Maggot Debridement Therapy: A Suitable Treatment Option for Chronic Wound Care

EMILIA M. KOOIENGA; JEROME GODDARD, PHD

Chronic, non-healing wounds due to burns, diabetes, and other injuries cost United States patients about 50 billion dollars each year. Traditionally, treatment has involved surgical debridement of necrotic tissue and frequent cleaning and changing of the wound and dressings to manage infection risk and promote healing. In the 1920s, a new method of wound debridement called maggot debridement therapy or MDT emerged and has continually developed into an effective treatment strategy. Sterile, live blow fly larvae are either placed into the wound and sealed in by gauze or held in place by a mesh bag in the wound. Secretions of the larvae kill bacteria, dissolve necrotic tissue, and stimulate healthy tissue formation. Studies have shown that MDT has the power to debride and contribute to wound healing as early as four weeks, compared to conventional therapy. With multiple benefits and few side-effects, MDT is a well-supported and increasingly accessible tool for physicians in chronic-wound treatments.

Chronic wounds affect about 2% of the population of the United States, with a total cost of about 50 billion dollars annually. 1 The cost of care increases in those patients with co-morbidities, complications, or other conditions related to their wounds. Traditional therapies for chronic wound care consist of surgical debridement of necrotic tissues supplemented by antibiotics. Maggot Debridement Therapy (MDT) is an alternative method of debridement in wound care that warrants further exploration. The use of maggots in wound care was first noted by William Baer at Johns Hopkins hospital in the 1920s as having a positive impact on healing soldiers’ wounds; 2 however, post-World War II, maggot therapies were mostly replaced with antibiotic therapy and surgical techniques. 2 In this paper, we explore traditional therapies used in debriding wounds and compare them with the merits, uses, and efficacy of MDT.

The infestation of living vertebrates with dipterous larvae is called myiasis and can be either facultative (opportunistic) or obligate. Obligate myiasis constitutes true parasitism and is a complex issue. The subject of this paper is facultative myiasis and how it can be used in clinical medicine. Flies, particularly those in the family Calliphoridae, lay eggs on dead animals that the developing larvae consume. Unfortunately, sometimes the adult flies mix up what is dead or alive and may lay their eggs in malodorous, pus-filled wounds on people and animals. This is sometimes termed cutaneous myiasis where fly larvae enter an open wound, feeding upon dead tissue in the wound. They do not subsequently enter into living tissue. While there are stories of people stranded outdoors after an accident with maggots in their lesions (supposedly helping prevent infection), these infestations may lead to secondary infection of the wound. 3 “Wild” or naturally occurring flies and their larvae may transport a host of pathogens into the wound. For example, Staphylococcus aureus and other Group B Streptococcus organisms have been isolated from myiasis patients’ wounds. 3

Chronic wound care typically refers to those slow- or non-healing ulcer-like sores most often found on bedridden patients or diabetics. 4 Pressure ulcers are common among bedridden patients in long-term inpatient care or who are afflicted with medical conditions that limit or prevent movement of the body. 5 These ulcers develop on the less padded areas of the body with more delicate skin and less fat. In comatose patients, for example, ulcers are commonly found on the back, hips, heels and ankles. 5 Patients who rely on the daily use of a wheelchair often find developing ulcers on their shoulder blades, tailbone, and back from both pressure and friction. Diabetic patients, as well as other patients with vascular diseases, are also at risk of developing pressure non-healing ulcer wounds. Decreased blood flow and nerve damage from diabetes complications mean the area, once pressure is applied, gets even less blood. This leads to tissue death as nutrition and hydration are withheld from the area. Nerve damage in the ulcer-forming area means that the patient may not feel the excess pressure or friction and will not be aware of the need to change body position to prevent injury. Complicating matters, secondary infections often occur in persistent open wounds. Methicillin-resistant Staphylococcus aureus (MRSA), in particular, is a notable concern for those with chronic wounds.

Traditional therapies for chronic wounds include frequent dressing changes and debridement to remove and manage the amount of necrotic tissues accumulating in the wound. Debridement removes these dead and decaying tissues to facilitate the growth of new healthy tissue. Not all wounds respond well to debridement, so it is up to the discretion of the physician if this is an appropriate treatment plan. Dangers of not debriding a chronic wound include increased susceptibility to infection and inhibition of healthy tissues. 6 Typically, the body is well equipped to slough off its own dead skin cells, but in instances where the area is large or particularly deep, sloughed-off tissue may not leave the wound. In such cases, intervention is required. There are two types of debridement therapies: autolytic and active. In autolytic debridement, hydrocolloids and gels increase the moisture level in the lesion, helping to both keep the wound clean and stimulate the body to degrade these tissues. Active debridement involves manual removal of tissues. In that case, surgeons precisely remove necrotized tissue with scalpel and forceps or with scissors. 6 However, this often leaves an irritated and bleeding wound bed.

