Maggot Therapy

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Chapter: Pharmaceutical Microbiology : Alternative Strategies For Antimicrobial Therapy

Chronic infected wounds arising from conditions such as diabetes mellitus and peripheral vascular disease are a major problem, and their incidence is increasing.


MAGGOT THERAPY

 

Chronic infected wounds arising from conditions such as diabetes mellitus and peripheral vascular disease are a major problem, and their incidence is increasing. Whereas normal wounds go through well-defined phases of healing, chronic wounds do not heal because of the presence of necrotic tissue, slough, debris and infection. In order to allow the wound to begin to heal it is necessary to physically remove the necrotic burden, in a process known as debridement, and also deal with the infection. Clearing the wound of necrotic and devitalized tissue is normally carried out surgically before application of antimicrobial agents to remove the infecting pathogens. The mechanical techniques used in debridement are varied and can lead to pain and damage to underlying healthy tissue.

 

The use of maggots to facilitate wound debridement and subsequent healing has been known for several centuries, but its association with modern medicine goes back approximately 70 years. However, the clinical use of maggots dwindled with the advent of antibiotics and has only now experienced a resurgence of interest. The main focus of attention has been in the area of wounds infected with MRSA. The larvae of the blow fly Lucilia sericata are grown under sterile conditions and used when they are less than 8 hours old, at which point they are only 1–2 mm in length. Up to 1000 maggots are placed in the wound, covered to prevent escape and left for 1–3 days. The maggots require a moist environment for optimal activity and their secretions contain multiple proteolytic enzymes which degrade necrotic tissue. This digested material is subsequently consumed by the maggots as a source of nutrients, but it has been suggested that there is also a mechanical component to the clearing of necrotic tissue. One of the characteristics of the larvae is that they try to avoid light and as a result of their small size they tend to burrow into deep crevices which may have proved difficult to debride mechanically. The larval secretions contain ammonia which increases the local pH producing an antimicrobial effect, and in addition the maggots ingest the bacteria, thus clearing the site of infection. The presence of the maggots also leads to stimulation of granulation tissue formation and hence promotes healing.

 

There is now abundant literature which appears to affirm the view that maggot therapy can play an important role in the treatment of chronic infected wounds. However, a large (267 patients) multicentre trial was carried out in the UK recently comparing maggot therapy with a standard debridement technique (hydrogel) for the treatment of chronic infected leg ulcers. The authors found that there was no difference in healing times between the two groups and the larval group experienced more pain. Nonetheless, the larvae did reduce the time to debridement. Some workers have shown that the antimicrobial efficacy of the larvae is dependent on the species of bacterium under investigation. Gram positive bacteria such as Staph. aureus are very susceptible, whereas Gram-negative bacteria such as Ps. aeruginosa are more resistant. The precise reasons for this are unclear. Additional hurdles to the widespread use of maggot therapy include patient acceptability and resistance of medical staff to apparently ‘old-fashioned’ techniques. Hence the case for maggot therapy is equivocal, and more basic research is required to understand why it appears to be effective in some circumstances and not in others.

 

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