Maggot Therapy “Use of Fly Larvae for Treatment of Wounds”- A Review

Several chronic wounds require alternative therapy in addition to the conventional ones. Maggot therapy (MT) is one of these alternatives. MT is one form of animal-based treatment options known as Biotherapy (medicinal use of live organisms). MT or Maggot debridement therapy (MDT) is the medical use of live maggots for cleaning chronic, non-healing wounds or certain wounds that are not amenable to other forms of therapy. MT is achieved through maggots' secretion of proteolytic enzymes that liquefy the necrotic tissues and then feed on such tissues (wound debridement activity), wound disinfection (antimicrobial) activity and growth-promoting (wound healing) activity.  MT has been used for centuries.  Occasionally used since the 1930’s and early 1940’s and then in 2004, the Food and Drug Administration (FDA) approved maggots as a medical device that has been prescribed for patients in more than 200 hospitals in the United States.  This article presents a review of published articles on the different aspects of MT  (mainly the past and current uses, maggots used, how to apply maggots for wound treatments,  advantages and disadvantages,  problems and adverse reactions and its  application  in Egypt) that serves as a guide to health professionals who may be users  of this  form of  treatment now and in the  future


INTRODUCTION
Maggots or fly larvae (Order Diptera) are often highly specialized for living in a wet environment and very few are adapted to dry conditions. A few species are internal parasites of animals or humans. When maggots infest humans or other vertebrates, it is called myiasis. Myiasis is classified based on the type of tissue attacked or the site of infestation (Hosni et al., 2019). Flies causing myiasis are either obligate parasites that develop only on live hosts or facultative parasites that develop on either live hosts or carrion (Zumpt, 1965 andHall andWall, 1995). The naturally-occurring myiasis can be beneficial, but sometimes it can be harmful, depending upon the type of maggots and the circumstances surrounding the infestation. The known beneficial applications of myiasis are: (1) the use of maggots that feed on human corpses to give an indication of the time that elapsed since death, as well as the place of death "Forensic Entomology" or the legal use of such maggots to help solve crimes (Byrd and Castner, 2010)) and (2) for treatment of wounds "Maggot therapy (Bonn, 2000 andThomas, 2003).
Maggot therapy (MT) is one form of animal-based treatment options known as Biotherapy (medicinal use of live organisms) which includes also those of the honey bee (Apitherapy),leech (Hirudotherapy), fish (Ich thiotherapy), worm (Helmitherapy), pets (Animal-assisted therapy) and Phage (Microbialtherapy). Maggot therapy "Larva therapy, Biosurgery or Maggot debridement therapy (MDT)" is the medical use of live maggots for cleaning human chronic and non-healing wounds or certain wounds that are not amenable to other forms of therapy (Sherman et al., 2000;Church and Courtenay, 2002;Tantawi et al., 2007Tantawi et al., & 2010Gupta, 2008;Hall, 2010;Marineau et al., 2011;Sherman, 2014a;Naik andHarding, 2017 andYan et al., 2018). It involves allowing maggots of certain species of blowflies (Family: Calliphoridae) to consume the necrotic tissue in the wound, and to produce antibiotic substances that kill the pathogenic bacteria and promote tissue healing (Sherman et al., 2000;Nigam et al, 2006a & b;Tantawi et al., 2010 andYan et al, 2018). MT is also used for veterinary purposes. Human and veterinary case histories were reviewed by Hinshaw (2000) and Zarchi and Jemec (2012).
This article presents an overview of the research evidence on the past and current uses of MT that serves as a guide to health professionals who may be users of this form of treatment now and in the future.

MATERIALS AND METHODS
This article is based primarily on a series of lectures presented by the first author for undergraduate students at the Department of Entomology, Faculty of Science, Ain Shams University, Cairo. Moreover, a systematic search and review of the available published articles on the different aspects of MT using "Wound debridement, MDT, MT, and Lucilia maggots" as keywords were performed on Pub Med and internet-based ones. In addition, several related web pages were accessed. Moreover, the studies carried out in Egypt were added and discussed. A total of 66 articles of the different MT aspects were included in this review.

