Novel Strategies for Preventing Fungal Infections Outline

1. Introduction

Fungal infections pose a substantial global burden, with recent estimates revealing approximately 6.5 million severe fungal infections occur annually, resulting in around 3.8 million fatalities, with roughly 2.5 million (68%) of these deaths directly linked to fungal diseases (Denning, 2024). Therefore, both superficial and systemic fungal infections pose significant health risks to patients, particularly those individuals that are immunocompromised (such as those with HIV/AIDS, cancer patients, organ transplant recipients, and/or those critically ill in the intensive care unit) (Aranda-Audelo et al., 2018; Hosseini et al., 2022; Elhaj Mahmoud et al., 2024; Jenks et al., 2021). Clinically relevant fungal infections can be categorized into two distinct groups: superficial and invasive. Superficial fungal infections, exemplified by thrush, oropharyngeal candidiasis, and dermatophyte infections, primarily target the skin, mucous membranes, and keratin-based tissues (Roy et al., 2023). Conversely, invasive fungal infections pose a greater threat to health, as they infiltrate and compromise normally sterile body sites, including the circulatory system, vital organs such as the lungs, liver, and kidneys, and the central nervous system (Rauseo et al., 2020). Fungal pathogens can also affect animals and plants. Thus, leading to severe agricultural losses and global economic challenges (Davies et al., 2021).

Traditionally, fungal infections have been managed with antifungal drugs such as azoles, echinocandins, and polyenes (Gintjee et al., 2020). Each of which have their own mode of action. Azoles disrupt fungal cell membrane integrity by inhibiting the demethylation of lanosterol through CYP51 enzymatic activity. This, in turn, prevents the formation of ergosterol, which is a vital sterol in the structure and function of the cell membrane. Polyenes, on the other hand, specifically target ergosterol in the fungal membranes, compromising their structural integrity, and leading to cell lysis. Conversely, echinocandins inhibit the synthesis of β-glucan, a vital polysaccharide component of the fungal cell wall, thereby hindering cell wall formation (Nahar et al., 2024). Despite the mechanisms of all these antifungal agents, fungi are becoming more resistant to them leading fungal infections to be a serious threat to global health (Hokken et al., 2019).

The primary drivers of antifungal resistance include the overuse and misuse of antifungal agents, such as azoles and echinocandins, in both the medical and agricultural sectors (Fisher et al., 2018). In particular, the widespread use of azoles in crop protection has been linked to cross-resistance in clinical settings, as certain fungal pathogens develop resistance to treatments used in both domains (Kaur et al., 2020). Aspergillus spp. is notorious for developing resistance. For instance, Aspergillus fumigatus has demonstrated increasing resistance to azoles, partly due to mutations in the target enzyme CYP51A, which is essential for the production of ergosterol (Hsu et al., 2022). This is not solely related to Aspergillus spp. In the case of Candida auris, multidrug resistance has become a significant global concern. C. auris can withstand multiple classes of antifungals, including azoles and polyenes, making treatment of infections extremely challenging (Mirabet et al., 2021).

The clinical implications of antifungal resistance are profound, leading to higher morbidity, mortality, and treatment costs (Cui et al., 2022). Strategies to combat resistance include the development of new antifungal agents, combination therapies, and improved stewardship programs to regulate antifungal usage (Nahar et al., 2024). However, the pace of drug development lags behind the emergence of resistant strains, necessitating more robust research and policy efforts to mitigate this growing threat (Fisher et al., 2018). More so, the similarity in cellular structure between fungi and humans poses a major obstacle in antifungal drug development, necessitating a meticulous search for selective inhibitors that spare human cells, which is both time-consuming and financially burdensome (van Rhijn et al., 2024).

