The impacts of larval density and protease inhibition on feeding in medicinal larvae of the greenbottle fly Lucilia sericata

Maggot therapy for resistant infections: the disconnect between scientific evidence, clinical acceptance and practice

OBJECTIVE

Practitioners and scientists are re-examining marginalised wound care therapies to find strategies that combat the growing problem of antimicrobial resistance (AMR) without compromising patient outcomes. Maggot therapy (MT) makes up just an estimated 0.02% of UK's National Health Service spending on wound care. This study aims to uncover why MT is not used more often, despite its affordability and high level of efficacy for both debridement and disinfection, particularly in the context of AMR infections, and to determine what can be done to ensure MT is more effectively used in the future to improve patient outcomes and manage the growing problem of AMR.

METHOD

For this investigation, a qualitative review of case studies using MT against AMR infections and a quantitative analysis of randomised control trials (RCTs) were performed using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses framework.

RESULTS

Analysis showed that MT is highly effective against a range of infections and wound types, and compares well against conventional therapies. The low use of MT may be due in part to the documented 'yuck factor', often associated with maggots as well as misconceptions around the cost, efficacy and accessibility of MT. To overcome these factors, more RCTs on the spectrum and efficacy of MT across various clinical manifestations are needed, as well as professional and public engagement campaigns.

CONCLUSION

MT is an underused therapy, particularly regarding AMR infections, and expanding its use in these circumstances appears warranted. MT could play a vital role in conserving the efficacy of the existing pool of antimicrobials available and should be considered in the development of antimicrobial stewardship programmes.

DECLARATION OF INTEREST

This work was supported by the Swansea Employability Academy, Swansea University (internal funding). The authors have no conflicts of interest to declare.

Traumatic sheep myiasis: A review of the current understanding

Myiasis, or the infestation of live humans and vertebrate animals by dipterous larvae, is a health issue worldwide. The economic impact and potential threat to animal health and wellbeing of this disease under the animal husbandry sector is considerable. Sheep are a highly vulnerable livestock category exposed to myiasis (sheep strike), due to several unique predisposing factors that attract flies. The successful mitigation of this disease relies on a thorough understanding of fly population dynamics associated with the change in weather patterns and the evaluation of this disease through different branches of science such as chemistry, molecular biology, and microbiology. The present review provides a summary of the existing knowledge of strike in sheep, discussed in relation to the application of volatile organic compounds, metagenomics, and molecular biology, and their use regarding implementing fly control strategies such as traps, and to increase the resilience of sheep to this disease through improving their health and wellbeing.

A molecular approach to maggot debridement therapy with Lucilia sericata and its excretions/secretions in wound healing

Chronic wounds caused by underlying physiological causes such as diabetic wounds, pressure ulcers, venous leg ulcers and infected wounds affect a significant portion of the population. In order to treat chronic wounds, a strong debridement, removal of necrotic tissue, elimination of infection and stimulation of granulation tissue are required. Maggot debridement therapy (MDT), which is an alternative treatment method based on history, has been used quite widely. MDT is an efficient, simple, cost-effective and reliable biosurgery method using mostly larvae of Lucilia sericata fly species. Larvae can both physically remove necrotic tissue from the wound site and stimulate wound healing by activating molecular processes in the wound area through the enzymes they secrete. The larvae can stimulate wound healing by activating molecular processes in the wound area through enzymes in their excretions/secretions (ES). Studies have shown that ES has antibacterial, antifungal, anti-inflammatory, angiogenic, proliferative, hemostatic and tissue-regenerating effects both in vivo and in vitro. It is suggested that these effects stimulate wound healing and accelerate wound healing by initiating a direct signal cascade with cells in the wound area. However, the enzymes and peptides in ES are mostly still undefined. Examining the molecular content of ES and the biological effects of these ingredients is quite important to illuminate the molecular mechanism underlying MDT. More importantly, ES has the potential to have positive effects on wound healing and to be used more as a therapeutic agent in the future, so it can be applied as an alternative to MDT in wound healing.

