Biological dressings – larval therapy

Larvae of the green bottle fly can evoke feelings of disgust, but they have been used in wound healing for a long time.
They were forgotten when antibiotics and surgical wound cleansing began to be widely used, but reappeared in the spotlight in the ‘90s, when American scientists once more appreciated the extraordinary possibilities of these voracious creatures, and especially their insatiable hunger for bacteria. Larvae of the green bottle fly feed on dead tissue and harmful microorganisms residing on wounds, and thus contribute to healing.

Larvae cleanse the wound more precisely than any surgeon.

Typically, the therapy lasts only two or three days, however, we have seen cases of five-, six- and – a record holder – eight-day treatment. Larvae can be administered repeatedly, depending on healing progress.
At AZ MED Pain and Wound Treatment Centre, we have healed wounds in many patients using this method.

 

What does a dressing look like with larvae

Sterile larva cultures are grown in accordance with medical standards. They are wrapped in mesh coatings and applied directly to the wound. Carefully selected mesh weave prevents the larvae from leaving the dressing. The patient has no visual or sensory contact with the larvae.

Larval therapy is painless

In some cases, it is necessary to apply larvae directly to the wound, without a mesh. To avoid irritation, the skin around the wound is protected with zinc ointment, which prevents the larvae from leaving the wound.

Dressings are applied by a wound management specialist

The dressing is placed in the wound bed for 24-72 hours. During this time the wound is debrided, all necrotic cells and microorganisms are removed, and the regeneration process begins. Wounds with extensive necrosis require multiple applications of dressings. The therapy must be continued until a complete debridement is reached. This process can be supported with a surgical debridement. Biological material in a dressing must be alive. Thus, it is very important to protect dressings from organic fluids (the larvae will die without air), physical pressure and high temperature. If these occur, the risk of failure and the necessity of the repetition of the whole procedure must be taken into account. Studies on the effectiveness of the larval therapy show that the average healing time of 50% of wounds does not exceed 4 weeks. In case of conventional surgical methods, the same process may last up to 30 weeks and usually it does not finish with a complete closing of the wound.

More about dressings

For the healing process to begin, 4 important conditions must be met. They are referred to as TIME:

T – Tissue. The wound must be completely debrided of any dead tissue,
I – Infection. The wound must be free of infection,
M – Moisture. Proper moisture and liquid balance in the wound must be maintained
E – Edge. The wound edge must be healthy as its cells are necessary for further division in the wound bed.

In order to prepare the wound all the above-mentioned conditions must be met, what requires great coordination of many medical professionals and various actions, which can efficiently determine the successful termination of particular processes.

Biological dressings and TIME

Larvae caged in a dressing influence simultaneously all the processes in the TIME procedure, what makes this method highly effective, fast and safe for the patient.

T – Living organisms mechanically remove dead tissue from the wound bed and support the healing process with hydrolytic enzymes (mainly proteolytic, glycolytic, lipolytic and endonucleases). The enzymes are highly selective in the wound debridement process, because they “dissolve” only dead tissue and leave healthy tissue unaltered. The mechanism of selective debridement is very simple: serine protease, which is secreted in high concentration, is inhibited by proteins present in blood. At the border between living and dead tissue, at the site of vascularisation, the enzymes activity is inhibited.

I – Larvae of green bottle fly, L. sericata, secrete and release antimicrobial peptides (AMP) into the wound bed. The peptides efficiently fight microorganisms such as Gram-positive bacteria (lucifensin, seraticin, MAMP), Gram-negative bacteria (proline dimer, hydroxybenzoic acid), and fungi (lucimycin peptide). The production and synthesis of these substances depends on the type of microorganisms present in the wound. Moreover, as early as after the first 42 hours of the therapy, it can be easily noticed, that unidentified substances contained in larval secretion efficiently reduce inflammation in the wound, inhibiting the production of proinflammatory cytokines and promoting the production of anti-inflammatory cytokines by phagocytes.

M – Larval secretion inhibits the production of hydrogen peroxide and elastase enzyme by neutrophils. Both substances destroy living cells in the wound bed, what is of great importance especially in chronic wounds. The environment in the wound is also changed due to the action of hydrolytic enzymes and proteins targeted at microorganisms. Such action allows for a successful removal of bacterial-fungal biofilm.

E – Serine proteases from larval secretion efficiently influence the fibroblasts migration in the wound. This is the key factor contributing to the initiation of the healing process. Cell growth factors (basic fibroblast growth factor, endothelial cell growth factor) influence the rapid division of fibroblasts, keratinocytes, and cells which build blood vessels. As a result, the wound bed quickly fills with granulation tissue cells, and tiny blood vessels start to appear. Both events guarantee a fast healing process.

 

Mechanism of action and effectiveness

It has been believed that the main task of the larvae is to clean wounds from dead tissue mechanically with the assistance of hydrolytic enzymes secreted externally during the exploration of the wound bed. The larvae have been known for their beneficial antibacterial effects, mainly damaging biofilm in the wound. The stimulation of healing and tissue regeneration has been also observed. Nevertheless, in the 21st century, intensive scientific research identified at least 70 active substances secreted by the larvae in the wound bed, what allowed for multifaceted wound management.

 

Watch how larvae of the green bottle fly heal wounds

Watch a fragment of 36.6 on TVN, where we discuss treatment with biological dressing.

Literature data on the effectiveness of larval therapy indicate that in 50% of cases the average healing time of non-healing wounds does not exceed 4 weeks, whereas traditional surgical methods can take even 30 weeks and usually do not end with a complete healing of the wound.

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