RESULTS AND DISCUSSION Brief History and Current Status:
The early history of maggots in wound care was reviewed by Goldstein in 1932 (Thomas, 2003). During the 1930's and early1940's, MT was extensively performed by thousands of physicians. By the mid-1940s, once penicillin was discovered and antibiotic therapy became common world-wide, MT had virtually ceased, except as a treatment of last resort. Later, MT was occasionally used during the 1970's for skin and soft tissue wounds which did not respond to surgery and antibiotic therapy. With the emergence of antibacterial-resistant strains of microbes, the recent interest in maggots re-emerged in 1982. From 1989 on, MT has been reintroduced for the treatment of wounds in the USA, Canada, Great Britain, and some other European and Asian countries. Maggot therapy was offered in around 50 hospitals throughout the UK, for various conditions, ranging from burns to aiding recovery after surgery (Mumcuoglu et al.,19 99).
In 2004, the Food and Drug Administration (FDA) granted permission and approved maggots as a medical device to be marketed for wound care (Sherman, 2005;Andersen et al., 2010;Cazander et al., 2010;Choudhary et al., 2016;and Yan et al, 2018) which has been prescribed for patients in more than 200 hospitals in the USA. It was reported that thousands of patients have been treated by this method (Mumcuoglu, 2001) as for e.g., some 20,000 patients throughout the UK have benefited from MT (Brindley. 2004). Currently, there are 12 laboratories in some countries dispensing maggots at low cost (Marineau et al , 2011).

Maggots Used for Medical Applications:
While many species of fly larvae have been recorded to cause human myiasis, only a relatively small number (Francesconi and Lupi, 2012) are known to have been used medicinally. The use of some facultative calliphorids (e.g., the black bottle blowfly, Phormia regina) has been described in the literature. Today, the recommended and widely used therapeutic maggots are those of Lucilia (= Phaenicia) sericata, the green bottle blowfly (Sherman et al., 2000 andNigam et al., 2006a); a facultative parasite that, in humans, only attacks necrotic tissues and do not burrow down into live flesh . Moreover, Lucilia cuprina showed effectiveness in the treatment of diabetic foot wounds (Paul et al., 2009;Tantawi et al., 2010 andHassan et al. 2014). Clearly, considerable caution should be taken when selecting any other species of maggots for medicinal use as some calliphorids, however, cannot be used therapeutically for e.g., Cochliomyia macellaria, Cochliomyia hominovorax (screwworms) and Chrysomya megacephala (the common green bottle fly or oriental latrine fly) since they will attack healthy human tissues.

Production of the Medicinal Maggots:
Early, non-sterile larvae of L. sericata were produced and used to promote wound debridement and disinfection. Although these were nonsterile, no serious adverse reactions (except tetanus) were reported. However, it was reported that for successful larval therapy, the maggots should be free of bacteria before being placed into wounds.
To obtain medicinal maggots, eggs collected from specially bred adult blowflies are sterilized by washing in a dilute solution of sodium hypochlorite (5%), rinse in sterile water, agitate in 4% formaldehyde and then the eggs are rinsed and allowed to hatch on fresh liver or on sterile meat-agar media. Several facilities producing sterile maggots have been established in the USA and some other countries. Since 1995, Biosurgical Research Unit (BRU, Princess of Wales Hospital), in Bridgend, UK is producing sterile maggots under the brand name of LarvE and supplying 1300 centers throughout the UK and Europe.