In addition, the potential of antifungal agents to cause adverse effects often limits their use in medical practice, particularly in immunocompromised patients (Campoy & Adrio, 2017). For example, polyenes, like amphotericin B, are highly effective broad-spectrum antifungal agents, but their nephrotoxicity is a major concern. Amphotericin B can cause renal impairment by binding to cholesterol in mammalian cell membranes, leading to cell damage (Perazella & Shirali, 2014). Lipid formulations of amphotericin B have been developed to reduce renal toxicity, but these are more expensive (Faustino & Pinheiro, 2020) and still present some risk of kidney damage (Moghnieh et al., 2016). Azole antifungals, such as fluconazole and itraconazole, are widely used due to their broad activity and oral bioavailability. However, they can lead to hepatotoxicity, particularly in prolonged treatments (Rakhshan et al., 2023). Azoles inhibit cytochrome P450 enzymes, which can result in the accumulation of toxic metabolites in the liver (Rakhshan et al., 2023). The incidence of antifungal drug-induced liver injury varies, with voriconazole, fluconazole, and itraconazole accounting for the highest rates at 32.45%, 19.37%, and 14.51%, respectively (Zhou et al., 2022). Echinocandins, like caspofungin and micafungin, are generally well-tolerated but can cause mild to moderate liver toxicity and gastrointestinal disturbances (Nett & Andes, 2016). Compared to azoles and polyenes, echinocandins demonstrate improved tolerability and reduced harmful side effects, although hypersensitivity and cardiac issues remain potential concerns (Zhu et al., 2023).

The rising incidence of antifungal resistance, limited treatment options, and the toxicity of existing antifungals (Hossain et al., 2022) have necessitated the exploration of novel fungal preventive strategies. Recent advances in biotechnology, immunology, and nanotechnology have led to the development of innovative approaches such as vaccines, antifungal peptides, nanoparticles, probiotics, immunotherapy, and omics technologies (Croitoru et al., 2024; Mobeen et al., 2022; Wijayawardene et al., 2023). These strategies offer potential breakthroughs in the prevention of fungal infections, promising to overcome the limitations of conventional treatments. Therefore, this review aims to explore novel strategies for preventing fungal infections and it will focus on vaccines, antifungal peptides, nanoparticles, probiotics, immunotherapy, and omics technologies.

2. The Role of Vaccines in Preventing Fungal Infections

Vaccination is one of the most effective methods for preventing infectious diseases (Hussain, 2019). However, developing vaccines for fungal infections has proven more challenging than for bacterial or viral pathogens due to the complexity of fungal cell structures (Da Silva et al., 2020) and the immune evasion strategies they employ by covering β-1,3-glucan and chitin with different molecules (Hernández-Chávez et al., 2017). Effective vaccination against invasive fungal infections relies on inducing robust cell-mediated immunity, characterized by Th1 and Th17 responses. This enhances the host’s phagocytic capabilities, leading to improved fungal clearance. The search for suitable vaccine antigens extends beyond virulence factors, opening up a vast array of potential targets for investigation (Scorzoni et al., 2017).

Developing effective fungal vaccines face numerous hurdles due to diverse host vulnerabilities and varied mechanisms of fungal infection. A universal fungal vaccine is unlikely, as no single antigen can provide broad protection. Instead, targeted vaccine strategies will be necessary for each major fungal pathogen, accounting for unique host-fungus interactions and pathogenic processes (Tesfahuneygn & Gebreegziabher, 2018). The challenges of being unable to develop a universal fungal vaccine might not be unconnected to the fact that diverse antigens have been adopted in the creation of different fungal vaccines. However, it has been reported that the conservation of specific compounds within fungal cell walls and plasma membranes presents an opportunity for developing a broadly protective vaccine. Shared antigens among diverse fungal pathogens could potentially serve as a common target, enabling protection against various mycoses and possibly even diseases caused by distinct microorganisms (Hamad, 2012). For instance, a conjugate vaccine combining β-1,3-glucan with diphtheria toxoid has demonstrated efficacy against a range of fungal pathogens, conferring dual protection against aspergillosis and candidiasis (Pattison et al., 2021).

In addition, vaccines targeting Candida, Aspergillus, and Cryptococcus species, which are among the most common causes of invasive fungal infections, are currently under development (Oliveira et al., 2021). One promising approach involves the use of recombinant protein-based vaccines. These vaccines, which contain specific fungal antigens, stimulate the immune system to recognize and attack the fungal pathogen. For example, NDV-3A, a vaccine targeting C. albicans and Staphylococcus aureus (a bacterium which is the causal agent of a variety of skin infections, respiratory infections, and food poisoning), has shown promising results in preclinical studies and early-phase clinical trials (Edwards et al., 2018). Another promising candidate is the Cryptococcus neoformans vaccine, which has shown efficacy in animal models (Normile et al., 2022) and may soon be evaluated for human use. Although fungal vaccines are not yet widely available, these advances represent a significant step toward preventing fungal infections in high-risk populations. Also, researchers are actively exploring alternative targets, such as Als3p, a key component of Candida albicans’ cell wall, with encouraging preliminary results (Singh et al., 2022). These innovative approaches pave the way for developing more efficacious fungal vaccines.

