THE WORM HAS RETURNED

Could lowly creatures provide a cure for breast cancer or help in the fight against Aids? Norman Miller reports on new breakthroughs

Once upon a time, when you wanted a bit of flesh-eating or bloodsucking you had to venture to places like New Guinea or Transylvania. Now, Wales will do nicely. For, in Swansea and Bridgend, the principality has two of the world's major centres of what has been dubbed "biosurgery".

Biosurgery centres on the use of live animals to treat medical problems where drugs or normal surgery have failed. In particular, it owes a debt to two animals usually regarded with disgust - leeches and maggots.

The first reported medicinal use of leeches was by Nicader of Colophain in 200BC but it was Galen (129-199AD) who gave their use an early medical spin with his "humoral" theory of disease based on the idea that the body contains four "humours" (blood, phlegm, and yellow and black biles) which, when out of balance, result in disease. Leeches, by removing "bad" blood, restored the balance in the treatment of everything from polio to laryngitis.

By the mid-1800s demand for leech treatment was so widespread that an estimated 30m were shipped annually from the leech powerhouse of Germany - an appropriate choice of country in hindsight since the bite mark of the medicinal leech, Hirudo medicinalis, is the spitting image of the Mercedes Benz symbol. However, as modern concepts of medicine developed, the use of leeches was damned as quackery, and consigned to the footnotes of medical history.

In the early 1980s, however, the leech came back into play in the field of microsurgery in the treatment of venous insufficiency. This complication occurs in tissue that has been reattached to the body - fingers torn off in accidents, for example, or skin grafts. Microsurgery can sometimes manage the delicate task of reconnecting the blood vessels of the reattached tissue, but the whole procedure may fail if poor circulation or blood clots follow. Enter the humble leech.

The case that did most to bring about the renaissance of this remarkable bloodsucker occurred in 1985, when a boy in Boston had his ear torn off by a dog. A delicate 12-hour operation to reattach it saw the Harvard Medical School team reconnect some of the ear's circulation, but this was not enough. Within days, blood clots threat-ened its survival, despite treatment with modern anticoagulants combined with blood-letting. It was then one of the surgeons decided to turn to the leech, an old friend from field work as a wartime surgeon in Vietnam. In peacetime Boston, they proved equally effective; two dozen leeches worked in rotation over a week to suck blood through the boy's ear. More specifically, the anticoagulants in the leech' s saliva kept the blood flowing for up to 10 hours, after the animals themselves had dropped off following 20-minute feeds in which they gorged themselves to four times their unfed size. The establishment of a healthy blood flow allowed the boy's body time to reweave the tapestry of veins and re-establish normal circulation, and the ear was saved.

Since then, the technique has been used many times worldwide with equal success, and it is a British company, Biopharm, that has led the way in promoting leech therapy, and which now exports medicinal leeches to 27 countries from its base near Swansea.

Biopharm is the brainchild of the world's leading leech expert, Roy Sawyer, who was first bitten by the leech bug as a boy growing up near the swamps of his native South Carolina. Sawyer calls the leech "a living pharmacy", but lack of interest from drug companies forced him to go it alone in setting up the world's first modern leech farm, with the motto "The Biting Edge of Science". Sawyer has likened the breeding of both the medicinal leech and the company's other bloodsucker, the giant Amazon leech, Haemanteria ghilianii, to growing orchids - a comparison which doesn't seem far-fetched when you see the gracefulness of the leeches as they swim sinuously through their tanks looking like the fronds of a fern. The Amazon leeches even have a liking for classical music, with Bach a particular favourite.

Though Biopharm has found fame as a supplier of medicinal leeches for biosurgery (2,000 are born every week), the company now focuses as much effort on the pursuit of the pharmacological treasures to be found in the saliva of both of their leech species. So excited was Sawyer by the biochemical potential of the giant Amazon leech - whose existence he was only alerted to after reading an 1846 Italian medical paper - that he personally led the gruelling expedition to the jungles of French Guiana which provided the 35 specimens of this rare giant (it can grow up to 18in long) from which Biopharm has bred thousands of descendants.

Biopharm now leads the way in the biochemical exploitation of the leech, though the first advance in the field was made as the medical use of leeches began to fade in 1884, when JB Haycraft isolated a naturally occurring anticoagulant from leech saliva, which he named hirudin. But it was not until 1955 that hirudin could be completely identified and its workings understood.

