Heidi A. Jeske, CO
University of California, San Francisco
San Francisco, California
Maggot Debridement Therapy (MDT) is an ancient wound care modality. The first documentation of maggots debriding a wound was from Ambroise Pare following the battle of St. Quentin in the 1500's. While working with soldiers who remained on the battlefield for days after being wounded, military surgeons in Europe and the United States during the Napoleonic and Civil Wars observed that maggots destroyed only dead tissue (1). MDT was used extensively in the United States during the 1930's and 1940's but lost popularity with the introduction of antibiotic therapies (2). Use of MDT has steadily increased over the past decade and new clinical research studying the efficacy and applicability of this treatment is being published in the diabetes management and wound care communities. In 2004, the FDA approved production and marketing of maggots as a medical device (3).
The primary goal of any approach to debridement is to eliminate all slough and necrotic tissue from the wound in order to change a chronic wound into an acute wound which can then be treated by other modalities. Clinical studies indicate that MDT accomplishes these goals in a shorter time period and with less antibiotic usage than with conventional wound treatment (4, 5, 6). In a study by Sherman, statistical analysis demonstrates that the only significant factor related to change in necrotic tissue when comparing conventional versus MDT is the treatment (4, 5). Although rate of wound closure once debridement is complete is the same as in conventionally treated wounds, MDT allows the closure to begin in at an earlier time in the patient's course of treatment (4). Maggot Debridement Therapy is a cost-effective and useful tool in wound care.
Phaenicia (lucilia) sericata (green blowfly larvae) are the species of maggots used for MDT. The "medical maggots" are bred in a sterile environment and shipped in vials to the clinical site. The larvae are two millimeters long at the time of hatching and feed only on necrotic tissue and fluids in a wound. The maggots can be applied to any type of wound with necrotic or fibrous tissue that requires debridement, regardless of etiology or whether there is infection present. It is helpful for the wound care team to perform a sharp debridement to remove eschar from the wound as it is more difficult for the larvae to penetrate this thick tissue. If the wound is dry, pretreatment with a hydrogel dressing to introduce moisture will create the best environment for introduction of the larvae. There are two common methods of applying the maggots to a wound. In the contained method, the larvae are in a "biobag" between layers of sealed dressing. The maggots feed through the dressing and their secretions reach the wound through the dressing. In free range application the maggots are placed directly in the wound, and then a dressing "cage" is applied around the wound to prevent escape. Air must be able to penetrate the dressing to assure survival of the larvae. When comparing the two methods, significantly better outcomes and lower numbers of maggot applications were needed with the free range group (7).
The maggots are applied to the wound, using approximately 10 maggots per square centimeter of area (2). The patient must be compliant in observing non-weight-bearing status of the affected area and in avoiding exposure of the area to excess heat or water. If there is significant drainage the patient may need to change the outer dressing after 24 hours. Return visits every 2-3 days for the duration of treatment are necessary for dressing and maggot removal and application of new larvae. The maggots are physically removed from the wound and discarded with the facility's infectious waste. Contraindications for MDT include egg, soybean, fly larvae, yeast or adhesive allergies, lack of wound hemostasis, deep tracking wounds, osteomyelitis or serious infections, coaggulopathies, hypersensitivity to movement and psychological issues (3). Although many subjects treated with MDT experienced adverse social reactions and increased odor from the wound during MDT they would still agree to MDT again if the situation arose, and would recommend this modality to others (8). Some patients find increased pain in the wound area during MDT, but in 78% the pain can be managed analgesically (9).
Maggot application utilizes various mechanisms of wound healing to achieve satisfactory results. A maggot develops very quickly in the 16-40 hours after hatching and can consume 20- 25mg of food during this time. Therefore, 400-600 maggots 16 hours old could consume 10-15g of necrotic tissue in a 24 hour period (1). Since the lavae feed on only necrotic or partially decomposed tissue, they are able to debride a wound effectively without damaging healthy tissue. This action is accomplished as the larvae anchor to the substrate with their mouth hooks. This physical action tears the necrotic tissue and allows the maggot's digestive enzymes to penetrate the necrotic tissue. The secreted material "pre-digests" the tissue and then is ingested along with bacteria that may be present in the wound. This leads to wound disinfection during MDT. The bacteria ingested pass through the lavae's digestive tract and is destroyed in the mid- and hindgut sections of the tract (1). These antibacterial excretions are shown to be effective even on MRSA and E. coli. The excretions of the maggots contain chemicals that have been shown to stimulation granulation and change the pH of the wound to also provide a better environment for granulation. The motion of the larvae in the wound is theorized to aid in granulation by mechanical stimulation of the remaining healthy tissue. It has also been shown that MDT improves tissue oxygenation and decreases wound-related edema by improvement of blood circulation (1).
Future studies in this arena may compare MDT versus surgical debridement, allow MDT to become a treatment of choice instead of last resort, and especially to isolate and identify the maggot-derived factors conducive to healing. These advances would lead to being able to provide the benefits of associated with MDT – without maggots. Maggot Debridement Therapy is becoming more widely practiced and accepted and it is useful for the O&P caregiver to have a basic knowledge of this treatment modality. As the practice spreads, clients may receive orthotic or prosthetic care before, during or after MDT and a general understanding of this treatment will be imperative for the practitioner to provide the best possible level of care.
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Claxton MJ et al. 5 questions – and answers – about maggot debridement therapy. Adv in Skin & Wound Care. Mar/Apr 2003: 99-102.
Sherman, RA. Maggot therapy for treating diabetic foot ulcers unresponsive to conventional therapy. Diabetes Care 2003 36(2): 446-451.
Armstrong DG, Salas P, Short B, Martin BR, Kimbriel HR, Nixon BP, Boulton AJ. Maggot therapy in "lower extremity hospice" wound care. J Am Podiatric Med Assn. May/Jun 2005: 95(3): 254-257.
Sherman, RA. Maggot versus conservative debridement therapy for the treatment of pressure ulcers. Wound Repair Regen 2002 10: 208-214.
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Steenvoorde P, Buddingh T, Oskam J. Determining pain levels in patients treated with maggot debridement therapy. J Wound Care 2005 Nov: 14(10): 485-488.