Larval therapy

Case history

A woman aged 82 years was referred to hospital by her general practitioner with a non-healing foot ulcer. The ulcer had been present for over 18 months and had been treated unsuccessfully by district nurses for the past 12 months. In the past three months it had become increasing painful, interfering with walking. Doppler studies had confirmed that it was a venous ulcer. Unfortunately the patient had been unable to tolerate four layer compression bandaging. When the patient was admitted the ulcer was covered by a mixture of thick, black, dead tissue and infected yellow green slough. Initial treatment with Intrasite gel (hydrogel) was unsuccessful. She was treated with sterile larvae applied to the foot ulcer for three days (figure 1). After removal of the larvae the foot ulcer continued to improve and was healed within three weeks.

Questions

(1) Which fly is most commonly used for larval therapy?

(2) Give two ways in which larval therapy is effective?

(3) What is the main side effect of larval therapy that patients may complain of?

Answers

(1) The fly most commonly used for larval therapy is Lucilia sericata.

(2) Larval therapy is effective in that it:

• Promotes rapid cleaning of necrotic and wounds with lots of slough, of all kinds

• Controls production of offensive wound odour produced by proteolytic bacteria

• Prevents or controls infection.

Discussion

The beneficial effects of larvae (maggots) on the healing of infected wounds have been recognised for hundreds of years. It was noted that when larvae found their way into wounds by accident on the battlefield, the wounds tended to heal more quickly and with fewer complications than comparable wounds that had not become infested.

The larvae are effective in several ways. They combat wound infection by ingesting micro-organisms, which are then destroyed in their gut. In addition, they secrete chemicals, such as allantoin, with broad spectrum antibacterial activity, which contributes to wound infection control. They dissolve and devour rotting tissue and promote healing. They also evade the immune response and thus cause no inflammation. Larval therapy may stimulate the production of granulation tissue. Preliminary studies suggest that larvae are able to eradicate antibiotic resistant bacteria such as methicillin resistant staphylococcus aureus (MRSA) from infected wounds.

The fly most commonly used for larval therapy is Lucilia sericata, which is also responsible for a condition known as "blow fly strike" in sheep. The adults are an attractive metallic coppery green, hence their name "greenbottles."

In the United Kingdom sterile larvae for use in "biosurgery" are obtained from the Surgical Materials Testing Laboratory in Bridgend, South Wales.

The wound is traced out on a sterile plastic sheet, which is then cut out and transferred onto a hydrocolloid dressing. The shape of the wound is cut from the hydrocolloid dressing and discarded, and then the hydrocolloid dressing with the wound sized hole is applied to the patient. The young larvae are introduced to the wound. A piece of nylon mesh larger than the wound but smaller than the hydrocolloid dressing is then stuck down on the hydrocolloid with adhesive tape. An absorbent pad is applied to the outer surface to absorb any exudates or liquefied tissue. The dressing protects the intact skin from the potent proteolytic enzymes produced by the larvae. The larvae are usually removed from the wound after three days but may be left longer in some cases. Once the net is removed most of the larvae will fall out, or leave the wound considerably increased in size.

There are no significant adverse events linked with the clinical use of sterile larvae. An allergic reaction to larvae is a potential risk, but no such effect has so far been reported. The larvae will not burrow under the skin or attack healthy tissue. When mature, larvae must leave the wound to pupate. Consequently, when fully grown, larvae will come to the wound surface where they are readily removed. The main disadvantage of larval therapy seems to be a tickling sensation. This can, however, be dealt with by an appropriate dressing system.

Larval therapy has many advantages and should be considered in the management of problem wounds that do not respond to more conventional treatments.

Rosemary Morgan, consultant geriatrician, Mersey Hospital, Merseyside


studentBMJ 2002;10:259-302 August ISSN 0966-6494