Lending a hand in the hospital (Image: Sipa Press/Rex Features)

THE cardboard box marked “Emergency Medical Shipment” thumps down on Lillian Jackson’s desk in the supplies department at Vanderbilt University Medical Center in Nashville, Tennessee. Inside she finds a sealed plastic bag of water in which dozens of small black creatures are happily swimming around. Leeches, again! Without hesitation, Jackson sends the creatures to the hospital’s trauma unit, where nurse Rene Kopp takes charge. Over the next few days, Kopp will apply the leeches to chosen patients – to suck their blood. “We’ve been doing it for years,” says Jackson.

Leeches have indeed been used in medicine for years – for millennia, in fact. They were once believed to remove illness-causing fluids, or “humours”, from the blood. In reality they probably had little effect, and by the late 19th century such bloodletting had fallen out of favour. In the early 20th century, however, it occurred to surgeons that the slimy annelids might have a useful medical role after all. Leech bloodlust, they figured, was just the thing to help treat a dangerous complication after surgery to reattach torn or severed body parts such as fingers, ears or flaps of skin. Excess blood can collect in the reattached part, which, if left untreated, can cause tissue death and even be life-threatening.

Leeches are perfect for relieving “venous congestion”, as this phenomenon is known. “The leech’s primary role is to act as a vein,” explains Richard Miller, medical director of the Vanderbilt trauma unit. In addition to the blood it consumes, the leech injects chemicals that stop blood clotting, which keeps blood flowing from the wound after the beast leaves. …