Laval or Maggot therapy is used to remove the thick sloughy material that collects on a venous ulcer.
Saline is added to the pot of maggots and placed on a straining cloth
The maggots are placed on the wound supported by a surrounding bridge.
|Laval therapy and Wound Management|
By Frances Dear (Medical Student)
Chronic wounds represent a serious challenge for today’s NHS. Larval therapy involves the use of fly larvae (maggots) to heal wounds and combat infection. This practice may, at first, sound unlikely but it is effective and its use been known of for centuries.
The term “biosurgery” describes the use of living maggots on wounds to remove devitalised tissue, decrease infection and improve wound healing (Wollina et al2000), whilst leaving the healthy surrounding tissue alone. This is principally used to debride wounds such as leg ulcers, pressure sores and other lesions which contain large amounts of necrotic or infected tissue, including those with methicillin resistant Staphylococcus aureus (MRSA). Larval therapy has also been used to successfully treat burns, osteomyelitis, mastoiditis and the management of squamous cell carcinomas.
Many cultures around the world, such as the Mayan Indians and the Australian aborigines, have used the deliberate introduction of maggots into gangrenous and infected wounds. Prior to the introduction of penicillin and sulphonamides, larval therapy was used to debride wounds and improve patient prognosis.
The first medical studies of the use of maggots were documented by Dr William Baer, a US surgeon who had observed first hand the effects of maggot infestation on soldiers’ wounds in France during World War I. During the 1920’s and 1930’s, Baer successfully treated osteomyelitis and leg ulcers with maggots and reported that the therapy debrided necrotic wounds and promoted the formation of granulation tissue. Many doctors of the time used maggots to treat chronically infected and necrotic wounds. However, larval therapy fell out of favour with the introduction of antibiotics and new surgical techniques. Nevertheless, the emergence of antibiotic resistance has, once again, given birth to the renaissance of maggot therapy.
As an interesting side note, maggot infestation also plays an occasional role in solving crimes, particularly that of homicide. In a branch of science known as forensic entomology, pathologists in the US use the age of maggots found within a victim’s body to help determine the time of death.
Cost Effectiveness of Larval Therapy
The treatment of necrotic ulcers involves considerable time and expense, particularly since the current standard treatment involves the application of hydrogels. In studies, Wayman et al (2000) compared larval debridement therapy with conventional hydrogel dressings in the treatment of necrotic venous ulcers. Twelve patients were randomised to receive either larval therapy or conventional therapy. All six patients treated with larval therapy had their ulcers successfully debrided with a single three-day application. On the other hand, two of the six conventionally-treated patients still needed dressings after a month has passed. The median cost of treatment of the larval group was £78 compared with £136 for that of the conventional group.
The advantages of larval therapy therefore include decreased cost, reduced hospitalisation time, rapid debridement of necrotic tissue and infection control.
Despite this, large-scale trials of maggot therapy have yet to be carried out and are hampered by a lack of funding.
Application of Larval Dressings
Larval therapy is often used when conventional therapy has failed. Maggot infestation in vertebrates is termed ‘myiasis’. Naturally occurring myiasis can be either beneficial or harmful, depending upon the species of maggot involved. It is important to note that only certain species of maggot are suitable for medical use as some species will also attack viable tissue. The larvae of the common greenbottle fly Lucilia (Phaenicia) sericata is often used because it will only feed on necrotic tissue. In the UK, sterile maggots are bred at the Biosurgical Research Unit, Princess of Wales Hospital at Bridgend in Glamorgan, by allowing flies to lay eggs on strips of liver, after which the eggs are sterilised.
A hole is cut out of a dressing the same size and shape as the wound. Next, this dressing is applied to the wound, providing a base for the outer dressing and protecting the surrounding skin from the proteolytic enzymes of the larvae. Approximately 10 larvae per square centimetre of lesion are then applied. The wound and larvae are covered by a fine net, which is attached with adhesive tape. An absorbent pad is placed on top of the netting. The larvae should be extracted from the wound after three days, by removing the netting and rinsing the lesion with sterile saline.
No significant risks or severe adverse events have been reported from maggot debridement. There is the possibility that an allergy may develop to the foreign protein material of the larvae, though this has not been reported. The larvae must leave the wound in order to pupate or they will die, and consequently, there is no danger of them remaining in the wound and multiplying. Some patients report a tickling/moving sensation when the dressing is in place.
Mechanism of Action
The ways in which maggots clean a wound are not fully understood but there are thought to be at least four possible mechanisms:
1. Larvae secretion of proteolytic enzymes which liquefy necrotic tissue
2. Actual ingestion of the tissue by the larvae
3. Secretions from the larvae change the wound pH
4. Bacteria are destroyed in the larval alimentary tract due to antimicrobial substances. In vitro, maggots kill or inhibit the growth of S. aureus and group A and B streptococci. Additionally, they show some activity against Pseudomonas spp.
It is suggested that larvae also stimulate the production of granulation tissue.
In vitro studies show that larval alimentary secretions have a significant effect on human fibroblasts when used in conjunction with Epidermal Growth Factor (EGF) or the cytokine Interleukin 6 (IL-6) (Prete 1997).
Maggots can quickly and efficiently debride necrotic wound tissue and promote healing. The exact mechanism of action has yet to be fully elucidated but studies suggest that larval secretions significantly amplify the effects of EGF and IL-6. Over the centuries, the benefits of larval therapy have been documented and it is becoming a re-emerging treatment option.
Bonn, D Maggot Therapy: an alternative for wound infection The Lancet 356: 1174 Sept 30 2000
Jones, M & Thomas, S Larval Therapy Nursing Standard 14(20): 47-51 Feb 2000
Prete P E, Growth effects of Phaenicia sericata larval extracts on fibroblasts: Mechanism for wound healing by maggot therapy Life Sci 60(8): 505-10 Feb 1997
Thomas S, Jones M, Shulter S, Jones S Using larvae in modern wound management Journal of Wound Care 5(2): 60-9 1996
Wayman J, Nirojogi V, Walker A, Sowinski A, Walker M A, The cost effectiveness of larval therapy in venous ulcers Journal of Tissue Viability 10(3): 91-4 Jul 2000
Wollina U, Karte K, Herold C, Looks A, Biosurgery in wound healing – the renaissance of maggot therapy Journal Eur Dermatol Venereol 14(4): 285-9 Jul 2000