As if you couldn't tell by the title, this is a node with icky subject matter; if you are disturbed by the thought of larvae crawling over and through your torn flesh, wriggling, squirming, feasting on your tissues - well, too late: you're thinking about it already. So read on, and learn about one of the more compellingly revolting practices in medicine.
Myiasis is the inadvertent infestation of wounds with maggots. Nowadays, modern hygiene and the sterilization of medical equipment mean that myiasis is not a condition that normally afflicts people in the western world. But for centuries, myiasis was a frequent accompaniment to injury. Maggots of certain types will eat necrotic, or dead, tissue while sparing living tissue. Before the days of modern medicine, it had been observed that myiasitic wounds tended to actually heal better than those without maggots. This was known to the Maya and was observed in the sixteenth century in Europe. Battlefield surgeons saw many cases of myiasis, since the filth of battle tended to mean that many wounds were colonized by maggots. Those soldiers lucky enough to have maggots in their wounds were less likely to die of their infections, which led to early experiments in the United States during the Civil War. This prompted William Baer's investigation of maggot therapy at Johns Hopkins University.
As noted above, maggot therapy lost most of its cachet when antibiotics entered common use in the wake of World War II. They were used occasionally but rarely between the mid 1940s and 1989, when physicians in California investigated their use more heavily. Since maggots could occasionally spare limbs that might otherwise have been amputated, it seemed reasonable to consider them as a mainstream treatment for certain types of injuries - notably, hard to heal wounds like bedsores, chronic leg ulcers, and foot ulcers related to diabetic neuropathy. They are only used in open wounds, as the things need air to avoid suffocation. Plus, I don't think it'd be a good idea to invite the suckers to crawl around inside a closed abcess.
Maggots work by consuming the dead tissues that house infection, while secreting proteolytic (protein-destroying) enzymes and other chemicals that actually kill a wide range of bacteria, including the very common Staphylococcus aureus (of particular interest nowadays is their use in wounds infected with MRSA, methicillin-resistant Staph aureus). The "micromassage" of wounded tissue is believed to stimulate the growth of new tissue, and proteins released by maggots actually promote wound healing. Nowadays, over 2,000 practitioners worldwide use maggot debridement therapy.
Maggots are purchased in single-use vials and applied directly to wounds, with semi-permeable dressings that prevent their escape while permitting drainage of liquified necrotic tissue. A single cycle lasts 48 hours, after which the maggots are removed - but some wounds require several treatments before they are fully debrided. Medical maggots are larvae of the green blowfly, Phaenicia sericata (a.k.a. Lucilia sericata). They are carefully raised in a sterile environment to ensure that they don't transmit disease to patients. This species is one of the ones that doesn't consume living tissue (while other types will eat indiscriminately and can't be used therapeutically). Experiments have been performed with other species of maggot, but the green blowfly is the only type in mainstream use.
A vial of maggots contains around 2,000 eggs, of which 500 to 1,000 should have hatched into little baby maggots. They should be used as soon as possible, no more than 24 hours, to insure viability. They should be removed after 48 hours of debridement, as they become full and no longer consume tissue. They should not be used on patients with severe, rapidly advancing infections, as surgery is probably warranted and the wound cannot be observed when covered for maggot debridement. They are not appropriate as a primary therapy for bone or tendon infections, nor should they be used in patients with severely compromised circulation or around necrotic blood vessels (as they could rupture). Finally, they should not be used in sterile body cavities - don't stick 'em in your eye, your upper gastrointestinal tract, or your respiratory tract.
They should be removed promptly when the two day cycle is over, although it takes several more days for them to pupate, and even then they do so in dry, hidden places rather than in wounds. When the dressing is removed, they try to escape on their own and merely need to be picked up with wet gauze. Very heavy infestation of maggots in animal wounds is known to cause systemic problems, particularly due to high levels of ammonia in the blood, but this is not a problem with usage at normal medical levels. The most common side-effect of maggot therapy is pain, which may be related to the pH of the wound as it's debrided. Analgesics can be used if necessary, and should the pain become intolerable it generally clears up immediately upon removal of the maggots.
As the superiority of maggot therapy to more conventional treatments has been more widely understood, maggot debridement is becoming more and more popular. Many patients are uncomfortable with the idea (as, no doubt, are many doctors) and this has slowed its acceptance but most patients who are treated are satisfied with the results, and in many cases it can clear up infections that had previously resisted all treatment.
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