Relevant Animal Models in Dermatophyte Research

Global, regional, and national burden of fungal skin diseases in 204 countries and territories from 1990 to 2021: An analysis of the global burden of disease study 2021

BACKGROUND

Fungal skin diseases are common skin diseases with a heterogeneous distribution worldwide.

OBJECTIVES

This study aimed to analyse the spatiotemporal trends in the burden of fungal skin diseases at global, regional, and national levels from 1990 to 2021.

METHODS

Based on the data obtained from the Global Burden of Disease Study (GBD) 2021, we described the incident cases, prevalent cases, number of disability-adjusted life years (DALYs), and corresponding age-standardised rates (ASRs) for fungal skin diseases in 1990 and 2021 by sex, age, socio-demographic index (SDI), 21 GBD regions, and 204 countries and territories. We used Joinpoint regression analysis to assess the temporal trends in burden of fungal skin diseases during 1990 to 2021. Spearman's rank test was used to analyse the relationship between disease burden and potential factors.

RESULTS

From 1990 to 2021, the incident cases, prevalent cases, and DALYs for fungal skin diseases worldwide increased by 67.93%, 67.73%, and 66.77%, respectively. Globally, the age-standardised incidence rate (ASIR), age-standardised prevalence rate (ASPR), and age-standardised DALYs rate (ASDR) for fungal skin diseases in 2021 were 21668.40 per 100,000 population (95% UI: 19601.19-23729.17), 7789.55 per 100,000 population (95% UI: 7059.28-8583.54), and 43.39 per 100,000 population (95% UI: 17.79-89.10), respectively. Between 1990 and 2021, the ASIR, ASPR, and ASDR for fungal skin diseases have modestly increased, with AAPC of 11.71% (95% confidence interval [CI]: 11.03%-12.39%), 19.24% (95% CI: 18.12%-20.36%), and 20.25% (95% CI: 19.33%-21.18%), respectively. Males experienced a higher burden of fungal skin diseases than females. The incident cases, prevalent cases, and DALYs for fungal skin diseases were highest at the age of 5-9, while the ASRs were highest among the elderly. At national level, the highest ASRs were observed in Nigeria, Ethiopia, and Mali. Overall, SDI was negatively correlated with the ASRs, whereas Global Land-Ocean Temperature Index (GLOTI) was remarkably positively correlated with the burden of fungal skin diseases.

CONCLUSIONS

Between 1990 and 2021, the global burden of fungal skin diseases has increased, causing a high disease burden worldwide, particularly in underdeveloped regions and among vulnerable population such as children and the elderly. With global warming and aging of the population, the burden of fungal skin diseases may continue to increase in the future. Targeted and specific measures should be taken to address these disparities and the ongoing burden of fungal skin diseases.

Antifungal activity of aminopyrrolnitrin against Trichophyton verrucosum in a guinea pig model of dermatophytosis

BACKGROUND

Dermatophytosis is a common and major public health concern worldwide. Despite the increasing availability of antifungal drugs, relapses and untreated cases of dermatophyte infections are reported. Therefore, novel antifungal agents are required. Aminopyrrolnitrin (APRN) shows promise for dermatophytosis treatment because of its antifungal activity.

OBJECTIVES

This study aimed to assess the antifungal properties of APRN against Trichophyton verrucosum (T. verrucosum), in both laboratory settings and a guinea pig model.

METHODS

The minimum inhibitory concentrations (MICs) of APRN and enilconazole against T. verrucosum were determined according to the CLSI M38 method. The skins of 16 male guinea pigs were infected with 1.0 × 108 conidia of T. verrucosum and the animals were grouped into sets of four: negative control group (NC) received normal saline; positive control group (PC) received 2 μg/mL of enilconazole; and APRN4 and APRN8 received 4 and 8 μg/mL of APRN, respectively. Clinical, mycological and histological efficacies were measured after 10 days.

