Human Biology 153
Parasites and Pestilence
28 February 2010
Maggot Debridement Therapy: Putting Parasites to Use
Maggot debridement therapy, biosurgery, and larval therapy all refer to the intentional introduction of maggots into a wound in order to clean the wound and promote healing. Throughout the 18th, 19th, and 20th centuries, a series of wars resulted in a huge incidence of battle injuries, thus creating a demand for the successful treatment of chronic open wounds. Over the course of several centuries, the observation of the beneficial effects of maggot infestation of a wound led to using sterile maggots to clean those wounds and encourage healing. Even with all the technological progress that has occurred over the last century, maggot therapy continues to be a good treatment option for chronic wounds. One study on the treatment of pressure ulcers indicated that maggot therapy was far more effective than conventional methods of wound debridement. The study tested patients whose wounds were not healing normally and found that 80% of maggot-treated wounds had been completely debrided in 5 weeks, compared to less than half of the conventionally-treated wounds. Maggot treated wounds also were more likely to decrease in size and show an increase in healthy tissue (Sherman 210). In fact, because of the emergence of drug-resistant bacteria, maggot therapy may even be more beneficial today than in the past.
Myiasis—the infestation of fly larvae in human tissue—has been recorded as an affliction as far back as the Old Testament, and using maggots for therapeutic reasons has been around for nearly as long. Evidence suggests that several ancient cultures as widespread as the Ngemba tribe of New South Wales to the Mayans of South America used maggots to help heal wounds (Whitaker et al. 409). The beneficial effects of maggots in wounds was first noted in Western medicine by the French physician Abroise Paré in the sixteenth century. Paré noticed that after “a great number of worms came forth by the holes of the rotten bones from underneath the putrefied skull” of an injured patient he “recovered beyond all men’s expectation” (Goldstein et. al. 476). More than two hundred years later, Napolean’s surgeon, Baron D. J. Larrey noticed the phenomenon as well. While injured soldiers were disgusted to discover maggots in their wounds during a campaign in Syria, those with the maggots ultimately had better prognoses than those without.
It was during another war, the American Civil War, that a Western physician was first documented purposefully infecting wounds with maggots in order to promote healing (Whitaker et al. 409). John Forney Zacharias introduced maggots to cases of gangrene in soldiers with great success, but the treatment method did not catch on due to the growing popularity of germ theory and the natural associations between germs and maggots. Chronic wounds were still just as dangerous, however, and since there were few other treatment options, the case fatality ratio for open wounds was high throughout the First World War. After the war, a former field surgeon named William S. Baer began experimenting with sterilizing maggots before introducing them to the wounds. This sterilization process both prevented cases of tetanus and gangrene that had been known to have been cause by contaminated eggs and also improved public perception of the treatment when used in conjunction with specialized bandages that kept the maggots contained and out of view. Dr. Baer ushered in a period of popularity for the treatment, which was used in over 300 hospitals in the United States and Canada alone (Nigam et al., “Part I” 223). Then, in the mid-1940s penicillin became widely distributed and maggot therapy fell out of favor again. It was not until the last decade, in light of antibiotic resistant bacteria, that researchers began rethinking the potential benefits of maggot therapy. A series of studies revealed that maggot therapy is generally faster and less invasive than other techniques in healing chronic wounds; in the past decade, patients have used maggot therapy after other methods have failed.
Maggot debridement therapy is essentially the manipulation of a pathogenic condition, myaisis, into a state beneficial to humans. There are many species of flies that are capable to infect vertebrate hosts both as a necessity and if convenient. Obligate parasitic flies, those that require the host in order to complete their lifecycles, generally rely on the ingestion of living tissue in order to survive. Facultative parasitic flies, on the other hand, only parasitize humans if conditions are favorable, which means the presence of necrotic tissue, which mimics the parasite’s natural environment—carrion (Nigam et al., “Part I” 224). There are species of flies whose larvae will feed on both living and necrotic tissue, so it is vital to use a species that will only feed on dead tissue for maggot debridement therapy in order to avoid damage of otherwise healthy tissue. The species most commonly used is the common green-bottle blowfly, Lucilia sericata (or Phaenicia sericata). This species is unable to ingest human live tissue (although curiously it can ingest the healthy tissue of a sheep), and is also convenient for maggot therapy because of the ease with which it can be bred in the lab.
A L. sericata fly begins its life as one of two to three thousand eggs laid by the female directly onto a potential food source; necrotic tissue in chronic wounds is an ideal spot for the female to lay these eggs because the warm, moist environment prevents desiccation of the eggs and subsequent larvae. Once larvae hatch from the eggs after 18-24 hours, they will feed on the surrounding tissue for four to five days and grow to approximately 10mm in length, after which time they will leave the carrion or wound to transform into pupate and eventually adult flies (Nigam et al., “Part I” 224). During the larval stage, the maggots feed by first liquidating the dead tissue through the secretion of a number of proteolytic enzymes.
Maggots that are destined for treatment purposes begin as eggs deposited onto porcine liver by adult female green-bottle flies (Nigam et al., “Part I” 225). The eggs are then separated, chemically sterilized, and tested to “ensure their microbiological status” before being permitted to enter the larval stage and being applied directly to the wound. As mentioned previously, this sterilization process is imperative to prevent that pathogenic bacteria from being introduced into the wound along with the larvae as had occurred in the early days of maggot therapy.