When the skin is punctured, the body stems the loss of blood by making it coagulate. However, coagulating blood is the last thing a hungry leech wants, and the medicinal and Amazon leeches have evolved formidable chemical arsenals to ensure happy mealtimes.

Biopharm researcher Bob Wallis likens coagulation to a "cascade of enzymes", and the leech has evolved an array of chemicals to act at different points in the cascade. The 19th century discovery, hirudin, has now been joined by bufrudin, ghilanten and antistasin to name a few, but these anticoagulants are just part of the leech's weaponry. Perhaps the most excitement has been generated by products such as hementin, a gift from the Amazon leech, which is an enzyme that actually dissolves clots rather than simply stopping them forming - a property which holds much promise in treating cardiovascular disease, strokes and even arthritis and glaucoma.

In fact, Biopharm's researchers have isolated over 50 chemicals from the saliva of their two leech species, of which 10 are already the subject of patents. The spectrum of uses covered includes anticoagulants, clot- busting enzymes, vasodilators which prolong bleeding following a bite, chemicals which help spread anticoagulants in the wound, and possibly even a local anaesthetic that protects the feeding leech from discovery, though this is still disputed. Other useful chemicals extracted from leech saliva include calin and ornatin which block the formation of platelets (the first thing that happens in a cut), and protein-dissolving enzymes such as eglin.

The other animal star of modern biosurgery has a far more direct approach to getting rid of tissue - eating it. Maggots may arouse almost universal disgust (except perhaps among angl-ers), yet, like leeches, they have a long medical history.

Bridgend is home to the NHS Surgical Materials Testing Laboratory where director Stephen Thomas is updating an ancient approach to the treatment of infected wounds. The ability of maggots to clean out bad tissue and enhance wound healing has been recognised for centuries. Medical officers during the American Civil War are believed to have made the earliest therapeutic use of "surgical maggots". Early pioneers recognised the maggots' greatest quality - that they only ate dead or infected tissue, leaving healthy tissue alone. Their observations were confirmed during World War One and so-called larval therapy became common in American hospitals of the 1930s in treating chronic or infected wounds. There were even medical reports at the time of cases of inoperable breast cancer where larvae removed the malignant tissue, though surprisingly these do not seem to have been followed up.

Experts believe that the larvae combat wound infection by ingesting harmful microorganisms which are then destroyed in their gut. There is also evidence that the maggots exude antibacterial chemicals such as allantoin, while larval therapy also seems to stimulate the production of healthy granulation tissue. But with the advent of widespread use of manufactured antibiotics, the practice of larval therapy declined in the 1940s. However, the emergence of an increasing number of antibiotic-resistant bacteria in recent years has prompted clinicians to reconsider nature's own more direct approach, and the work of the SMTL is in the forefront of developments.

In particular, the unit has pioneered the breeding of sterile larvae, at a stroke dealing with the major threat of infection which was present in past use of maggots. Raw liver in the unit's "fly room" is the starting point of a breeding process which is like one of Damien Hirst's early pieces only more hygienic. Eggs from greenbottles, Lucilia sericata, are collected on the liver, then cleaned with similar equipment to that used for producing sterile pharmaceutical products. After hatching, each batch of larvae is then tested for sterility before ending up in one of the small plastic flasks which the SMTL sends out to 50 hospitals in Britain at a cost of around pounds 50 for a container of 200 maggots.

For clinical use, the 2mm-long larvae are introduced into the wound and kept in place using a dressing system designed to fit the particular wound under treatment and prevent the larvae from escaping. The dressing is also designed to protect intact skin from the potent enzymes produced by the larvae to break down flesh for digestion. The number of larvae used depends upon the size of the wound and the amount of dead or infected tissue, with numbers ranging from half-a-dozen up to several hundred. An average dose of larvae can digest around 14 grams of dead tissue a day. The maggots are generally removed after three days when, depending on the condition of the wound, a fresh batch can be added. According to Stephen Thomas, the only downside of larval therapy seems to be a tickling sensation experienced by some patients, and he is quick to scotch fears of maggots staying in the wound to breed, since mature larvae must leave the wound to pupate.

