Emerging Aspergillus Species Almost Exclusively Associated With Primary Immunodeficiencies

Dermatitis, cellulitis, and osteomyelitis caused by Aspergillus nidulans in a horse with pituitary pars intermedia dysfunction

Clinical and histologic examination of a 12-y-old client-owned Quarter Horse gelding with pituitary pars intermedia dysfunction revealed dermatitis, cellulitis, and osteomyelitis caused by Aspergillus nidulans, confirmed by a PCR assay. This novel presentation of a fungal disease in a horse was characterized by aggressive local invasion and failure to respond to all medical therapy attempted over a 1-y period. Treatments included systemic and topical antifungals, anti-inflammatories, and use of cellular matrices. Surgical excision was not attempted but should be strongly considered early in the disease process in similar cases if clean margins can be achieved. Postmortem findings were of locally aggressive disease with no dissemination.

Drug-Resistant Aspergillus spp.: A Literature Review of Its Resistance Mechanisms and Its Prevalence in Europe

Infections due to the Aspergillus species constitute an important challenge for human health. Invasive aspergillosis represents a life-threatening disease, mostly in patients with immune defects. Drugs used for fungal infections comprise amphotericin B, triazoles, and echinocandins. However, in the last decade, an increased emergence of azole-resistant Aspergillus strains has been reported, principally belonging to Aspergillus fumigatus species. Therefore, both the early diagnosis of aspergillosis and its epidemiological surveillance are very important to establish the correct antifungal therapy and to ensure a successful patient outcome. In this paper, a literature review is performed to analyze the prevalence of Aspergillus antifungal resistance in European countries. Amphotericin B resistance is observed in 2.6% and 10.8% of Aspergillus fumigatus isolates in Denmark and Greece, respectively. A prevalence of 84% of amphotericin B-resistant Aspergillus flavus isolates is reported in France, followed by 49.4%, 35.1%, 21.7%, and 20% in Spain, Portugal, Greece, and amphotericin B resistance of Aspergillus niger isolates is observed in Greece and Belgium with a prevalence of 75% and 12.8%, respectively. The prevalence of triazole resistance of Aspergillus fumigatus isolates, the most studied mold obtained from the included studies, is 0.3% in Austria, 1% in Greece, 1.2% in Switzerland, 2.1% in France, 3.9% in Portugal, 4.9% in Italy, 5.3% in Germany, 6.1% in Denmark, 7.4% in Spain, 8.3% in Belgium, 11% in the Netherlands, and 13.2% in the United Kingdom. The mechanism of resistance is mainly driven by the TR34/L98H mutation. In Europe, no in vivo resistance is reported for echinocandins. Future studies are needed to implement the knowledge on the spread of drug-resistant Aspergillus spp. with the aim of defining optimal treatment strategies.

Central nervous system Aspergillus quadrilineatus infection in a COVID-19 patient, a case report and literature review

BACKGROUND

Viral pneumonia such as COVID-19-associated aspergillosis could increase susceptibility to fungal super-infections in critically ill patients.

METHODS

Here we report a pediatric case of Aspergillus quadrilineatus cerebral infection in a recently diagnosed COVID-19-positive patient underlying acute lymphocytic leukemia. Morphological, molecular methods, and sequencing were used to identify this emerging species.

RESULTS

Histopathological examination showed a granulomatous necrotic area containing dichotomously branching septate hyphae indicating a presumptive Aspergillus structure. The species-level identity of isolate growing on brain biopsy culture was confirmed by PCR sequencing of the β-tubulin gene as A. quadrilineatus. Using the CLSI M38-A3 broth microdilution methodology, the in vitro antifungal susceptibility testing demonstrated 0.032 μg/mL MIC for posaconazole, caspofungin, and anidulafungin and 8 μg/mL against amphotericin B. A combination of intravenous liposomal amphotericin B and caspofungin therapy for 8 days did not improve the patient's condition. The patient gradually continued to deteriorate and expired.

