The role of maggots in wound healing

A problem presented at the UK MMSG Nottingham 2001.

Presented by:
Prof Dave Pritchard (Pharmaceutical Sciences, University of Nottingham)
S Franks, A Koerber, D Pritchard, J Ward

Problem Description

Chronic or intransigent wounds are wounds which, left to themselves, do not heal, nor do they respond well to clinical treatment. Venous ulcers, diabetic ulcers and pressure sores are the most common occurring chronic wounds and they all share an underlying physiological condition which promotes chronicity: a reduced blood flow to the wound site.

The wounds are localised areas of damaged tissue which are bordered by living cells. The wounds tend to range in size from about 5–40 cm2. Importantly, the damaged tissue is typically infected by bacteria which makes the wound more difficult to treat. The bacteria in the chronic wound exist in biofilms rather than the planktonic state (planktonic bacteria being flushed by the wound exudate and more easily dealt with by the immune response), which makes them harder to remove. They prevent wound healing through the release of toxins and add to the health risks of the patient.

Larval (maggot) therapy would appear to initiate the resumption of wound healing. Data exists on the types of larval secretion (a mixture of proteolytic enzymes) which could aid this process and their modes of interaction with host tissue and microbial flora. Models are required to help interpret and quantify the interactions between the larvae, their secretions and the wound healing process. For further background see Sherman RA, Hall MJR & Thomas S (2000) Medicinal maggots: An ancient remedy for some contemporary afflictions. Ann. Rev. Entomol 45, 55-81.

Study Group Report

Mathematical models were developed to describe the effect of maggot therapy upon chronic wounds. We have focused our modelling on the presence of bacteria in the wound; their inhibitory effect on wound healing and the importance of the bactericidal effect of maggots. Both of the models presented clearly demonstrate that an application of maggots can shift a wound from a chronic state to a healing state.

The results qualitative rather than quantitative, and more experimental data is required to estimate parameters and check the simulations. However, before, or at the same time as, these parameters are sought, the mathematical models require further refinement to include more detail of the biology. For example we could explicitly include the degradative effect of maggot secretions upon fibrin and the resulting increased blood flow to the wound site, as well as the stimulatory effect of fibrin fragments on the body's tissue repair mechanisms.

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