3. Antifungal Peptides: A Novel Class of Antifungal Agents

Antifungal peptides (AFPs) are short chains of amino acids that possess broad-spectrum antifungal activity (Song et al., 2024). These peptides, often derived from natural sources such as plants, animals, and microorganisms, have garnered attention due to their ability to disrupt fungal cell membranes and inhibit fungal growth (Ul Haq et al., 2024; Brady et al., 2019). AFPs represent a novel class of antifungal agents that could complement or replace traditional antifungal drugs, especially in the context of increasing drug resistance (Song et al., 2024). The rapid evolution and adaptability of fungi pose significant challenges to antifungal treatments. However, AFPs target cell membranes, which evolve more slowly, rendering them effective against fungal pathogens (Fernández de Ullivarri et al., 2020). This multifaceted mechanism minimizes the risk of resistance emergence in target pathogens (Yeung et al., 2011). However, prudent AFP usage is crucial to prevent accelerated resistance development, as observed with conventional antimicrobials (Fernández de Ullivarri et al., 2020).

Nonetheless, AFPs offer several advantages over conventional antifungal agents, stemming from their distinctive modes of action and molecular specificity. Their capacity to bind multiple microbial targets reduces the potential for resistance development (Rautenbach et al., 2016). AFPs also exhibit low cytotoxicity due to their specific interaction with conserved fungal targets, such as glucosylceramide and enzymes essential for ergosterol biosynthesis. This selective binding reduces harm to mammalian cells (Rautenbach et al., 2016). AFPs have a complex role in therapy, with Host Defense Peptides (HDPs), such as defensins and cathelicidins, demonstrating angiogenic, immunomodulatory, and anti-inflammatory properties, in addition to recruiting adaptive immune cells, thereby exhibiting multifaceted therapeutic profile (Hsieh & Hartshorn, 2016; Li et al., 2017).

Several AFPs have demonstrated potent antifungal activity against various fungal pathogens. For example, defensins, a family of peptides produced by plants and animals, exhibit antifungal properties by disrupting fungal cell walls and inhibiting spore germination (Sathoff et al., 2019). Another promising group of AFPs includes histatins, salivary peptides that have shown activity against C. albicans (Zolinet al., 2021). Also, cathelicidin such as LL-37 exhibits potent anti-adhesive activity against C. albicans in a murine urinary tract model, resulting in a substantial reduction (over 70%) in yeast attachment to bladder tissue (Song et al., 2022). These peptides offer a potential alternative to conventional antifungals, with the added benefits of low toxicity and reduced risk of developing resistance.

Although AFPs hold promise for combating infections resistant to conventional treatments, but a critical knowledge gap persists regarding the interplay between their molecular structure and biological activity, thereby impeding accelerated translation into therapeutic applications (Song et al., 2024). This explains why to date, only a small number of antifungal peptides have entered clinical trials, including nikkomycin Z, aureobasidin A, and VL-2397, which hold significant promise for addressing the urgent need for novel antifungal treatments (Rauseo et al., 2020). Nevertheless, a coordinated approach among stakeholders – regulatory bodies, researchers, and industry leaders – is crucial for accelerating the development of peptide-based antifungal solutions. Peptides’ potent antifungal activity, stability across various temperatures and pH levels, and resistance to proteolysis make them attractive candidates for clinical therapeutics, warranting further investigation and collaboration (Scarsini et al., 2015; Ul Haq et al., 2024).