RESULTS

The MIC90 of APRN and enilconazole against T. verrucosum was 4 and 2 μg/mL, respectively. The clinical scores of PC, APRN4, and APRN8 were significantly lower than those of NC. Clinical and mycological efficacies were higher for APRN8, APRN4 and PC. No fungi were observed in the skin tissues of APRN4 and APRN8, while fungi were observed in 50% of the PC.

CONCLUSION

APRN showed antifungal activity against T. verrucosum in vitro and in vivo and is a potential candidate for the treatment of dermatophytosis.

In vitro and In vivo study targeting the development of Unani Antidermatophytic Cream: Implication of Herbal Formulations in Treatment of Dermatophytosis

Panwad (Cassia tora L.), Sarshaf (Brassica nigra L.) and Kunjad (Sesamum indicum L.) have been used in the treatment of ringworm infection since ancient times and are documented in classical literature of Unani Medicine. These plant drugs give promising results when used topically in the form of paste (zimad). Hence, the development and evaluation of a cream containing extracts of Tukhm-e-Panwad (Cassia tora L.), Sarshaf (Brassica nigra L.), and Kunjad (Sesamum indicum L.) was carried out to get better efficacy of the drugs. A total of 16 batches (F1-F16) of cream were prepared by adding varying concentrations of hydro-alcoholic extract of the drugs (20%, 40% and 50%) in water removable bases, and three batches were selected as final batches (F4-20%, F6-40% and F16-50%). In vitro antidermatophytic activity was conducted to optimize MIC against dermatophytosis-causing fungi. Dermal irritation of the prepared cream was determined in New Zealand Albino Rabbits. In vivo testing of the different concentrations of the prepared cream (20%, 40%, and 50%) was also carried out using Wistar rats to assess the antidermatophytic activity. Final batches showed good results in all the tested parameters and significant in vitro and in vivo antifungal activity in a dose-dependent manner. No microbial growth was seen in the prepared formulation. The study revealed significant antidermatophytic activity of the prepared cream against dermatophytosis-causing fungi. Hence, it can be concluded that the prepared cream can be an alternative topical agent with safe and effective antifungal activity for treating dermatophytosis.

Microsporum gypseum Isolated from Ailuropoda melanoleuca Provokes Inflammation and Triggers Th17 Adaptive Immunity Response

Microsporum gypseum causes dermatomycoses in giant pandas (Ailuropoda melanoleuca). This study aimed to investigate the immune response of M. gypseum following deep infection. The degree of damage to the heart, liver, spleen, lungs, and kidneys was evaluated using tissue fungal load, organ index, and histopathological methods. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) detected the mRNA expression of receptors and cytokines in the lung, and immunofluorescence staining and flow cytometry, were used to assess immune cells in the lung. The results indicated that conidia mainly colonized the lungs and caused serious injury with M. gypseum infection. Furthermore, dectin-1, TLR-2, and TLR-4 played a role in recognizing M. gypseum cells. Numerous inflammatory cells, mainly macrophages, dendritic cells, polymorphonuclear neutrophils, and inflammatory cytokines (TGF-β, TNF-α, IL-1β, IL-6, IL-10, IL-12, and IL-23), were activated in the early stages of infection. With the high expression of IL-22, IL-17A, and IL-17F, the Th17 pathway exerted an adaptive immune response to M. gypseum infection. These results can potentially aid in the diagnosis and treatment of diseases caused by M. gypseum in giant pandas.