Microbiome pattern of Lucilia sericata (Meigen) (Diptera: Calliphoridae) and feeding substrate in the presence of the foodborne pathogen Salmonella enterica

The microbial diversity and quantitative dynamics during the insect’s development stages constitute recently developed putative tools in forensic and medical studies. Meanwhile, little is known on the role of insects in spreading foodborne pathogenic bacteria and on the impact of these pathogens on the overall insects and feeding substrate microbiome composition. Here, we provide the first characterization of the bacterial communities harbored in adult and immature stages of Lucilia sericata, one of the first colonizers of decomposed human remains, in the presence of the foodborne pathogen Salmonella enterica using 16S rRNA Illumina sequencing and qPCR. The pathogen transmission from the wild adults to the second generation was observed, with a 10^1.25× quantitative increase. The microbial patterns from both insect and liver samples were not influenced by the artificial introduction of this pathogenic foodborne bacteria, being dominated by Firmicutes and Proteobacteria. Overall, our results provided a first detailed overview of the insect and decomposed substrate microbiome in the presence of a human pathogen, advancing the knowledge on the role of microbes as postmortem interval estimators and the transmission of pathogenic bacteria.

Effect of density and species preferences on collective choices: an experimental study on maggot aggregation behaviours

Collective decisions have been extensively studied in arthropods, but they remain poorly understood in heterospecific groups. This study was designed to (1) assess the collective behaviours of blow fly larvae (Diptera: Calliphoridae) in groups varying in density and species composition, and (2) relate them to the costs and benefits of aggregating on fresh or decomposed food. First, experiments testing conspecific groups of Lucilia sericata and Calliphora vicina larvae, two species feeding at the same time on fresh carcasses, demonstrated decreases in growth and survival on rotten beef liver compared with fresh liver. However, mixing species together reduced this adverse impact of decomposition by increasing the mass of emerged adults. Second, larval groups were observed in binary choice tests between fresh and rotten liver (i.e. optimal and sub-optimal food sources). The results showed that larvae interacted with each other and that these interactions influenced their food preferences. We observed that (1) larvae were able to collectively choose the optimal food, (2) their choice accuracy increased with larval density and (3) the presence of another species induced a reversal in larval preference towards rotten food. These results highlight the ubiquity of collective decision properties in gregarious insects. They also reveal an unexpected effect of interspecific association, suggesting the colonization of new resources through a developmental niche construction.

Benefits of heterospecific aggregation on necromass: influence of temperature, group density, and composition on fitness-related traits

Necrophagous blowflies (Diptera: Calliphoridae) such as Calliphora vicina, a cold-tolerant species, and Lucilia sericata, a warm-adapted species, are pioneer carrion-breeder. Although these two species have different temperature preferences, larvae aggregate actively and often feed simultaneously on carrion. The hypothesis to be tested was that L. sericata benefits from the association with C. vicina at lower temperatures (i.e., 15 °C) and that C. vicina derives greater benefits from this association at higher temperatures (i.e., 28 °C). Therefore, both species were raised at these two constant temperatures from first instars to adults under three different conditions: monospecific low-density, monospecific high-density, and heterospecific high-density. The time until larval migration, surface area of puparia, and survival rates were determined for each condition. Differences between these fitness-related traits were found between species, temperatures, group densities, and species compositions. At 28 °C, C. vicina larvae bred in heterospecific groups migrated significantly earlier and in higher numbers than that under same density conspecific conditions, with a lower mortality rate. At 15 °C, both species benefited from high-density heterospecific associations, expressed by faster development and larger puparia. In conclusion, necrophagous larvae benefited from heterospecific aggregations at suboptimal temperatures by adapting their migration time to that of the faster species. Since temperature changes throughout the day and over the year, the beneficiary of such a collective association also changes. The costs involved and deviations to the temperature-size rule highlight the complexity of the carrion ecosystem.