4. Nanoparticles and Nanotechnology-Based Therapies

Current treatments for systemic fungal infections face significant challenges due to existing antifungals’ inadequate distribution, efficacy, and specificity, as well as their potential for severe adverse effects (Voltan et al., 2016). However, nanotechnology offers a promising solution, enabling the development of targeted and controlled drug delivery systems through nanoparticles (NPs). This innovative approach can enhance the effectiveness of fungal infection treatments while minimizing harm to patients’ overall well-being (Kischkel et al., 2020). Thus, nanotechnology-based therapies are gaining attention for their potential to revolutionize the prevention and treatment of fungal infections (Asghari-Paskiabi & Jahanshiri, 2024). Various studies have shown that nanoparticles exhibit reduced side effects, enhanced targeting of infection sites, do not lead to drug resistance, improve the stability and solubility of antifungal agents, and boost overall effectiveness (Bhatt et al., 2018; Escárcega-González et al., 2018; Sousa et al., 2020). Moreover, nanoparticles can be tailored with precise surface modifications, enabling selective recognition and binding to diseased cells, thereby enhancing therapeutic precision, minimizing harm to healthy cells, and optimizing drug performance (Huang et al., 2010).

Various types of nanoparticles have been explored for antifungal purposes, including liposomes, metallic nanoparticles, and polymeric nanoparticles. Liposomal formulations, such as liposomal amphotericin B, have already been approved for clinical use and have demonstrated enhanced efficacy and reduced toxicity compared to conventional amphotericin B (Hamill, 2013). Metallic nanoparticles, such as silver and gold nanoparticles, have also shown promise due to their antifungal properties and ability to disrupt fungal biofilms (Hashem et al., 2022; Miškovská et al., 2022). A study demonstrated that the enhanced antifungal efficacy of biosynthesized silver nanoparticles (AgNPs) stabilized with sodium dodecyl sulfate (SDS) and reduced using ribose, has significant inhibitory effects against Candida albicans and Candida tropicalis (Mallmann et al., 2015). In addition, Fajar et al. (2019) have shown that AgNPs inhibit Aspergillus niger growth by up to 70% and suppress Cladosporium cladosporoides growth by up to 90%. The antifungal activity of AgNPs exhibits a dose-dependent relationship, with increased concentrations minimizing fungal growth.

Silver nanoparticles have been found to exhibit significant antifungal properties against A. niger. They achieve this by preventing spore germination and biofilm formation. When combined with simvastatin, a statin that disrupts fungal cell membrane integrity, the antifungal effect is enhanced. This synergy is likely due to the increased susceptibility of fungal cells to nanoparticle entry (Bocate et al., 2019). Silver nanoparticles have shown potent antifungal activity against Trichophyton mentagrophytes clinical isolates and C. albicans (Zhang et al., 2016). Nanotechnology-based strategies not only provide more effective drug delivery systems, but also offer new avenues for developing antifungal therapies that could prevent infection at early stages (Guo & He, 2024). Despite the promise of emerging therapies, significant uncertainties surround their effectiveness and safety in humans. Some studies lack rigorous clinical trials, and practical limitations, such as cumbersome administration methods or high production costs, may impede their adoption as viable alternatives to established treatments (El Meshad & Mohsen, 2016; Maheshwari et al., 2012; Ning et al., 2005).

5. Probiotics and Their Role in Fungal Infection Prevention

Probiotics, which are live microorganisms that confer health benefits when consumed in sufficient amounts, have gained popularity for their role in maintaining a balanced microbiota and preventing infections (Maftei et al., 2024). While probiotics are commonly associated with bacterial infections, recent studies have demonstrated their potential in preventing fungal infections, particularly those caused by Candida species (Ang et al., 2022; Davar et al., 2016; Russo et al., 2019). Research suggests that probiotics, when used as adjunctive treatment, may enhance short-term outcomes for fungal infections, leading to improved clinical and mycological resolution rates and reduced relapse rates within a one-month period, however, their effectiveness as a long-term solution remains uncertain (Xie et al., 2017).

