Larval Therapy for the treatment of diabetic foot ulcers

Larval Therapy: an alternative treatment of the chronic infected diabetic foot ulcer.

Due to rising costs and increased resistance to anti-biotics larval or maggot therapy is once again gaining popularity (Twedell, 2009). The benefits of intentionally treating wounds with maggots were investigated after World War I (Baer, 1931). It was noted during that war, that wounds accidentally infested with maggots seemed to be debrided of necrotic tissue, showed healthy granulation tissue and were colonised by fewer microbes than other wounds (Baer, 1931). The case selected for this paper involved a male patient, 64 years of age with diabetes mellitus (Type II) who had undergone an amputation of the second digit of the left foot a year ago after a neuroishcaemic ulcer on the apex of the toe had become necrotic. The wound at the site of the amputation had failed to heal and was prone to intermittent S.aureus infections which were proving difficult to eradicate with oral antibiotics. The patient’s drug history and past medical history were un-remarkable for a diabetic patient only highlighting a history of previous foot ulceration. The aim of this paper is to explore the evidence within the literature along with limited observations of the patient who underwent larval therapy, in order to gauge the efficacy of this intervention in the treatment of the chronic diabetic foot ulcer.

Bonn (2000) suggests that larval therapy is a reliable intervention for wound management as the technique was found to be easily learned and replicated by practitioners working both in primary and secondary care scenarios. Before the larvae are applied to a wound a few factors need to be considered. Larvae need a moist environment in which to survive (Drisdelle, 2003) and when used in plantar foot ulcers care must be taken to ensure larvae are not crushed underfoot (Mumcuoglu et al.,1998). Larvae can remain in place for up to three days (Twedell, 2009) and are easily removed by flushing away with saline solution and disposing of as clinical waste (Mumcuoglu et al., 1998). The patient in question being treated had the larvae replaced at two day intervals. Another factor to consider is that termed the “Yuk” factor within the literature. Social factors such as the odour associated with larval therapy and a feeling that larvae are considered “eerie” amongst patients were regarded as deterents to undergo treatment. Steenvoorde et al. (2005) found these perceptions to be untrue and that patients were quite willing to try larval therapy as long as information was given about it. Collier (2009) suggests that it is in fact the health professionals and not the patients that possess the “Yuk” factor.

Larval therapy is thought to have a theoretically positive effect on healing. Excretion of ammonia and calcium carbonate by larvae changes an acidic wound pH to a beneficial alkaline pH. Mechanical stimulation and excretion of growth-stimulating factors by larvae also encourage the formation of granulation tissue (Mumcuoglu et al., 1998). Consensus within the literature as to whether wounds heal quicker using larval therapy over conventional methods, though, has not been reached. Sherman (2003) reported hastened healing rates of wounds in a diminutive population of eighteen patients. This author is sceptical of Sherman’s study due to the fact that Sherman is the owner of the facility that is the sole supplier of medicinal larvae in the U.S.A. A randomised trial involving 267 patients published a more plausible result finding no difference in the healing rates of wounds treated with larvae (Dumville et al., 2009). Within the literature, the assessment of larval therapy is commonly based on the primary outcome measure of healing/wound closure. The patient being

observed therefore had his wound measured to indicate the size of the wound before the commencement of larval therapy.

Another factor in larval therapy involves the larvae secreting proteolytic enzymes that break down necrotic tissue and liquefy it for ingestion thus debriding the wound (Drisdelle, 2003). Not all species of larvae are suitable for medical use as some attack healthy human tissue. This is not the case with the common greenbottle or Lucilia sericata (Bonn, 2000). Only two randomised trials on the efficacy of larval therapy could be located in the literature. These trials agreed that larval therapy was more effective at wound debridement than the conventional hydrogel-dressing intervention (Walker, 2000; Dumville et al., 2009). Secondary outcome measures, within the literature, often include time to debridement. The patient being observed, therefore, had photographs taken of his wound for later comparison for the presence of necrotic tissue and slough.

As they feed, the larvae ingest bacteria which are lysed during digestion (Drisdelle, 2003). Certain secretions/excretions by the larvae, which have not been identified, are believed to have anti-bacterial qualities. These have been shown to be effective against microbes such as S.aureus (including Methicillin-Resistant S.aureus [MRSA]), E.coli, E.cloacae and P.aeruginosa (Bowling et al., 2008). Andersen et al. (2010) argue in their study, to the contrary, that P.aeruginosa is a major threat to the survival of larvae within a wound. Bowling et al. (2007) showed the capability of larval therapy to eradicate MRSA from wounds but Dumville et al (2009) countered by showing little effect against MRSA in their randomised trial which admittedly might have been underpowered. The patient being observed had confirmation of a S.aureus infection within his wound, through analyses of a swab taken, before larval therapy commenced. The photographs taken also showed signs of inflammation.

After a very short follow-up period of one week after the patient started larval therapy, his wound was once again measured and its appearance was compared with that of the photograph taken prior to treatment. There was little or no difference in the wound’s size but the wound did appear to be markedly debrided of necrotic tissue, was less sloughy and seemed to show an increase in granulation tissue. A swab to compare the difference in microbe colonisation was unfortunately not taken on the day of the author’s follow-up of the patient. There did seem to be a slight dampening of inflammatory signs noted prior to treatment though. Though the assessment of the wound is open to subjectivity, as it seems to be in most of the studies read, this author believes that both the literature and the case-based study conclusively suggest an increased rate to debridement over conventional interventions. Larger randomised controlled trials are needed in the future to better assess the efficacy of larval therapy in wound healing and infection eradication as much of the literature seems to be contradictory as has been highlighted above. On balance, larval therapy seems to be a cost effective alternative to other popular wound management interventions in this day and age of anti-biotic resistant microbes.

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