The first step to maggot therapy is to place a piece of hydrocolloid dressing with a wound-sized hole around the wound. This dressing protects the surrounding skin from irritation due to maggots crawling on unbroken tissue and the proteolytic enzymes that they secrete. The maggots are then introduced to the wound and covered with nylon netting to prevent escape. Finally, a plain absorbent pad secured with tape is placed over the netting to wick away excess moisture and to keep the maggots away from view (Whitaker et al. 411). After 3-5 days the maggots are removed simply by rinsing off in the shower. The maggots should come off easily after this length of time; if any remain it is a sign that the wound is not completely debrided. Multiple applications of maggots are safe and are often necessary in more complicated wounds such as osteomyelitis (Wollina et al. 286). Maggot therapy has been found to be useful on all types of superficial wounds including various types of ulcers, osteomyelitis, necrotizing faciitis, burns, post surgical wound infections, and even gangrene, with the main exposed organs or major blood vessels in the wound (Whitaker et al. 411).
The best understood and most straightforward benefit of maggot therapy on wounds is debridement. The maggots rid the wound of dead tissue and other debris and thus enable the healing process to begin. This cleaning of the wound occurs naturally under normal immune system responses, but in chronic wounds this process often fails to occur effectively. These wounds are conventionally cleaned in a number of different ways: surgically by simply removing dead tissue using a scalpel, mechanically by irrigation or wet-to-dry dressings, or chemically using enzymes or hydrogels that promote autolysis. These techniques, however, are often incapable of simultaneously removing all necrotic tissue and avoiding harming healthy tissue. Maggots offer a more effective and less invasive alternative for wound treatment. The maggots debride the wound both mechanically and enzymatically. Feeding normally inside the wound, the maggots release four proteolytic enzymes that preferentially break down dead tissue (Nigam et al., “Part I” 225). The maggots allow deeper penetration of their enzymes as well as dislodging additional necrotic tissue and debris simply by wriggling around in the wound and grabbing on to wound tissue with their mandibles.
Maggot therapy has been found to significantly reduce risk of infection in patients in which it is used. There has been substantial research investigating the mechanism responsible for the antimicrobial properties of maggot therapy, and while the exact biology is still unknown several different properties have been suggested. First, it is likely that the movement of the maggots and their secretions result in irrigation of the wound that reduces bacterial load. The nature of these secretions is also believed to be partially responsible for killing bacterial. For instance, L. sericata maggots release ammonia as a waste product, and this ammonia raises the pH of the wound tissue enough to render it unfavorable to bacteria. The maggots also rid the wound of bacteria by consuming those bacteria and killing them during digestion. This mechanism was first suggested in the 1930s when a research team discovered that although the stomach and crop of maggots in a wound had high bacterial loads, the hindgut was sterile. (Nigam et al., “Part II” 303-304)
Maggot therapy was found to especially affect gram-positive bacteria such as Staphylococcus aureus, which is significant because S. aureus is a major cause of antibiotic-resistant infections in hospitals (Jaklic et al. 617). S. aureus became resistant to penicillin soon after its widespread release, and after a second drug, methicillin, was used to control penicillin-resistant strains, strains evolved that were also resistant to the new drug (methicillin-reistant S. aureus or MRSA). There have even been strains of the bacteria discovered that are resistant to a third drug, vancomycin (Nigam et al., “Part I” 226). Maggot therapy offers an alternative treatment option that fights these resistant bacteria without posing much of a risk of creating even stronger and more resistant bacteria.
Enhanced Healing Effects
The final benefit of maggot therapy is the enhancement in healing that it offers. Wounds in which maggots are used often heal more rapidly than others, and many researchers have suggested that this improvement of healing is due to factors extending beyond just the decrease of necrotic tissue and bacteria. It is possible that the movement of the maggots through the wound tissue increases oxygenation and enables the healing process to effectively occur. Additionally, the increase in pH caused by ammonia that was previously mentioned as a factor in reducing infection also plays a role in promoting healing by creating an environment conducive to the growth of new granulation tissue (Nigam et al., “Part II” 305). One final theory that has been researched extensively in the last several years is that there are agents within the secretions of the maggots that are themselves growth factors (Whitaker et al. 411). One study found that extracts of the secretions increase the production of fibroblasts, an essential component of normal wound healing (Nigam et al., “Part II” 305).
Maggot therapy is still considered to be a therapy that should only be employed as a last resort, but there is substantial evidence that suggests that it should be used more often. Contrary to most people’s expectations, several different studies have indicated that maggot therapy is well received and tolerated by patients; although practitioners are somewhat hesitant to suggest it or even to use it after a patient has made a request (Sherman 213, Wollina et al. 288, Nigam et al., “Part II” 306). Maggot therapy has been found to be extremely efficacious in the healing of wounds, which means that it would not only offer great benefits to the patients upon whom it is used but also to the greater healthcare system by decreasing the length of hospital stays and the frequency with which more expensive interventions are used. An increase in maggot therapy would also likely result in a decrease in antibiotic use, which would help prevent the evolution and spread of antibiotic resistant bacteria. In summary, maggot therapy has a wide range of benefits that should be carefully considered before its use is rejected simply out of disgust. There is a reason why a centuries-old cure once used on the battlefield is still being used now in an age of complex technological interventions.
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Nigam, Yamni, et. al. “Maggot Therapy: The Science and Implication for CAM Part II—Maggots Combat Infection.” eCAM 3.3 (2006):303-308.
Sherman, Ronald. “Maggot versus conservative debridement therapy for the treatment of pressure ulcers.” Wound Repair and Regeneration 10.4 (2002):208-214.
Whitaker, Iain S, et al. “Larval therapy from antiquity to the present day: mechanisms of action, clinical application and future potential.” Postgrad Med J 83 (2007): 409-413.
Wollina, Uwe, et. al. “Biosurgery in wound healing—the renaissance of maggot therapy.” JEADV 14 (2000):285-289.