Despite having the potential to cause harm to humans, fly larvae, or in this case maggots, do have a beneficial use. When raised on a diet of sterile media and properly handled, they are capable of debriding a wound without spreading infection or feeding on living tissues. The most commonly used larvae for MDT are Lucilia sericata, which are blow flies in the family Calliphoridae (Figure). 7,8 These sterile, live, medical-grade “biosurgeon” maggots can be applied using a special “maggot cage” dressing that confines the maggots to the wound site and prevents escape. These maggots have been reared in pure culture for more than twenty-two years and are able to dissolve necrotic tissue and bacterial biofilms. 9 Their excretions kill bacteria, dissolve old tissue, and stimulate generation of granulation tissue – a type of new, healthy tissue that forms in healing wounds. 10 Once maggots have been applied (the dosing range for maggots per square centimeter varies from 4-10 maggots depending on the healthcare provider and species/stage maggots being used). Once they are sealed against the wound with dressings, they must be checked on every two to four hours to ensure that the outer dressing is dry, the seal is strong, and that there are no openings from which maggots can escape. The maggots can be left in the wound until the area is debrided. Once the necrotic tissue has all been dissolved and ingested, maggots will cease feeding and will leave healthy tissues alone. MDT has the potential to reduce amputation rates, speed up healing using fewer treatments, and is highly selective. Maggots will not feed on non-necrotic, living tissue and generally cause no harm the patient being treated. MDT has even been shown to remove MRSA (Methicillin-resistant Staphylococcus aureus), a topic of much current interest in the medical world. After treatment is completed, the maggots can be disposed of with normal medical waste after flushing the wound thoroughly with sterile fluid to remove any residual maggots or excretions. Besides chronic wounds, MDT can be used for patients with other difficult-to-heal malignant wounds, venous wounds, and burns. 9 It may also be prescribed for patients whose condition is not stable enough to undergo surgical debridement. Patients with rapidly advancing infections or deteriorating condition should not undergo MDT. MDT can take anywhere from four days to several weeks to completely debride a wound, depending on the extent of the injury. Wounds must be open to the outside of the body, not completely dry, not near major blood vessels, and cannot include bone or tendons.

MDT has been successfully studied in a case study of 18 male, diabetic veteran patients with a total of 20 non-healing wounds. 4 Six were given conventional surgical and chemical debridement treatment, 6 given only MDT, and the remaining 6 given conventional therapy followed by MDT. The first two weeks of conventional therapy saw no significant debridement, whereas there was a marked decrease in necrotic tissue in those patients receiving MDT. Five weeks from the start of treatment, conventional treatment still saw 33% of the wound covered in necrotic tissue. At four weeks, MDT had completely debrided all wounds, increased healing rate, and encouraged the growth of the healing-indicative granulation tissue. 4

Another study was conducted assessing excretions of the blow fly larvae reared for MDT. Researchers saw antiseptic activity in the wound bed of patients treated with MDT and investigated potential for these secretions to inhibit growth of Staphylococcus aureus in nonhealing wounds. Secretions from maggots were collected and tested with S. aureus both alone and with supportive ciprofloxacin antibiotic. Secretions alone showed inhibition in bacterial growth, and when in conjunction with ciprofloxacin, resulted in up to 50% reduction in S. aureus colonization. 4

While MDT’s effectiveness in wound debridement and wound healing is indisputable, is it still worth the time and effort involved? Traditional surgical methods involve prep work, anesthesia, surgery time, and recovery as well as careful tending to the wound as it heals because, as previously mentioned, surgical debridement results in a raw and bleeding wound bed. Recall that MDT is usually administered by a physician carefully placing the recommended dosage of maggots in the wound, followed by extensive dressings designed to protect the maggots and keep the patient safe. It requires monitoring every two to four hours to ensure the wound and dressing are properly aligned, as one study showed that 43% of the time, maggots have escaped. 11 A new method for administering MDT has recently been reported. 11 The BioBag ® is a small mesh polyester bag with varying numbers of maggots and mesh sizes. The intention is to reduce time of setting up the wound with specialized dressings. In predetermined dosages, a BioBag ® can be ordered on an as-needed basis for chronic wound patients. The BioBag ® is placed in the wound for four days and covered with simple gauze dressing to hold it in place. The mesh allows the proteolytic enzymes, anti-microbial, anti-inflammatory, and cell-stimulating secretions to enter the wound, turning necrotic tissue into a semi-liquid that the maggots are then able to consume. A research study showed no difference in effectiveness between the BioBag ® and other MDT administration techniques. 11 With this newfound method of administering MDT, there is less time spent changing dressings and monitoring maggot activity. Additionally, wound care can be performed by a caregiver or family member at a patient’s home upon being given instruction on sterile techniques and how to change the dressing. MDT is now faster to administer, faster to heal and debride wounds, continually getting easier to use, and puts less strain on the patient’s body than conventional therapies. A cost analysis study of MDT versus traditional debridement showed that, on average, MDT costs about 50% of conventional therapy; it reduces pain perception in patients and increases healing rate. 12

MDT therapy has multiple benefits, few side-effects, and is an increasingly accessible tool for physicians to use in treating non-healing chronic wounds. Its low cost and relative ease of use make it a more accessible treatment to patients, while its selective, precise, and gentle debridement leaves the wound clean but not bleeding. MDT is well-supported as a suitable treatment option for non-healing chronic wounds.

Acknowledgment: The authors have no conflicts of interest to disclose.

Author Information: Department of Biological Sciences, Mississippi State University (Kooienga). Department of Biochemistry, Molecular Biology, Entomology, and Plant Pathology (Goddard).

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