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Return of the leeches!

Philippa Jefferies draws out the truth behind the leech's comeback in modern medicine

Usually, when someone mentions leeches and bloodletting, images of medieval physicians forcing leeches on their patients for any ailment are the first to jump to mind. Whilst it is common knowledge now that this is probably not the best way to relieve every symptom, leeches aren’t without their uses in modern medicine. In 2004, the FDA approved the sale of leeches for medical use in the USA and they are vital in many surgeries - particularly skin grafts and reconstructive surgery.

They were first used for medicinal purposes in ancient Egypt, about 2,500 years ago, and became a popular remedy for the Ancient Greeks and Romans as well. Bloodletting, the removal of blood for medicinal purposes, was used to balance the humours: blood, phlegm, black bile, and yellow bile. It was thought that an imbalance of these was the cause of illness, therefore getting rid of some of the dominant humour (blood) could be a cure. Leeches were popular through to the start of the 20th century when they stopped being used as frequently, as antibiotics and other treatments became prevalent. However, they made a comeback in the mid-20th century as their specific benefit in surgeries and treatment of vascular diseases became apparent.

So what service can leeches provide that modern medicine can’t? It has all to do with the ‘saliva’ the leeches produce when they are drinking blood. The substance contains strong anticoagulants, i.e. blood thinners, which stop the blood clotting or congealing within the leech. This is useful for them as they can then retain mobility after feeding.

How does this help us humans? Well, one particular area in which leeches are frequently used is maintaining blood circulation after reconstructive surgery. Arteries are relatively simple to attach, due to their thick walls, however the same cannot be said for veins, which are difficult to suture, especially when they have been damaged. The circulation through the newly joined veins can become impaired, resulting in the congestion of the blood flowing through the veins. Without a good flow of blood through the tissue, the new appendage could be lost. This is where leeches come in. They are there to essentially buy time for the veins to open up and proper circulation to be restored. The leech creates a puncture wound, which is left to bleed. Their ‘saliva’ dilates the blood vessels and keeps the blood flowing, preventing any congestion or clotting. Leeches are also preferable for this kind of treatment as the small Y-shaped mark they cause usually heals quickly, without leaving a scar.

Ken Dunn, a consultant at Manchester Burns and Plastic Surgery Service, told BBC News “The treatment simply buys time for the venous drainage to open up and improve, usually 3-5 days. If this is not done the tissue will die from that congestion of blood” and that "On average, the tissue bleeds about 10 times the volume of blood that the leech actually removes to feed on, making it a very efficient and effective treatment.”

Leech therapy is also gaining popularity. The mixture of substances in the leech's saliva can be used to help treat vascular disease, by promoting blood flow to various areas, as well as a whole range of other conditions from cardiovascular diseases to arthritis and ear problems. It is used often because it has a lower risk of side effects than other treatments.

So despite their off-putting appearance, it seems leeches aren’t leaving hospitals anytime soon.

From Issue 13

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