New Insights Into Culturable and Unculturable Bacteria Across the Life History of Medicinal Maggots Lucilia sericata (Meigen) (Diptera: Calliphoridae)

Because of the nutritional ecology of dung- and carrion-feeding, bacteria are the integral part of Lucilia sericata life cycle. Nevertheless, the disinfected larvae of the blowfly are applied to treat human chronic wounds in a biosurgery named maggot debridement therapy (MDT). To realize the effects of location/diet on the gut bacteria, to infer the role of bacteria in the blowfly ecology plus in the MDT process, and to disclose bacteria circulating horizontally in and vertically between generations, bacterial communities associated with L. sericata specimens from various sources were investigated using culture-based and culture-independent methods. In total, 265 bacteria, including 20 families, 28 genera, and 40 species, were identified in many sources of the L. sericata. Culture-dependent method identified a number of 144 bacterial isolates, including 21 species, in flies reared in an insectary; specimens were collected from the field, and third-instar larvae retrieved from chronic wounds of patients. Metagenetic approach exposed the occurrences of 121 operational taxonomic units comprising of 32 bacterial species from immature and adult stages of L. sericata. Gammaproteobacteria was distinguished as the dominant class of bacteria by both methods. Bacteria came into the life cycle of L. sericata over the foods and transovarially infected eggs. Enterococcus faecalis, Myroides phaeus, Proteus species, Providencia vermicola, and Serratia marcescens were exchanged among individuals via transstadial transmission. Factors, including diets, feeding status, identification tool, gut compartment, and life stage, governed the bacteria species. Herein, we reemphasized that L. sericata is thoroughly connected to the bacteria both in numerous gut compartments and in different life stages. Among all, transstadially transmitted bacteria are underlined, indicating the lack of antagonistic effect of the larval excretions/secretions on these resident bacteria. While the culture-dependent method generated useful data on the viable aerobic gut bacteria, metagenomic method enabled us to identify bacteria directly from the tissues without any need for cultivation and to facilitate the identification of anaerobic and unculturable bacteria. These findings are planned to pave the way for further research to determine the role of each bacterial species/strain in the insect ecology, as well as in antimicrobial, antibiofilm, anti-inflammatory, and wound healing activities.

The maggot therapy supply chain: a review of the literature and practice

Maggot therapy (MT) is the clinical application of living fly larvae for the treatment of non-healing wounds and wounds that require debridement. This systematized and expanded literature review is the first study to investigate MT through the conceptual and disciplinary framework of supply chain management. The review of 491 selected academic papers was expanded to include the grey literature and online information resources to construct a first-pass theory of the medicinal maggot supply chain. It shows that the literature to date has focused on isolated discussions of echelon-specific issues such as diet improvement and sterilization protocols in the production echelon, and the relative effectiveness of medicinal maggot application methods in the treatment echelon. There is little knowledge in the public domain regarding the transport and distribution of medicinal maggots, but existing supply chains for vaccines, blood and pathology specimens may provide learning and supply chain integration opportunities. Maggot therapy knowledge across the treatment echelon is generally substantive but there is still insufficient knowledge regarding patients' and health care providers' attitudes toward the therapy, and their experiences of receiving and administering MT. Moreover, there is no research concerned with the humane disposal of medicinal flies during production and after treatment.

Expression of a New Recombinant Collagenase Protein of Lucilia Sericata in SF9 Insect Cell as a Potential Method for Wound Healing

BACKGROUND

Today, the use of maggot therapy has become widespread due to the increase in chronic ulcers in the world. The recombinant production of secreted enzymes from these larvae is a novel non-invasive method for the treatment of chronic ulcers. Lucilia Sericata (L. sericata) collagenase (MMP-1) has been expressed in insect cells. Collagenase is an enzyme that is widely used in clinical therapy and industry. It has been indicated that collagenase is expressed and secreted in salivary glands of L. sericata while using for maggot debridement therapy.

OBJECTIVES

In the present study we decided to produce the recombinant form of collagenase enzyme in Spodoptera frugiperda (SF9) insect cells using the baculovirus expression system (Bac-to-Bac).

MATERIALS AND METHODS

cloned the coding sequences (residues 494-1705) of L. sericata collagenase into the pFastBacHTA as donor plasmid. After transposition in the bacmid of DH10Bac host, the bacmid was transfected into the Sf9 cell line, then the expressed recombinant collagenase (MMP-1) was purified using the Ni-NTA agarose.