Evaluation of Topical Antifungals Using a New Predictive Animal Model for Efficacy against Severe Tinea Unguium: A Comparison of Efinaconazole and Luliconazole

Development of new topical drugs requires an animal onychomycosis model that can predict the drug efficacy against moderate to severe human onychomycosis because the severity of onychomycosis varies and affects the drug efficacy. This study established a non-immunosuppressive guinea pig tinea unguium model under 8-week infection condition in addition to a previously reported model under 4-week infection condition. In the tinea unguium model, most fungi were tightly present in the arthrospore form, like in human onychomycosis. The topical formulations of efinaconazole and luliconazole, two azole class anti-onychomycosis drugs, were evaluated for their efficacy in these models. In the untreated group, the nail fungal burden in the 8-week model was higher than that in the 4-week model and the stronger infection intensity affected the efficacy of the drugs, suggesting that the 8-week model was more severe. The 90% efficacy rate (42%) of luliconazole in the 8-week model was significantly lowered than that (83%) in the 4-week model, and its 99% efficacy rates were 0% in both models. Conversely, the 90% and 99% efficacy rates of efinaconazole (92% and 50% in the 4-week model, and 75% and 25% in the 8-week model, respectively) were not significantly different between the two infection durations. In addition, efinaconazole was more effective than luliconazole in reducing the nail fungal burden. Considering the relevance of clinical reports of the effectiveness of efinaconazole on severe onychomycosis, the new severe tinea unguium model would predict drug efficacy against moderate to severe onychomycosis.

Towards a Standardized Procedure for the Production of Infective Spores to Study the Pathogenesis of Dermatophytosis

Dermatophytoses are superficial infections of human and animal keratinized tissues caused by filamentous fungi named dermatophytes. Because of a high and increasing incidence, as well as the emergence of antifungal resistance, a better understanding of mechanisms involved in adhesion and invasion by dermatophytes is required for the further development of new therapeutic strategies. In the last years, several in vitro and in vivo models have emerged to study dermatophytosis pathogenesis. However, the procedures used for the growth of fungi are quite different, leading to a highly variable composition of inoculum for these models (microconidia, arthroconidia, hyphae), thus rendering difficult the global interpretation of observations. We hereby optimized growth conditions, including medium, temperature, atmosphere, and duration of culture, to improve the sporulation and viability and to favour the production of arthroconidia of several dermatophyte species, including Trichophyton rubrum and Trichophyton benhamiae. The resulting suspensions were then used as inoculum to infect reconstructed human epidermis in order to validate their ability to adhere to and to invade host tissues. By this way, this paper provides recommendations for dermatophytes culture and paves the way towards a standardized procedure for the production of infective spores usable in in vitro and in vivo experimental models.

Olorofim Effectively Eradicates Dermatophytes In Vitro and In Vivo

Superficial fungal infections are prevalent worldwide, with dermatophytes as the most common cause. Various antifungal agents including azoles and allylamines are commonly used to treat dermatophytosis. However, their overuse has yielded drug-resistant strains, calling for the development of novel antimycotic compounds. Olorofim is a newly developed antifungal compound that targets pyrimidine biosynthesis in molds. The purpose of this study was to determine the in vitro and in vivo antifungal effects of olorofim against common dermatophytes. The in vitro activity of olorofim against dermatophytes was assessed by microtiter broth dilution method. Bioinformatic analysis of olorofim binding to dihydroorotate dehydrogenase (DHODH) of dermatophytes was also performed, using Aspergillus fumigatus DHODH as a template. The in vivo efficacy of the drug was investigated, using a guinea pig model, experimentally infected with Microsporum gypseum. Microtiter assays confirmed the high in vitro sensitivity of dermatophytes to olorofim (MIC = 0.015-0.06 mg/liter). Amino acid sequence analysis indicated that DHODH is highly conserved among dermatophytes. The critical residues, in dermatophytes, involved in olorofim binding were similar to their counterparts in A. fumigatus DHODH, which explains their susceptibility to olorofim. Typical skin lesions of dermatophyte infection were observed in the guinea pig model at 7 days postinoculation. Following 1 week of daily topical administration of olorofim, similar to the clotrimazole group, the skin lesions were resolved and normal hair growth patterns appeared. In light of the in vitro and in vivo activity of olorofim against dermatophytes, this novel agent may be considered as a treatment of choice against dermatophytosis.