CONCLUSIONS

This is the first COVID-19-associated cerebral aspergillosis due to A. quadrilineatus in a pediatric patient with acute lymphocytic leukemia. However, comprehensive screening studies are highly recommended to evaluate its frequency and antifungal susceptibility profiles. Before being recommended as first-line therapy in high-risk patients, more antifungal susceptibility data are needed.

Diagnosis and Treatment of Invasive Aspergillosis Caused by Non-fumigatus Aspergillus spp

With increasing frequency, clinical and laboratory-based mycologists are consulted on invasive fungal diseases caused by rare fungal species. This review aims to give an overview of the management of invasive aspergillosis (IA) caused by non-fumigatus Aspergillus spp.-namely A. flavus, A. terreus, A. niger and A. nidulans-including diagnostic and therapeutic differences and similarities to A. fumigatus. A. flavus is the second most common Aspergillus spp. isolated in patients with IA and the predominant species in subtropical regions. Treatment is complicated by its intrinsic resistance against amphotericin B (AmB) and high minimum inhibitory concentrations (MIC) for voriconazole. A. nidulans has been frequently isolated in patients with long-term immunosuppression, mostly in patients with primary immunodeficiencies such as chronic granulomatous disease. It has been reported to disseminate more often than other Aspergillus spp. Innate resistance against AmB has been suggested but not yet proven, while MICs seem to be elevated. A. niger is more frequently reported in less severe infections such as otomycosis. Triazoles exhibit varying MICs and are therefore not strictly recommended as first-line treatment for IA caused by A. niger, while patient outcome seems to be more favorable when compared to IA due to other Aspergillus species. A. terreus-related infections have been reported increasingly as the cause of acute and chronic aspergillosis. A recent prospective international multicenter surveillance study showed Spain, Austria, and Israel to be the countries with the highest density of A. terreus species complex isolates collected. This species complex seems to cause dissemination more often and is intrinsically resistant to AmB. Non-fumigatus aspergillosis is difficult to manage due to complex patient histories, varying infection sites and potential intrinsic resistances to antifungals. Future investigational efforts should aim at amplifying the knowledge on specific diagnostic measures and their on-site availability, as well as defining optimal treatment strategies and outcomes of non-fumigatus aspergillosis.

Of Mycelium and Men: Inherent Human Susceptibility to Fungal Diseases

In medical mycology, the main context of disease is iatrogenic-based disease. However, historically, and occasionally, even today, fungal diseases affect humans with no obvious risk factors, sometimes in a spectacular fashion. The field of “inborn errors of immunity” (IEI) has deduced at least some of these previously enigmatic cases; accordingly, the discovery of single-gene disorders with penetrant clinical effects and their immunologic dissection have provided a framework with which to understand some of the key pathways mediating human susceptibility to mycoses. By extension, they have also enabled the identification of naturally occurring auto-antibodies to cytokines that phenocopy such susceptibility. This review provides a comprehensive update of IEI and autoantibodies that inherently predispose humans to various fungal diseases.

Inborn Errors of Immunity Causing Pediatric Susceptibility to Fungal Diseases

Inborn errors of immunity are a heterogeneous group of genetically determined disorders that compromise the immune system, predisposing patients to infections, autoinflammatory/autoimmunity syndromes, atopy/allergies, lymphoproliferative disorders, and/or malignancies. An emerging manifestation is susceptibility to fungal disease, caused by yeasts or moulds, in a superficial or invasive fashion. In this review, we describe recent advances in the field of inborn errors of immunity associated with increased susceptibility to fungal disease.