RESULTS

The recombinant protein was verified by Western blotting. Furthermore, the biological activity of purified protein was measured in the presence of its specific substrate and its inhibitor, which was 67 IU.mL-1 based on our results, it was revealed that the characterized gene in our previous study codes L. sericata collagenesa enzyme.

CONCLUSION

Considering to the broad applications of collagenase in medical sciences, for the first time, we cloned the L. sericata collagenase (MMP-1) gene into the insect cell line to establish a method for the expression and purification of L. sericata collagenase (MMP-1). The result help for preparing and designing a safe and versatile recombinant drug in future.

Facing death together: heterospecific aggregations of blowfly larvae evince mutual benefits

Heterospecific aggregations and foraging associations have been observed between different species, from apes to birds to insects. Such associations are hypothesized to result in a mutually beneficial relationship entailing benefits that are not apparent in conspecific groupings. Therefore, the objectives of the present study were to investigate 1) how 3 blowfly species, namely, Calliphora vicina, Calliphora vomitoria, and Lucilia sericata, aggregate according to species, and 2) if developmental benefits are linked to heterospecific aggregation. For objective (1), larvae of 2 species were placed between 2 conspecific aggregates, each with a different species (i.e., a binary choice test). After 20 h, the positions of all larvae were determined. On average, 98% of the maggots added later settled together on one of the 2 pre-existing aggregations, demonstrating a collective choice. The aggregation spot with C. vicina was preferred against others, indicating different attractiveness of different species. To relate this behavior to its benefits (objective ii), C. vicina and L. sericata larvae were raised from first instar to adult in con- and heterospecific conditions, and their development time, mortality rates, and morphometrics were measured. Thereby, mutual and asymmetric consequences were observed: specifically, there were significant increases in size and survival for L. sericata and faster development for C. vicina in heterospecific groups. These results indicate that the predilection for heterospecific association leads to mutual developmental benefits. This heterospecific aggregation behavior may be a resource-management strategy of blowflies to face carrion-based selection pressure.

In vitro evaluation of the association of medicinal larvae (Insecta, Diptera, Calliphoridae) and topical agents conventionally used for the treatment of wounds

Wound healing is a complex process involving multiple biochemical and cellular events and represents a neglected public health issue. As a consequence, millions of people worldwide suffer from chronic wounds. The search for new treatment alternatives is therefore an important issue. In the context of wound healing, Maggot Debridement Therapy (MDT) is an inexpensive treatment with few contraindications and very promising results. This study aimed to evaluate the in vitro feasibility and implications of larvae (= MDT) use when combined with topical agents as a strategy to identify additive or synergistic combinations. The weight and survival rate of Cochliomyia macellaria (Fabricius) (Insecta, Diptera, Calliphoridae) larvae reared in an in vitro wound with either honey, hydrogel, 10% papain gel, essential fatty acids (EFA), collagenase, or silver sulfadiazine were evaluated after 24, 48 and 72 h. Hydrogel (for weight: 24 and 72 h; for survival: 24 h) and 10% papain gel (for weight: 48 h; for survival: 48 and 72 h) demonstrated the least interference in larval weight gain and survival rate, when compared to the control group. The results obtained in this study showed that the combined use of larvae and hydrogel or 10% papain gel may be promising to maximize the tissue repair. Honey, EFA and collagenase could be used to prepare the bed of the dry wounds to receive the MDT.

What is the optimal treatment time for larval therapy? A study on incubation time and tissue debridement by bagged maggots of the greenbottle fly, Lucilia sericata

The effective use of larvae of the greenbottle fly, Lucilia sericata, in wound debridement requires a working knowledge of how feeding changes over time. Using a laboratory assay and bagged larval dressings, the effect of incubation time on larval feeding rates and body mass was investigated for up to 120 hours at 32°C. The mass of tissue digested increased significantly in incremental 24-hour periods up to 72 hours, with no significant consumption occurring afterwards. Larval mass increased only up to 48 hours. A further test comparing the efficacy of a single 96-hour application of larvae against two consecutive 48-hour applications found that the mass of tissue digested in the latter was 14.3% higher than the former, a difference that was statistically significant. Current clinical guidance suggests a 4-day application period for bagged larvae. Based on these results, an incubation time of 72 hours (3 days) for bagged larvae would be the most effective at the study temperature. However, it is acknowledged that wound temperature can vary, whereby feeding rates would likely differ. In view of this, we conclude that a period of 3 to 4 days is optimum for the application of larvae, and current guidelines should be adhered to.

