistant to some antibiotics, Graf notes. He and other researchers are delving into how the bacteria are building this resistance so they can combat it in the future.

Humans aren’t the only ones at risk when they use more leeches. Siddall is concerned that using leeches in too many different treatments could further threaten various species that are already at risk. Without government regulation, he says, “leeches might be extirpated in the wild.” On the other hand, Whitaker notes, the leeches used in medical practice today are raised in labs by specialized companies and carefully shipped to hospitals and medical centers. “It’s never going to get to the state like in the late 19th century where they used hundreds of millions of leeches per year,” Whitaker says.

Still, leeches have certainly “captured the public imagination,” Whitaker notes. Practitioners and researchers may be among the most captivated — the respect is palpable when they discuss them. “They’re not as ugly as they seem,” Graf says. “When you have the right light, they have beautiful pigmentation.”

Levine, who has been using leeches in his medical practice for years, agrees. “They’re very docile. They’ll cuddle you, they’ll integrate very well with you if you let them,” he says. “They are performing a very unique function, you’ve got to respect it.”