Nanoencapsulated hypericin in P-123 associated with photodynamic therapy for the treatment of dermatophytosis

The antifungal application of photodynamic therapy (PDT) has been widely explored. According to superficial nature of tinea capitis and the facility of application of light sources, the use of nanoencapsulated hypericin in P-123 associated with PDT (P123-Hy-PDT) has been a poweful tool to treat this pathology. Thus, the aim of this study was to evaluate the efficiency of P123-Hy-PDT against planktonic cells and in a murine model of dermatophytosis caused by Microsporum canis. In vitro antifungal susceptibility and in vivo efficiency tests were performed, including a skin toxicity assay, analysis of clinical signs by evaluating score, and photoacoustic spectroscopy. In addition, tissue analyses by histopathology and levels of pro-inflammatory cytokines, such as quantitative and qualitative antifungal assays, were employed. The in vitro assays demonstrated antifungal susceptibility with 6.25 and 12.5 μmol/L P123-Hy-PDI; these experiments are the first that have used this treatment of animals. P123-Hyp-mediated PDT showed neither skin nor biochemical alteration in vivo; it was safe for dermatophytosis treatment. Additionally, the treatment revealed rapid improvement in clinical signs at the site of infection after only three treatment sessions, with a clinical score confirmed by photoacoustic spectroscopy. The mycological reduction occurred after six treatment sessions, with a statistically significant decrease compared with untreated infected animals. These findings showed that P123-Hy-PDT restored tissue damage caused by infection, a phenomenon confirmed by histopathological analysis and proinflammatory cytokine levels. Our results reveal for the first time that P123-Hy-PDT is a promising treatment for tinea capitis and tinea corporis caused by M. canis, because it showed rapid clinical improvement and mycological reduction without causing toxicity.

Facilitating Drug Discovery in Human Disease Models Using Insects

Drugs are developed through basic studies and clinical trials. In basic studies, researchers seek drug candidates using in vitro evaluation systems and subsequently examine their effectiveness in animal experiments as in vivo evaluations. Drug candidates identified in basic studies are tested to determine whether they are effective against human diseases in clinical trials. However, most drug candidates identified in in vitro evaluation systems do not show therapeutic effects in animal experiments due to pharmacokinetics and toxicity problems in the in vivo evaluations. This review outlines drug discovery using insect disease models that allow us to perform in vivo screening. Since insects have various advantages as experimental animals such as low cost for rearing and few ethical concerns, researchers can perform large-scale in vivo screening to find drug candidates. Silkworms are insects frequently used for studies of drug efficacy, pharmacokinetics, and toxicity. Based on silkworm research, I describe the benefits of using insect disease models for drug discovery. The use of insect disease models for in vivo screening is expected to facilitate drug discovery.

In vitro models of dermatophyte infection to investigate epidermal barrier alterations

Fungal infections of the skin, known as dermatophytoses, are initiated at the epidermal barrier and lead to dysfunctions of the stratum corneum and cornified skin appendages. Dermatophytosis affects a significant part of the human population and, despite the availability of effective treatments, its prevalence is still increasing. Numerous dermatophyte species are able to induce lesions in both animals and humans, with different clinical pictures and host inflammatory responses. The understanding of the infectious process and of tissue responses has been impeded by discrepancies between observations in vivo or in research models. Indeed, cells cultured as monolayers do not undergo the keratinization process required to study the adherence and invasion of dermatophytes. Animal models lack relevance to study human dermatophytosis because of species-specific differences in the development of lesions and inflammatory responses. This review focuses on the recent development of cultured human skin equivalents, which partly overcomes those limitations and allows improved understanding of the pathogenesis of dermatophytosis in human being, especially the impacts of infection on epidermal barrier integrity.