Mixed-species aggregations in arthropods

This review offers the first synthesis of the research on mixed-species groupings of arthropods and highlights the behavioral and evolutionary questions raised by such behavior. Mixed-species groups are commonly found in mammals and birds. Such groups are also observed in a large range of arthropod taxa independent of their level of sociality. Several examples are presented to highlight the mechanisms underlying such groupings, particularly the evidence for phylogenetic proximity between members that promotes cross-species recognition. The advantages offered by such aggregates are described and discussed. These advantages can be attributed to the increase in group size and could be identical to those of nonmixed groupings, but competition-cooperation dynamics might also be involved, and such effects may differ between homo- and heterospecific groups. We discuss three extreme cases of interspecific recognition that are likely involved in mixed-species groups as vectors for cross-species aggregation: tolerance behavior between two social species, one-way mechanism in which one species is attractive to others and two-way mechanism of mutual attraction. As shown in this review, the study of mixed-species groups offers biologists an interesting way to explore the frontiers of cooperation-competition, including the process of sympatric speciation.

To eat or get heat: Behavioral trade-offs between thermoregulation and feeding in gregarious necrophagous larvae

The thermoregulation behavior of Lucilia sericata larvae (Diptera: Calliphoridae), a necrophagous species that feeds on vertebrate cadavers, was investigated. These larvae require high heat incomes to develop, and can elevate temperatures by forming large aggregates. We hypothesized that L. sericata larvae should continue to feed at temperatures up to 38 °C, which can be reached inside larval masses. Thermal regulation behavior such as movement between a hot food spot and colder areas was also postulated. The hypotheses were tested by tracking for 1 h the activity of single, starved third instar larvae in a Petri dish containing 1 food spot (FS) that was heated to a constant temperature of 25 °C, 34 °C or 38 °C with an ambient temperature of 25 °C. The influence of previous conspecific activity in the food on larval behavior was also tested. The crops of larvae were dissected to monitor food content in the digestive systems. Based on relative crop measurements, larvae fed at all food temperatures, but temperature strongly affected larval behavior and kinematics. The total time spent by larvae in FS and the duration of each stay decreased at high FS temperature. Previous activity of conspecifics in the food slightly increased the time spent by larvae in FS and also decreased the average distance to FS. Therefore, necrophagous L. sericata larvae likely thermoregulate during normal feeding activities by adjusting to local fluctuations in temperature, particularly inside maggot masses. By maintaining a steady internal body temperature, larvae likely reduce their development time.

Flying maggots: a smart logistic solution to an enduring medical challenge

Purpose

Whilst there is a growing body of research which discusses the use of remotely piloted aircraft systems (RPAS) (otherwise known as “drones”) to transport medical supplies, almost all reported cases employ short range aircraft. The purpose of this paper is to consider the advantages and challenges inherent in the use of long endurance remotely piloted aircraft systems (LE-RPAS) aircraft to support the provision of medical supplies to remote locations – specifically “medical maggots” used in maggot debridement therapy (MDT) wound care.

Design/methodology/approach

After introducing both MDT and the LE-RPAS technology, the paper first reports on the outcomes of a case study involving 11 semi-structured interviews with individuals who either have experience and expertise in the use of LE-RPAS or in the provision of healthcare to remote communities in Western Australia. The insights gained from this case study are then synthesised to assess the feasibility of LE-RPAS assisted delivery of medical maggots to those living in such geographically challenging locations.

Findings

No insuperable challenges to the concept of using LE-RPAS to transport medical maggots were uncovered during this research – rather, those who contributed to the investigations from across the spectrum from operators to users, were highly supportive of the overall concept.