Surprisingly, perhaps, patients seem remarkably tolerant about a treatment which might be expected to arouse strong reactions. Medical staff are even more affirmative with favourable opinions on larval therapy expressed by over 90 per cent in one recent US survey.

While raw liver is a starting point for maggots, it is an end point for a third animal which is making medical waves - the liver fluke, Fasciola hepatica.

Immunologists are on the trail of this parasite, which was first recorded in humans in the 17th century.

The parasite is acquired when humans eat contaminated vegetation. Once inside the intestine, the fluke burrows through the intestinal wall, then moves to the liver where it remains for several weeks, causing extensive perforations and haemorrhaging, before migrating to the immunologically safe environment of the bile ducts, where it matures and releases eggs which pass out in faeces to cause further con- tamination and begin the process again.

But how does the fluke manage to survive the attack of the body's immune response which it triggers on its journey, and its lengthy and damaging stay in the liver? This is the question which is being tackled by researchers such as John Dalton of Dublin City University, with the answer holding out the promise of powerful insights into the workings of the immune system and the creation of new immunological drugs.

Research by Dalton and others suggests that the fluke survives the body's attack by secreting chemicals called proteases around itself which protect it from the immune system as it migrates, and which, in fact, counter- attack the system. The antibodies which the body sends against its foe are Y-shaped structures whose arms bind to the invader and "tag" it. Immune effector cells recognise the bound antibody and they bind in turn to the stem of the Y. These cells then release toxins such as nitric oxide which kill the invader. However, the fluke's protease weapon-ry strikes back by breaking the bridge between the binding top of the Y on the antibody and its stem. This means the immune effector cells cannot bind to the antibody and kill the parasite.

The fluke can also call on another tactic to win its battle with the immune system, which involves not so much defeating it but controlling it. Although antibodies come in different classes, they are all produced using just two kinds of what are called Thelper cells, TH1 and TH2. The type of Thelper cells that are stimulated following an infection will determine the type of antibodies and immune effector cells produced, but they will all involve either a TH1 type response or a TH2 one. If an invading organism has adapted to cope with one of these better than the other, then the ability to make the body trigger the desired response would be a powerful defence - a bit like a football team being able to choose Accrington Stanley as its opposition rather than Manchester United. Research has shown that the liver fluke induces a TH2 type response, which means it has to face attack by eosinophils rather than the more active attack by macrophages which is associated with TH1 response. Dalton stresses, however, that the parasite is performing a delicate balancing act. "It is not in the parasite's favour for survival to either kill or be killed by its host," says Dalton, "but to parasitise it until it has had a chance to reproduce."

This balancing act is like a set of scales with the liver fluke's immuno- controlling chemicals on one side and a bonanza of immunological drugs on the other. Specific chemicals, such as the fluke's protease secretions, can either suppress the body's immune response or drive it one way or the other (modulation). "If we can figure how they do this," says Dalton, "or why we respond one way or the other, then we could produce drugs to modulate the immune system ourselves to fight diseases like cancer, to which we do not take the appropriate immune response to eliminate the malignant cells."

This same approach may be extended to other human pathogens, such as malaria and Aids. In the case of HIV infection, Dalton points out, the progression of the infection to full-blown Aids correlates with the gradual conversion from a TH1 type response to a TH2 type. "Curing Aids wouldn't be as simple as reversing this changeover," he says, "but manipulating the immune responses will certainly be a component of treatment if a vaccine could be developed."

Our own response to these revelations should perhaps be to acknowledge Shakespeare's warnings about judging by appearance. For, whatever feelings they inspire, this trio of unlovely animals are holding out nothing less than the promise of medical gold. !

YOU TASTE SO GOOD

"They would feed for about 15 minutes and when they were full they dropped off - but if one fell on my nightie I tended to scream"

Alice Plunkett, whose re-attached ear was saved by leeches

"We first ask them if they like animals. Then we work up to leeches."

Dr Felix Freshwater, Cedar Medical Center in Miami

"There was a sort of tickling sensation at times, though it wasn't unpleasant in itself. But I did have to try hard not to feel what was causing it."

Patient describing larval therapy

"I have suffered intense agony from my ulcer for two years. Now the pain is almost negligible. Where previously I overdosed with painkillers to little effect, I now hardly need them at all."

Larval-therapy patient