Project Description

Background

Scabies is a disease that has persisted through the ages. Often associated with past eras, particularly with lower socioeconomic classes, poor hygiene, and uncleanliness, it is actually on the rise in recent times. Contrary to these false beliefs, this disease is transmitted by direct and long-lasting contact, which is why this upturn has been observed in the aftermath of the pandemic 1.

The World Health Organization (WHO) estimates that approximately 200 million people worldwide suffer from scabies, with a cumulative total of 400 million affected each year 2. This health issue is widespread across Europe and is particularly affecting our local community in Barcelona, where scabies outbreaks have become increasingly common, with the number of people affected rising year on year from 2021 onwards 3.

Figure 1. Representation of how scabies affects people around the world.

Figure 2. Scabies outbreaks from 2015 to 2023.

This contagious disease is caused by a mite called Sarcoptes scabiei, which, by means of grooves it creates up to the epidermis, lays its eggs. The mite itself, the grooves, eggs, excrement, and debris caused by the parasite are what provoke the hypersensitivity reaction that results in the characteristic redness, pimples, flaking, and itching of the skin 4.

Current treatments, such as topical permethrin or oral ivermectin, often have adverse side effects and are not suitable for preventive use, as they are applied once scabies has been diagnosed in the patient 5. In addition, there are groups within the population where these pharmacological treatments are not recommended or not authorized. In the case of children under 2 months of age, topical permethrin is not authorized because of the potential risk of neurotoxicity (due to increased percutaneous absorption). The other case is pregnant women, in whom these treatments are not recommended 6. Therefore, we propose an innovative approach involving the use of synthetic biology to develop a new and effective treatment method with fewer side effects and the potential for preventive application.

Our Approach: Tackling the Problem

Our innovative approach aims to genetically modify bacteria to produce a specific toxin (Cry3Aa and Cry4Ba) lethal to scabies mites while being completely harmless to humans and animals.

Initially, we will introduce the gene responsible for this toxin into Escherichia coli bacteria to test its production and effectiveness. E. coli is chosen for its well-understood genetics and ease of manipulation. Once we confirm successful toxin production, we will transfer the gene into a bacteria species naturally residing in the human skin microbiota, such as Cutibacterium acnes. This process involves inserting the gene into a plasmid, which will then be introduced into our chosen skin bacteria through a method called transformation.

Furthermore, we will incorporate RNA thermometers to trigger the toxin release by breaking down the bacterial cell wall at body temperature. RNA thermometers are temperature-sensitive RNA sequences that change their structure in response to temperature, thereby regulating gene expression. This mechanism ensures that the toxin is released directly onto the skin where the scabies mites are present, minimizing any unintended effects and maximizing the treatment's efficacy.

As a future work, a lotion will be developed containing these genetically modified bacteria. When applied to the skin, the bacteria will produce and release the selected toxin, which the scabies mites will ingest, leading to their death. This lotion aims not only to treat existing scabies infestations but also to serve as a preventive measure against potential outbreaks.

Figure 3. Innovative treatment approach utilizing genetically modified bacteria for effective scabies management.

How We Will Bring Our Solution to Life

C. acnes

Our project uses Cutibacterium acnes, a bacterium that naturally lives in the skin’s sebaceous glands. This bacterium thrives in the oily, low-oxygen environment of these glands. By leveraging this natural habitat, we can engineer it to produce treatments directly at the infection site, providing a precise and effective solution for issues like scabies. Its ability to coexist with other skin microbes without major disruption makes it ideal for synthetic biology applications.

These bacteria have been previously used by researchers at Universitat Pompeu Fabra (UPF) who have been developing innovative tools for genetic engineering of C. acnes. This has been done by implementing CRISPR interference systems, allowing the creation of functional genetic circuits, such as a NOR gate and a double-inverter cascade, enabling precise control of gene expression in C. acnes and paving the way for future therapeutic applications in skincare.

Figure 4. Schematic representation of the natural habitat where C.acnes is found.

Cry toxins

A Cry protein is a parasporal inclusion protein that exhibits toxic effects on target organisms or any protein with a clear sequence similarity to a known Cry protein. In our research, we focus specifically on Cry proteins that target scabies larvae. When ingested by insect larvae, these proteins are activated in the midgut through proteolysis. Once activated, they bind to specific receptors on the midgut epithelial cell membrane, causing intestinal perforation, halting feeding, and ultimately leading to the insect's death. These proteins are produced by Bacillus thuringiensis (Bt), a bacterium that has been proposed as an alternative biological insecticide. Unlike common chemical insecticides, which are more polluting and harmful to health, and to which insects can develop resistance, Bt-based insecticides are highly specific biological control agents. They have already been developed and used effectively for this purpose. In fact, they are much more specific than synthetic broad-spectrum insecticides, which are often limited to a single insect order. Additionally, Bt toxins do not spread or leach into non-target areas and are harmless to humans, vertebrates, and plants, being completely biodegradable. These characteristics make Bt toxins especially safe and are among the few proteins authorized for use in genetically modified organisms (GMOs), such as transgenic maize varieties developed to combat underground pests. In our laboratory, we have conducted research on the Cry3Aaa and Cry4Ba toxins, both of which are known for their specificity towards certain insect larvae. Cry3Aaa is particularly effective against coleopteran larvae, such as those responsible for scabies. This toxin's targeted action makes it a promising candidate for combating scabies infestations, as it directly attacks the larvae of the insects that cause this condition. On the other hand, Cry4Ba is specific to dipteran larvae, making it highly effective against species like flies. The distinct specificity of these toxins highlights their potential use in targeted pest control strategies, offering a more precise approach to managing insect-borne diseases.

Figure 5. Schematic representation of the mechanism of action of Cry proteins.

An overview

Our innovative approach aims to address the persistent issue of scabies through a novel treatment method utilizing genetically modified bacteria to produce Cry3Aa and Cry4Ba toxins. These toxins, produced by engineered Cutibacterium acnes, will specifically target and kill scabies mites while being harmless to humans and animals. By incorporating RNA thermometers to regulate toxin release at body temperature, we ensure localized and effective treatment. This project builds on previous research demonstrating the specificity and safety of Cry toxins, as well as advancements in genetic engineering techniques, promising a safer, more effective, and potentially preventive solution for scabies management.

Why this project?

Our team was inspired to pursue this project after extensive brainstorming sessions and consultations with our professors. Initially, we considered various ideas, such as developing a mosquito repellent or creating a solution to eliminate unpleasant street odors. However, after reflecting on current global diseases whose treatments are either non-existent or need improvement, some students in the team recalled the bothersome experience of having lice: how difficult they were to eliminate and how much they itched. The teachers, in turn, remembered the intense afternoons spent removing lice from their daughters, which led us to seek a faster, more ecological, and effective solution for both prevention and treatment. This topic led us to consider other parasitic infestations with significant socioeconomic impacts, such as scabies, a widespread condition typically treated with topical creams and, in more severe cases, oral medications. However, dermatologists warn that in recent years mites have been showing resistance to these treatments, needing a change in the therapeutic approach 5. We were motivated by the potential to help millions of people who suffer from scabies each year, providing them with a new and effective treatment option by using genetically modified bacteria to produce a targeted toxin that offered a novel and practical solution.

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