Studies have shown that probiotics offer protective benefits against fungal infections, particularly vulvovaginal candidiasis (VVC). Both oral and vaginal probiotic administration can significantly alleviate symptoms of discharge and itching/irritation (Mändar et al., 2023). Furthermore, probiotics have been shown to substantially reduce VVC recurrence rates compared to placebo, with notable differences observed over extended follow-up periods (Davar et al., 2016; Russo et al., 2019). Notably, probiotic-treated individuals exhibited improved symptom management and reduced recurrence rates at both 3- and 6-month follow-ups, underscoring the potential of Lactobacilli-based mixtures as a safe and effective adjunctive therapy for managing recurrent VVC (Russo et al., 2019). Probiotics have been found to exhibit strong anti-biofilm properties during early fungal biofilm formation. However, their inhibitory effects are substantially reduced against biofilms in later stages of growth (Kean and Ramage, 2019; Matsubara et al., 2016). Therefore, more research is needed to fully understand the mechanisms underlying probiotic-mediated fungal inhibition, because probiotics represent a promising, natural strategy for preventing fungal infections, particularly in immunocompromised individuals.

Inconsistent results from several studies have sparked controversy regarding the efficacy of probiotics in addressing VVC, potentially attributed to variations in strain specificity, administration methods, and treatment regimens (van de Wijgert & Verwijs, 2020; Tsimaris et al., 2019). It has been argued that the effectiveness of probiotics in managing VVC varies, and it depends on the patient’s specific condition, whether it is an acute episode, recurrent infection, or heightened susceptibility to infection (Shenoy and Gottlieb, 2019).

6. Immunotherapy: Harnessing the Immune System to Combat Fungal Infections

Immunotherapy, which involves modulating the immune system to enhance its ability to fight infections, has emerged as a novel approach for preventing fungal infections (Abate, 2023). Fungal pathogens can evade the immune system by masking their antigens or suppressing immune responses, making it challenging for the body to mount an effective defence (Hernández-Chávez, 2017). Immunotherapy aims to overcome these challenges by boosting the immune system’s capacity to recognize and eliminate fungal pathogens (Posch et al., 2020). Immunity against fungal infections primarily relies on the activation of cellular immune responses, mediated by CD4⁺ T helper cells. Specifically, Th1 and Th17 responses trigger the release of pro-inflammatory cytokines, including IL-12, IL-17A, IFN-γ, GM-CSF, and TNF-α, which mobilize various immune cells such as neutrophils, macrophages, and dendritic cells (Parente-Rocha et al., 2017). Conversely, fungal infection progression is associated with a shift from Th1-type responses to Th2-mediated responses, characterized by CD4⁺ T-helper cells producing cytokines like IL-4, IL-5, and IL-10 (Taborda & Nosanchuk, 2017).

Several immunotherapeutic strategies are currently being explored for fungal infection prevention and preclinical studies have consistently demonstrated that cytokines significantly strengthen the immune system’s ability to combat fungal infections, largely by optimizing the performance of phagocytic cells. Extensive research in both human and murine models has unequivocally demonstrated that IL-17 plays a crucial and remarkably specialized role in safeguarding against C. albicans (Davidson et al., 2018). Although IL-2 and IL-12 have shown promise therapeutically, their clinical utility is limited due to systemic toxicity issues. In contrast, IL-23, a cytokine closely related to IL-12, has emerged as a key player in the immune response to chronic fungal infections (Segal et al., 2006).

Another approach involves the use of immune checkpoint inhibitors, which block inhibitory signals that dampen the immune response, thereby enhancing the activity of immune cells against fungal pathogens (Wurster et al., 2022). Another strategy is adoptive T-cell therapy, which involves transferring T-cells from a healthy donor to an immunocompromised patient to boost their immune defence against fungal infections (Sharma et al., 2022). In the context of fungal immunity, T cells play a dual role as modulators and effectors. The Th1 response, initiated by TLR4 signalling, drives the production of IFN-γ and TNF-α, essential for fungal pathogen clearance. In contrast, TLR2-mediated Th2 responses generate anti-inflammatory cytokines, including IL-4 and IL-10, which regulate inflammation but compromise fungal resistance. Recently, Th17 cells have gained recognition for their crucial involvement in mucosal immunity against Candida (Ravikumar et al., 2015). Although these therapies are still in experimental stages, they hold great promise for preventing fungal infections, especially in individuals with weakened immune systems.

