Maggot Debridement Promotes Healing of Long-Standing Wounds

Daniel M. Keller, PhD

September 28, 2011

September 28, 2011 (Chicago, Illinois) — Maggots are an effective, low-cost salvage option to debride poorly vascularized, infected wounds in patients with diabetes, especially when vascular remediation is not possible, Lawrence Eron, MD, infectious disease consultant at Kaiser Moanalua Medical Center and associate professor of medicine at the John A. Burns School of Medicine of the University of Hawaii in Honolulu, told delegates here at the 51st Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC).

Dr. Eron said that in addition to debriding nonviable tissue, maggots secrete bacteriostatic substances that help eradicate infections in conjunction with antibiotics. He said his talk involved a medical device, "and the device is the maggot."

Dr. Eron said that diabetic limb infections are difficult to treat with antibiotics in part because of vascular insufficiency. Maggot debridement therapy (MDT), using the larvae of the green blowfly (Lucilia sericata), not only removes necrotic tissue without affecting viable tissue but also stimulates the formation of granulation tissue.

Dr. Eron and colleagues used MDT to treat 37 patients with diabetes with complex wounds complicated by diabetic comorbidities. "In some cases, these wounds had been present for as long as 5 years and had failed multiple attempts at treatment," he said. The original wounds were abscesses, infected ulcers, and osteomyelitis with very narrow fistula tracts.

MDT consisted of applying 50 to 100 maggots to a wound, which were covered with nylon mesh fabric (similar to pantyhose) and then removed after 2 days. Clinicians then reapplied more maggots, and the cycles were repeated as necessary (median, 5 cycles; range, 1 - 30 cycles). Maggots were commercially obtained from Monarch Labs at a cost of just under $100 per treatment with 200 maggots.

The researchers defined a successful outcome as elimination of the infection, complete debridement of devitalized tissue, formation of robust granulation tissue, and greater than 50% closure of the wound. "The maggots will not totally heal the wound," Dr. Eron said. "We need other, further methods to heal the wound."

Of the 37 patients, "three quarters, roughly, achieved successful outcomes. The majority had Gram-positive infections. The Gram-positive infections seemed to do better than the Gram-negative anaerobic infections," Dr. Eron reported. The numbers were quite small, however, and a few wounds were culture-negative.

Representative Gram-positive organisms were methicillin-resistant Staphylococcus aureus, methicillin-sensitive S aureus, and group B streptococci. Patients were treated with appropriate, commonly used antibiotics, depending on the infecting organisms.

Failures occurred in patients with severe peripheral vascular disease with narrow fistulae that were not mechanically accessible after they healed after a single treatment in 3 patients with osteomyelitis, with bleeding from wounds (n = 2), or with excessive inflammation around the wound (n = 1). Pain limited treatment for 1 patient, but Dr. Eron said 5 or 6 patients responded well to acetaminophen for discomfort.

"The rest of the patients seemed to acquire, even with their peripheral neuropathy and numbness, some degree of sensation and would feel a creepy, crawly sensation, which they didn't object to," he said. "In fact, they appreciated [it] when they were dealing with anesthetic feet prior to [MDT]. It's an interesting phenomenon, and probably is worthy of investigation."

He warned that MDT is contraindicated in patients with coagulopathies and in patients with large blood vessels near their wounds.

Diabetic wound healing is hampered by a number of factors, not the least of which is vascular disease. Dr. Eron told the audience that MDT "allowed many of these patients — three quarters of them — to be ready for a second phase" of wound treatment, "and in many cases it averts amputation." He compared the median cost of about $500 for MDT to the cost of an amputation, which can be $65,000.

He noted that patients with peripheral vascular disease also have generalized vascular disease, so averting an amputation may allow a patient to live out his or her life with limbs intact. In the study, 5 patients died, usually from heart disease, during follow-up after successful MDT.

These investigators saw, as have others, an apparent antimicrobial effect from the maggot therapy. "It may stimulate defensins, which are part of our innate immune system," Dr. Eron said. "There seems also to be an angiogenesis type of effect because in many cases it converted dry wounds into moist, healthy wounds...and finally it seemed to stimulate granulation tissue."

In an interview with Medscape Medical News, session moderator Catherine Bennett, PhD, chair in epidemiology and head of the School of Health and Social Development at Deakin University in Melbourne, Australia, referred to MDT as "biosurgery" that gets around the problem of antibiotic resistance in the infecting bacteria. "You're actually looking at a very targeted, selective approach to tissue removal...completely a different approach to trying to actually treat the organism causing the destruction in its own right," she said.

In light of some patients refusing amputation of a limb with an infected, nonhealing wound when it is clearly indicated, Dr. Bennett said, "If there aren't ways you can treat it with standard therapies or in ways that the patients would tolerate, then this is obviously providing a new insight."

She speculated that if the evidence for MDT continues to be good, perhaps practitioners and patients will be persuaded to use it earlier and not pursue ongoing, futile treatments, especially as the downside risks appear minimal. "It doesn't seem to have any complications in the same way as even other standard drug therapies," she said. "If there's good indication that it's going to give you good outcomes, then pushing it back earlier would avoid the delay to effective treatment."

In addition to the contraindications that Dr. Eron mentioned, the package insert for commercial, by-prescription-only maggots warns that pain and discomfort are possible adverse effects, as well as potential allergic reactions in patients who are allergic to fly larvae or the brewer's yeast or soy proteins contained in the nutrient medium that the blowfly eggs are shipped with.

The study received no outside support. Dr. Eron and Dr. Bennett have disclosed no relevant financial relationships.

51st Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC): Abstract L-967. Presented on September 18, 2011.