Practical implications

The paper offers an assessment of the feasibility of the use of LE-RPAS to transport medical maggots. In doing so, it highlights a number of infrastructure and organisational challenges that would need to be overcome to operationalise this concept. Whilst the particular context of the paper relates to the provision of medical support to a remote location of a developed country, the core benefits and challenges that are exposed relate equally to the use of LE-RPAS in a post-disaster response. To this end, the paper offers a high-level route map to support the implementation of the concept.

Social implications

The paper proposes a novel approach to the efficient and effective provision of medical care to remote Australian communities which, in particular, reduces the need to travel significant distances to obtain treatment. In doing so, it emphasises the importance in gaining acceptance of both the use of MDT and also the operation of RPAS noting that these have previously been employed in a military, as distinct from humanitarian, context.

Originality/value

The paper demonstrates how the use of LE-RPAS to support remote communities offers the potential to deliver healthcare at reduced cost compared to conventional approaches. The paper also underlines the potential benefits of the use of MDT to address the growing wound burdens in remote communities. Finally, the paper expands on the existing discussion of the use of RPAS to include its capability to act as the delivery mechanism for medical maggots.

Quality control of a medicinal larval (Lucilia sericata) debridement device based on released gelatinase activity

Lucilia sericata Meigen (Diptera: Calliphoridae) larvae are manufactured worldwide for the treatment of chronic wounds. Published research has confirmed that the primary clinical effect of the product, debridement (the degradation of non-viable wound tissue), is accomplished by a range of enzymes released by larvae during feeding. The quality assessment of larval activity is currently achieved during production using meat-based assays, which monitor insect growth and/or the reduction in substrate mass. To support this, the present authors developed a complementary radial diffusion enzymatic assay to produce a visual and measureable indication of the activity of larval alimentary products (LAP) collected under standardized conditions, against a gelatin substrate. Using basic laboratory equipment and reagents, the assay is rapid and suited to high throughput. Assay reproducibility is high (standard deviation: 0.06-0.27; coefficient of variation: 0.75-4.31%) and the LAP collection procedure does not adversely affect larval survival (mortality: < 2%). Because it is both cost- and time-effective, this method is suited to both academic and industrial use and supports good manufacturing and laboratory practice as a quality control assay.

Endotoxin testing of a wound debridement device containing medicinal Lucilia sericata larvae

Alimentary products of medicinal Lucilia sericata larvae are studied to determine their mechanisms of action, particularly in the contexts of wound debridement and disinfection. Furthermore, the larvae can be applied to patients in contained medical devices (such as the BioBag; BioMonde). Here, we tested the materials and larval content of the most commonly used debridement device (the "BB-50") to explore the possibility that endotoxins may be contributing to the bio-activity of the product, given that endotoxins are potent stimulants of cellular activation. Using standardised protocols to collect larval alimentary products (LAP), we proceeded to determine residual endotoxin levels in LAP derived from the device, before and after the neutralisation of interfering enzymatic activity. The debridement device and its associated larval content was not a significant source of lipopolysaccharide (LPS) activity. However, it is clear from these experiments that a failure to remove the confounding serine proteinase activity would have resulted in spuriously high and erroneous results. The residual LPS levels detected are unlikely to be active in wound healing assays, following cross-referencing to publications where LPS at much higher levels has been shown to have positive and negative effects on processes associated with wound repair and tissue regeneration.

Interspecific shared collective decision-making in two forensically important species

To date, the study of collective behaviour has mainly focused on intraspecific situations: the collective decision-making of mixed-species groups involving interspecific aggregation-segregation has received little attention. Here, we show that, in both conspecific and heterospecific groups, the larvae of two species (Lucilia sericata and Calliphora vomitoria, calliphorid carrion-feeding flies) were able to make a collective choice. In all groups, the choice was made within a few minutes and persisted throughout the period of the experiment. The monitoring of a focal individual within a group showed that these aggregations were governed by attractive and retentive effects of the group. Furthermore, the similarity observed between the conspecific and heterospecific groups suggested the existence of shared aggregation signals. The group size was found to have a stronger influence than the species of necrophagous larvae. These results should be viewed in relation to the well-known correlation between group size and heat generation. This study provides the first experimental examination of the dynamics of collective decision-making in mixed-species groups of invertebrates, contributing to our understanding of the cooperation-competition phenomenon in animal social groups.