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Larva therapy

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VOL: 97, ISSUE: 16, PAGE NO: 38

Molly Courtenay, PhD, MSc, Cert Ed, RNT, RGN, is senior lecturer, Buckinghamshire Chiltern University College, Chalfont St Giles

Modern interactive dressings sometimes take longer than anticipated to remove necrotic and infected tissue from a wound bed and surgery is not always an appropriate option. In addition, antibiotic-resistant bacteria can further complicate the management of an infected wound. The use of maggots, also referred to as larva therapy (LT), is an alternative method of management that is gaining in popularity (Courtenay et al, 2000).

Modern interactive dressings sometimes take longer than anticipated to remove necrotic and infected tissue from a wound bed and surgery is not always an appropriate option. In addition, antibiotic-resistant bacteria can further complicate the management of an infected wound. The use of maggots, also referred to as larva therapy (LT), is an alternative method of management that is gaining in popularity (Courtenay et al, 2000).

During the 1920s and 1930s, LT was a popular treatment which was used successfully to manage a variety of chronic and infected wounds (Baer, 1931; Ferguson and McLaughlin, 1935; Livingstone, 1936; Horn et al, 1976). However, with the introduction of antibiotics in the 1940s, the use of LT virtually ceased. During recent years, LT has been re-established in the clinical management of wounds and numerous papers describe the use of this technique (Courtenay et al, 2000; Courtenay et al, 1999; Walters, 1998; Evans, 1997; Thomas et al, 1996; Boon et al, 1996; Morgan, 1995).

The greenbottle blowfly
LT uses the larvae of the greenbottle blowfly (Lucilia sericata). They are produced in specialist centres in the UK, Germany, Israel, the Ukraine and Hungary (Thomas and Jones, 2000). The eggs of the adult greenbottle blowfly hatch within 12-24 hours and the larvae secrete proteolytic enzymes which, when placed in wounds, cause the dead tissue to break down into a semi-liquid form. This liquid is then sucked up and digested.

Application and removal
When introduced into the wound, the larvae are about 2mm long. No more than 10 larvae per cm2 is recommended (Thomas et al, 1996). Components of the LT dressing usually include a hydrocolloid sheet, which acts as a base and protects the skin from the enzymes produced by the larvae, a sterile piece of fine nylon mesh to cover the larvae and an absorbent pad to absorb exudate.

The larvae should be removed from the wound after three days and destroyed by incineration. They fall out of the wound once the mesh has been removed. Any remaining larvae can be removed gently with forceps, a gloved hand or irrigation with a jet of saline. Further larvae, or an alternative wound dressing, may then be applied, depending on the stage of healing.

Mechanism of action
Larvae promote healing by a number of different mechanisms:

- The irritant effects of the larvae cause the wound to produce an exudate, which washes the wound (Thomas et al, 1996);

- The wriggling larvae stimulate the development of granulation tissue (Thomas et al, 1996);

- Proteolytic enzymes secreted by the larvae digest necrotic tissue and destroy bacteria (Vistnes et al, 1981; Thomas et al, 1996);

- The larvae secrete antibacterial agents and agents that promote healing (Pavillard and Wright, 1957; Thomas et al, 1996).

The current status of LT in the UK
Although used primarily in the treatment of leg ulcers, LT is also used in hospitals and the community to treat a variety of wounds. These include pressure ulcers, amputation sites, primary burns and fungating tumours. LT rapidly debrides wounds, reducing wound exudate, odour, pain and infection, and stimulates the development of granulation tissue. It has few adverse effects and, apart from a mild tickling sensation, patients experience little discomfort (Courtenay, 1999). LT can reduce hospital stay, prevent surgery and hospital admission, and reduce the need for antibiotics (Courtenay et al, 2000).

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