by Prof. Chris Appleton
After being one of the mainstays of medical practice in Europe since the time of Hippocrates, use of the medicinal leech, Hirudo medicinalis, fell into disrepute in the second half of the 19th century but it has made a dramatic comeback in recent years! So popular was the use of H. medicinalis for draining blood ("leeching") as a cure for different kinds of disease, that over-collecting for hundreds of years in western and central Europe drove the species almost to extinction. Not surprising in view of the old hospital records cited by Adams (1988) that during 1829 and 1836 for example, between 5 million and 6 million leeches were used annually in hospitals in Paris, drawing nearly 85 000 kg of blood from patients each year!
There are many similar records of incredible numbers of medicinal leeches being used across Europe. Indeed individual patients were often bled by 50-60 leeches at the same time and on consecutive days! The effects of this exploitation are seen in many parts of Europe today where the medicinal leech is still rare and was included in the "near threatened" category in the IUCN's 1996 Red Data List.
The "new found" use for H. medicinalis is in plastic and reconstructive surgery! These annelids have become valuable tools for saving transplanted skin flaps or grafts that have become congested with blood, i.e. the blood hasn't drained away because the necessary capillaries have not joined or formed as the case may be. This will cause the death of the flap - and happens in about 10% of procedures. Enter the leech! If hungry leeches are allowed to suck up the excess blood and so relieve the congestion and accompanying swelling - the flap can often be saved.
A single leech will remain attached for 30-40 minutes and suck up 10-15ml of blood in that time. Their value lies in the fact that their saliva, which is introduced into the tissue as they bite, contains an anticoagulant, hirudin, which prevents clotting and therefore allows fresh, oxygenated blood into the wound area until capillaries have grown and proper circulation is established. In this way, leeches have helped save what in surgical jargon are called "pedicled skin flaps" on many different parts of the body, e.g. ears, noses, lips, eyebrows, scalp, fingers, hips and legs. In South Africa however H. medicinalis is not available and has to be hurriedly imported when needed - often for an emergency.
There are "leech farms" in the UK, Europe and the United States who will supply leeches but at considerable cost and of course a delay of a day or two which might make the difference between saving or losing a flap. We need a local source of supply and we have several indigenous species of blood-sucking leeches to choose from. One of these, Aliolimnatis buntonensis, was investigated and tested at a Durban hospital as a local alternative. It was successful! This leech is common in the lakes and marshes from KwaZulu-Natal northwards into Mpumalanga and Northern Province and is one of seven southern African species of large, brown leeches with alternating dark and light stripes running down their backs.
It grows up to about 85mm in length and can be recognized by its central stripe being light and not dark brown. They swim well and while hippos are probably their natural hosts, they do not hesitate to attack people if they get the chance. All bloodsucking leeches have a set of three sharp jaws with which they puncture their victim's skin leaving marks that resemble the Mercedes Benz star and a powerful, muscular pharynx to suck up the blood as it oozes out. In addition the intestine has many branches each of which fills with blood, allowing the leech to take in a bloodmeal large enough to last it many months.
There are however problems associated with the use of leeches in this way. One is the possibility that, if used on more than one patient, they could transmit pathogens like the hepatitis B virus and HIV from one patient to another. Research done on A. buntonensis in Durban by Glenn Wilken suggests that if a leech is fed on hepatitis B +ve blood, the virus may persist in its bloodmeal for several months while digestion takes place. Although we know nothing about the fate of HIV under such conditions, such "mechanical" transmission will be avoided by the general policy of using a leech only once. Another problem is that probably all blood-sucking leeches harbour symbiotic bacteria, Aeromonas hydrophila, in their intestines.
This bacterium helps with the digestion of its bloodmeal and also produces an antibiotic that limits the growth of other bacteria such as those that cause damaged tissue to become necrotic and die. It has been argued that allowing an A. hydrophila-infected leech to feed on a patient may expose that patient to infection by this bacterium too. Indeed cases of A. hydrophila infections have been reported in people after undergoing microsurgery in which leeches were used. The best way to avoid infections of this kind from A. buntonensis is to apply antibiotics such as gentamicin, amikacin, chloramphenicol and tetracycline to the wound immediately after the leech has released itself.
To date only wild-caught A. buntonensis have been used in microsurgery South Africa. It would be ideal if it could be bred in captivity, especially since leeches are often needed in emergency situations when time is of the essence. An example occurred two years ago when a small boy was caught in a combine harvester in the KwaZulu-Natal midlands. Both his feet were severed and although one had been re-attached successfully, the other was failing. Leeches were seen as the best option for saving it but unfortunately none were available. As far as I know, there are no laboratory colonies in the country.
An attempt to do so in Durban was partially successful but showed that we do not know enough about the animal's reproductive biology to set up breeding colonies. More research is required on the breeding behaviour of A. buntonensis and also on methods for artificially feeding juveniles and discarded adults - each leech should only be used once and then used for breeding purposes. We know that A. buntonensis breeds in summer when water temperatures are around 25°C. Gravid adults crawl out the water at night to lay cocoons containing an average of about 14 eggs each beneath vegetation on damp mud. Laboratory observations suggest that A. buntonensis is long-lived but grows slowly, its weight increasing 2.9 - 3.8 fold after a bloodmeal. Analysis of data from laboratory feeding experiments over 9½ months allowed Glenn to estimate that it will take about four years for A. buntonensis to reach the minimum suggested weight of 2.4g for use in microsurgery (H. medicinalis takes about 2½ years). This may however be an over-estimate since the interplay between the leeches' breeding cycle, nutritional state and temperature is complex and needs to be investigated before the optimal conditions for establishing breeding colonies can be determined.