Professor Hirotaka Kanuka of the Department of Tropical Medicine, Jikei University School of Medicine, in collaboration with Professor Takeshi Miyawaki of the Department of Plastic and Reconstructive Surgery, and Professor Kimiharu Iwadate of the Department of Forensic Medicine, Jikei University School of Medicine, announced on September 8 that they had successfully selected maggots suitable for maggot debridement therapy (medical treatment with maggots) and established an evaluation method using human tissue. Species identification was performed on wild maggots obtained from forensic specimens, and Lucilia sericata (common green bottle fly) was selected as being suitable for the treatment and a strain was established. Additionally, an evaluation system was successfully created to test feeding ability using surgically removed and discarded human tissue. The researchers also confirmed that the newly established strain was able to feed on more human necrotic tissue in a shorter time. These results were published in the international scientific journal Scientific Reports, and are expected to improve the effectiveness of maggot therapies.
Intractable ulcers are a condition in which blood flow becomes insufficient due to diabetes and other factors. It causes deep wounds that worsen and do not easily heal, and, if the risk of sepsis is high and antibiotics are not effective, then a treatment such as amputation is required. In Japan, 10,000 people a year end up with lower limb amputation due to intractable ulcers. The prognosis is particularly poor for patients with an amputation from the thigh, with a 5-year survival rate of 20%, and alternative treatments to amputation are being sought.
Maggot debridement therapy is a treatment for ulcers and other difficult-to-heal wounds that uses maggot flies, which feed only on necrotic tissue and secrete antibacterial substances. In Japan this treatment is not covered by medical insurance because granulation tissue hyperplasia (enlarging the tissues that fill in wounds during the healing process) can be used, without side effects, to treat ulcers caused by antibiotic-resistant bacteria. Although maggot treatment uses Lucilia sericata maggots, a type of blowfly that is aseptically produced and controlled for medical use, the strain had not been examined or evaluated.
In order to evaluate the feeding ability of maggots, the research group divided surgical surplus human tissues collected as medical waste into parts (skin, muscle, and fat), crushed each part, and prepared them as a standard feed. The tissues were fed to a standard strain of medical maggots (manufactured by the Japan Maggot Company), and their weight and developmental stage after four days from hatching were used as indices to evaluate their growth. The results showed that the maggots' degree of growth varied depending on the kind of tissue they were fed with the muscle-feeding group, the skin-feeding group, and the fat-feeding group having the highest degree of growth, in that order.
Furthermore, in order to obtain a maggot strain with a high ability to feed on human necrotic tissues, maggots were collected from 45 forensic specimens autopsied in the Department of Forensic Medicine at Jikei University School of Medicine, and then those specimens were reared. 23 maggots developed to adults, and 14 of them were Lucilia sericata. Species identification was done via morphological and genetic methods. Four pure lines with good succession were established by rearing the offspring of the Lucilia sericata that were obtained.
An evaluation system using human skin tissue was applied to these four strains of maggots and to a standard stain of medical maggots.
The results showed that one of the four strains fed the most, and had the highest weight on the fifth day after hatching, increasing to about 1.4 times the weight of the standard strain. Furthermore, this strain developed approximately one day earlier than the standard strain, and pupae and adults were larger in size.
According to Professor Kanuka, "In the future, we would like to conduct a detailed analysis of medical maggot genes and clarify how they differ from the strain we established this time. If we can identify the genes that affect their abilities, then we expect that it will be possible to create 'good maggots' by using genetic modification technology. We hope to make this technology available as soon as possible to patients who do not respond to conventional treatment methods or who are having difficulties in actual clinical practice."
Publication: Scientific Reports
Title: A human tissue-based assay identifies a novel carrion blowfly strain for maggot debridement therapy
DOI: 10.1038/s41598- 022-16253-9.
This article has been translated by JST with permission from The Science News Ltd.(https://sci-news.co.jp/). Unauthorized reproduction of the article and photographs is prohibited.