Methods of Applications:
Before application, the wound is cleaned with normal salt solution or sterilized water to remove the grease and dirt (Baer. 2011). Maggots are applied on the wound in two-ways (Choudhary et al., 2016): the free-range dressing (direct contact method) and the biobag dressing (indirect contact method) (Janssen, 2005;Jones and Wall, 2007;Lepage et al. 2012 andBrown, 2013).
In the free-range dressing, maggots are applied directly to the wound for 3 days and allowed to roam freely (Brown, 2013) over the surface seeking out areas of necrotic tissue but due to which, maggots can escape out from the wound site (Choudhary et al., 2016), while in biobag dressing, the maggots are enclosed in a net pouch containing a piece of hydrophilic polyurethane foam, which is placed directly upon the wound surface, so that maggots cannot escape dressing (Jones and Wall, 2007).
For biobag dressing (Fig. 1), sterile first instar larvae of L. sericata are applied to the wound sealed in with a bandage (Janssen, 2005;Naik and Harding, 2017) and left to feed for 2-3 days and then removed and replaced with fresh ones. The old larvae are removed simply by detaching the outer dressing and collecting them with forceps or flushed out of the wound with sterile saline (Baer. 2011). The treatment is repeated until the wound is clean or the healthy tissue has formed. The healthy skin surrounding the ulcer is covered with a hydrocolloid dressing to protect it from the proteolytic enzymes produced by the larvae and to eliminate the tickling sensation caused by the maggots' movements (Baer. 2011). For this, the wound is measured and cuts out a sample of a barrier like Duoderm, creating a frame around the wound then maggots are contained within the area of the wound under a fine mesh net (chiffon) so there is a little cage for the maggots, which prevents their escape. The edges are secured with a tape. Moist gauze swabs are placed over the net and changed on a daily basis to prevent the larvae from drying out. Maggots are obligatory airbreathers so that the dressing must allow fresh air to enter the area and let the liquefied necrotic tissue to drain freely from the wound (Dar et al., 2013;Dholaria et al., 2014 andSherman, 2014b).
The number of maggots applied to a wound depends upon the amount of necrotic tissue present, wound depth, and width of wound area (Lepage et al. 2012 andAbdolmaleki et al., 2015). Typically, five to 10 larvae per square centimeter of the wound (Sherman, 2009 andSingh et al., 2014) are used twice a week. It is more cost-effective to use a large number of maggots for a short period of time than a small number for an extended period. The period of time necessary for maggot debridement of a wound depends on a number of factors, including (1) The depth and extent of the wound, (2) The part of the body affected, and (3) The number of maggots present in the wound. However, the maggots should be removed immediately once they have removed all the dead tissue and before they have become established in healthy tissue.

Fig.1:
Maggots' application to a wound: (1) an injury on the arm before applying MT, (2) a large dressing (like a plaster) is placed over the wound first, (3) saltwater is added to the maggots to wash them, (4) maggots are then emptied out onto a piece of net so that the saltwater drained away, (5) the net is turned over and placed on the wound and stuck down and (6) the maggots stay on the wound for 2-3 days (Modified from Jones, 2004).

Wound Management:
It was observed that maggots are capable of entering any part of the wound wherever necrotic tissue exists and clean minute areas without harming healthy tissue in a manner resembling microsurgery; a task which is very difficult to attain by the conventional surgery.
Although maggot therapy can be applied to most cavity wounds, they are not recommended for use in wounds that might connect with the body cavity or important internal structures or organs. As a precautionary measure, it is also advised that they should not be applied near to exposed major blood vessels How Do the Maggots work? "Mechanisms of Action": Although it is not fully understood how the maggots work, however, different mechanisms of wound healing by maggots were suggested and including: 1. Wound debridement activity: maggots secrete proteolytic enzymes (Casu et al., 1996 andHonda et al,. 2011) that liquefy the necrotic tissues into a semi-liquid substance and then feed on these tissues. 2. Antimicrobial activity "Wound disinfection" through (a) the presence and activity of the larvae increasing the exudates from the host wound which mechanically washes the bacteria out of the wounds (Vowden andVowden, 2003 andMarineau et al., 2011), (b) the destruction of bacteria in the wound by maggots excretions which contain anti-bacterial substances (Pavillard and Wright, 1957;Greenberg, 1968;Mumcuoglu et al, 2001;Kruglikova and Chernysh, 2011;Poeppel et al., 2015 andYan et al. 2018) and (c) maggot secretion of ammonia (Guerrini, 1988) that rises wound pH (from acidic to alkaline) which may partly contribute to wound disinfection. 3. Growth promoting activity "Wound healing" (Marineau et al., 2011 andSherman, 2014b) through (a) larvae secrete substances with wound healing properties (such as allantoin and urea) which also have antimicrobial activity and (b) the continuous crawling action of the larvae stimulates the formation of healthy granulation tissue which may actually lead wounds to heal more quickly.