Silkworm as an experimental animal for research on fungal infections

Silkworm, Bombyx mori, has various advantages as an experimental animal, such as the low cost for rearing and fewer ethical problems. Models utilizing silkworms of infection with pathogenic bacteria have been established for identification of genes encoding virulence factors by large-scale in vivo screening. In this review, we describe recent progress in the study of silkworm infection models for elucidating the mechanisms of fungi infection. Silkworm infection models have been established for Candida albicans, Candida tropicalis, Candida glabrata and Cryptococcus neoformans, which are yeast type fungi, and Aspergillus fumigatus, Arthroderma vanbreuseghemii, Arthroderma benhamiae, Microsporum canis, Trichophyton rubrum, and Rhizopus oryzae, which are filamentous fungi. Novel genes encoding virulence factors in C. albicans and C. glabrata have been identified by using the silkworm infection models. We here outline the benefits of using silkworm infection models and a strategy for identifying the genes responsible for pathogenicity of microorganisms such as fungi. © 2019 The Authors. Microbiology and Immunology Published by The Societies and John Wiley & Sons Australia, Ltd.

Fungal infections in animals: a patchwork of different situations

The importance of fungal infections in both human and animals has increased over the last decades. This article represents an overview of the different categories of fungal infections that can be encountered in animals originating from environmental sources without transmission to humans. In addition, the endemic infections with indirect transmission from the environment, the zoophilic fungal pathogens with near-direct transmission, the zoonotic fungi that can be directly transmitted from animals to humans, mycotoxicoses and antifungal resistance in animals will also be discussed. Opportunistic mycoses are responsible for a wide range of diseases from localized infections to fatal disseminated diseases, such as aspergillosis, mucormycosis, candidiasis, cryptococcosis and infections caused by melanized fungi. The amphibian fungal disease chytridiomycosis and the Bat White-nose syndrome are due to obligatory fungal pathogens. Zoonotic agents are naturally transmitted from vertebrate animals to humans and vice versa. The list of zoonotic fungal agents is limited but some species, like Microsporum canis and Sporothrix brasiliensis from cats, have a strong public health impact. Mycotoxins are defined as the chemicals of fungal origin being toxic for warm-blooded vertebrates. Intoxications by aflatoxins and ochratoxins represent a threat for both human and animal health. Resistance to antifungals can occur in different animal species that receive these drugs, although the true epidemiology of resistance in animals is unknown, and options to treat infections caused by resistant infections are limited.

New insights in dermatophyte research

Dermatophyte research has renewed interest because of changing human floras with changing socioeconomic conditions, and because of severe chronic infections in patients with congenital immune disorders. Main taxonomic traits at the generic level have changed considerably, and now fine-tuning at the species level with state-of-the-art technology has become urgent. Research on virulence factors focuses on secreted proteases now has support in genome data. It is speculated that most protease families are used for degrading hard keratin during nitrogen recycling in the environment, while others, such as Sub6 may have emerged as a result of ancestral gene duplication, and are likely to have specific roles during infection. Virulence may differ between mating partners of the same species and concepts of zoo- and anthropophily may require revision in some recently redefined species. Many of these questions benefit from international cooperation and exchange of materials. The aim of the ISHAM Working Group Dermatophytes aims to stimulate and coordinate international networking on these fungi.

Methodologies for in vitro and in vivo evaluation of efficacy of antifungal and antibiofilm agents and surface coatings against fungal biofilms

Unlike superficial fungal infections of the skin and nails, which are the most common fungal diseases in humans, invasive fungal infections carry high morbidity and mortality, particularly those associated with biofilm formation on indwelling medical devices. Therapeutic management of these complex diseases is often complicated by the rise in resistance to the commonly used antifungal agents. Therefore, the availability of accurate susceptibility testing methods for determining antifungal resistance, as well as discovery of novel antifungal and antibiofilm agents, are key priorities in medical mycology research. To direct advancements in this field, here we present an overview of the methods currently available for determining (i) the susceptibility or resistance of fungal isolates or biofilms to antifungal or antibiofilm compounds and compound combinations; (ii) the in vivo efficacy of antifungal and antibiofilm compounds and compound combinations; and (iii) the in vitro and in vivo performance of anti-infective coatings and materials to prevent fungal biofilm-based infections.