7. Omics Technologies for Fungal Infection Prevention

The advent of omics technologies, such as genomics, proteomics, and metabolomics, has revolutionized our understanding of fungal biology and opened new possibilities for preventing fungal infections (Hyde et al., 2024; Wijayawardene et. al., 2023). These technologies enable researchers to study fungal pathogens at the molecular level, identifying potential targets for new antifungal therapies and vaccines (Ball et al., 2020). For example, genomics has provided valuable insights into the genetic makeup of fungal pathogens, allowing for the identification of virulence factors and drug resistance genes (Al Jindan et al., 2022). Proteomics has facilitated the discovery of fungal proteins involved in host-pathogen interactions, which could serve as targets for vaccine development or therapeutic interventions (Champer et al., 2016). Additionally, metabolomics has shed light on the metabolic pathways that fungi rely on for survival, offering potential targets for novel antifungal drugs (Li et al., 2022). By integrating omics data, researchers can develop more effective strategies for preventing fungal infections and overcoming the challenges posed by drug-resistant pathogens.

A comprehensive metabolomic analysis of antifungal resistance in C. albicans was conducted using a combination of cutting-edge mass spectrometry techniques, including ultrahigh-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF/MS) and hydrophilic interaction liquid chromatography-mass spectrometry (HILIC-MS) for targeted phospholipid metabolism. This integrated approach revealed a wide array of metabolite biomarkers associated with drug stress response and resistance mechanisms, highlighting alterations in amino acid, sphingolipid, and phospholipid metabolic pathways (Subramanian et al., 2020). In addition, the integration of transcriptomics and epigenomics has significantly enhanced the comprehension of complex cellular dynamics. A growing body of evidence indicates that immune cells exhibit metabolic adaptability, tailoring their responses to meet distinct defensive needs through the coordinated action of epigenetic regulators and metabolic networks (Chen et al., 2014; Saeed et al., 2014).

Recent research has leveraged omics technologies to elucidate specific immune responses elicited by fungal infections. For example, de Jesús-Gil et al. (2021) discovered that C. albicans triggers IL-17-mediated immunity, particularly in psoriasis patients, highlighting the critical role of IL-17 in inflammatory processes. This finding has significant implications for identifying therapeutic targets. Conversely, Stuehler et al. (2015) investigated Th1-mediated immunity against A. fumigatus antigens, a fungus notorious for causing respiratory infections in immunocompromised individuals. The ability to pinpoint these precise immune reactions is vital for developing tailored and effective treatments.

The integration of cutting-edge omics technologies, including genomics, transcriptomics, proteomics, and metabolomics, provides a holistic understanding of the complex interactions between fungi and the immune system (Wijayawardene et al., 2023). By leveraging these approaches, researchers can identify novel fungal antigens and immune targets, paving the way for the development of innovative vaccines and immunotherapies (Leitão & Rodríguez-Ortega, 2020). Furthermore, these insights can inform the design of adoptive T-cell transfer therapies, which involve genetically modifying immune cells to enhance their antifungal efficacy, offering new hope for combating fungal infections (Hudson & Wieland, 2023).

Despite the prospect of Omics technologies, its adoption in fungal prevention faces several challenges. One key issue is the complexity of fungal genomes, which makes data interpretation difficult. High-throughput techniques like genomics, proteomics, and metabolomics generate vast amounts of data that require advanced bioinformatics tools for analysis, creating a barrier for widespread use (Wijayawardene et al., 2023; Hyde et al., 2024). Additionally, the cost of implementing omics technologies is high, limiting access for many researchers, particularly in low-resource settings (Dai & Shen, 2022). Ethical concerns regarding data privacy and the need for standardization across platforms also hinder progress (Bianconi et al., 2023).

8. Conclusion

The rise in antifungal resistance and the prevalence of fungal infections underscore the urgent need for innovative approaches for prevention and treatment. Whilst conventional antifungal therapies can be effective, we are observing increasing issues in resistance, toxicity, and limited therapeutic options, particularly in immunocompromised patients. This underlines the need for a multifaceted strategy that integrates novel preventive measures and therapeutic interventions.

Advanced approaches such as vaccines, antifungal peptides, nanotechnology, probiotics, immunotherapy, and omics technologies offer promising pathways to address these challenges. Each strategy brings unique advantages and challenges. Addressing these challenges will require collaborative efforts among researchers, healthcare professionals, regulatory authorities, and industry stakeholders. By leveraging cutting-edge innovations alongside traditional therapies, we can improve outcomes for patients and mitigate the growing threat of fungal infections to global health.