Factors Influencing Maggot Survival within a Wound:
1. Systemic antibiotic therapy: Maggots may sometimes be applied to treat wounds in patients who are receiving antibiotic therapy. It was observed that antibiotics have adverse effects on maggot growth and development so that maggots should not be applied to patients on antibiotic therapy. 2. Topical treatments: Because MT is not generally regarded as the firstline treatment, the wounds to which MT is applied may have previously been treated with numerous products, e.g. amorphous hydrogels. Studies have indicated that some hydrogels markedly inhibit Lucilia maggot survival and growth (Thomas and Andrews, 1999), so that all traces of such products need to be removed from a wound prior to the application of maggots. 3. X-rays have no effects on larval development, indicating that maggots do not have to be removed from wounds prior to X-ray investigations. Advantages and Disadvantages A.Advantages: 1. It is a rapid, more effective treatment of infected and necrotic wounds than many of the other treatments commonly prescribed.  (Vowden and Vowden, 2003). 7. Effectiveness is limited by the environment (wound pH, fluid, and oxygen).

Problems and Adverse Reactions
Although no serious side effects were noted following the use of magg ots, there are some minor reactions have been described: 1. Transient pyrexia and bleeding in a very few cases. 2. Pain and physical discomfort that varies from a mild sensation to severe pain that may lead to termination of the treatment. 3. Ammonia toxicity resulting from the absorption of maggot-secreted ammonia into the bloodstream leading to a rapid rise in temperature and respiratory rate, accompanied by loss of weight and appetite of the animals (Guerrini, 1988). Ammonia toxicity is theoretically possible in humans, although maggot therapy utilizes far fewer larvae. 4. Failure of maggots to survive on the wound as a result of maggots' drowning due to poor drainage of the exudates from the wound or unsuitable pH of the wound for the young larvae and its proteolytic enzymes.

Situation and Use of Maggot Therapy in Egypt:
The first study on the application of MT for wound debridement in Egypt was that on animals by Eve Iversen (Iversen, 2000). Moreover, Hassan et al. (2014) used L. cuprina maggots for treatment of an artificial wound made in a diabetic foot of rabbit and observed that the wound was completely healed after 13 days.
For humans, Tantawi et al. (2010) reported that L. cuprina proved to be safe and effective in healing the diabetic foot wounds of two patients at Alexandria Main University Hospital (AMUH) and Tantawi et al. (2017) used L. sericata for treatment of 14 bed-bound patients with pressure ulcers at AMUH. Since 2000, MT has been practiced at AMUH and more than 250 patients had their venous and diabetic wounds were successfully treated using disinfected maggots of L. sericata (Tantawi, 2004).
CONCLUSION Maggot therapy proved to be effective in the treatment of a wide variety of necrotic wounds / ulcers and antibioticresistant ones than some of the other treatments commonly prescribed. Maggots of L. sericata are mainly used for such purpose due that in humans, they attack only necrotic tissues and do not burrow down into live flesh. Considerable caution should be taken when selecting any other species of maggots for medicinal use for e.g., some Calliphoridae as Cochliomyia macellaria, C. hominovorax, and Chrysomya megacephala cannot be used since they will attack healthy tissues. Such method of wound treatment is easy to apply and do not require a specialist and has a positive impact upon patients' quality of life as it decreases the number of hospital visits and prevents the need for hospital admission and thus reduces treatment costs.