Hurricane María drives increased indoor proliferation of filamentous fungi in San Juan, Puerto Rico: a two-year culture-based approach

Extensive flooding caused by Hurricane María in Puerto Rico (PR) created favorable conditions for indoor growth of filamentous fungi. These conditions represent a public health concern as contamination by environmental fungi is associated with a higher prevalence of inflammatory respiratory conditions. This work compares culturable fungal spore communities present in homes that sustained water damage after Hurricane María to those present in dry, non-flooded homes. We collected air samples from 50 houses in a neighborhood in San Juan, PR, 12 and 22 months after Hurricane María. Self-reported data was used to classify the homes as flooded, water-damage or dry non-flooded. Fungi abundances, composition and diversity were analyzed by culturing on two media. Our results showed no significant differences in indoor fungal concentrations (CFU/m³) one year after the Hurricane in both culture media studied (MEA and G25N). During the second sampling period fungal levels were 2.7 times higher in previously flooded homes (Median = 758) when compared to dry homes (Median = 283), (p-value < 0.005). Fungal profiles showed enrichment of Aspergillus species inside flooded homes compared to outdoor samples during the first sampling period (FDR-adjusted p-value = 0.05). In contrast, 22 months after the storm, indoor fungal composition consisted primarily of non-sporulated fungi, most likely basidiospores, which are characteristic of the outdoor air in PR. Together, this data highlights that homes that suffered water damage not only have higher indoor proliferation of filamentous fungi, but their indoor fungal populations change over time following the Hurricane. Ultimately, after nearly two years, indoor and outdoor fungal communities converged in this sample of naturally ventilated homes.

Case Commentary: Long-term fosmanogepix use in a transplant recipient with disseminated aspergillosis caused by azole-resistant Aspergillus calidoustus

Aspergillus calidoustus is an emerging, azole-resistant, cryptic Aspergillus species in immunosuppressed patients that often features extrapulmonary involvement and carries high mortality. The case presented by J. F. Camargo, R. Jabr, A. D. Anderson, L. Lekakis, et al. (Antimicrob Agents Chemother 66:e02206-21, 2022, https://doi.org/10.1128/aac.02206-21 ) describes a transplant recipient with disseminated A. calidoustus infection who was successfully treated with surgical source control, tapering of immunosuppression, and long-term, combination antifungal treatment that included the first-in-class fosmanogepix, which targets fungal mannoprotein trafficking and anchoring.

Respiratory Failure With Aspergillus submaranianii and Lymphoplasmacystic Vasculitis

Aspergillus subramanianii is a very rare form of Aspergillus in section Circumdati. Aspergillus subramanianii has been rarely reported or ever published. IgG4 disease is an emerging disease entity that can be a diagnostic challenge. We report a critically ill patient who had invasive A subramanianii pulmonary aspergillosis and posthumous diagnosis of IgG subclass 4 interstitial lung disease.

Systemic antifungal therapy with isavuconazonium sulfate or other agents in adults with invasive mucormycosis or invasive aspergillosis (non-fumigatus): A multicentre, non-interventional registry study

BACKGROUND

Isavuconazole, administered as isavuconazonium sulfate (ISAVUSULF), is a broad-spectrum triazole agent for the treatment of invasive fungal disease. In phase 3 studies, ISAVUSULF showed comparable efficacy to voriconazole and amphotericin B for the treatment of invasive aspergillosis (IA) and invasive mucormycosis (IM), respectively.

OBJECTIVES

The objective of this study is to determine all-cause mortality and safety outcomes among adults with IM and/or IA non-fumigatus (nf) treated with ISAVUSULF or other antifungal therapies (AFT).

PATIENTS AND METHODS

This multicentre, non-interventional registry enrolled patients aged ≥18 years with IM or IA-nf who received systemic AFT from January 2016 to November 2018. Patients received primary ISAVUSULF, non-primary ISAVUSULF, or other AFT, as monotherapy or combination therapy. The primary end point was all-cause mortality at Days 42 and 84; safety outcomes were adverse drug reactions (ADRs) to ISAVUSULF.

RESULTS

Of 204 patients enrolled, 74 received primary ISAVUSULF, 30 non-primary ISAVUSULF, and 100 other AFT. All-cause mortality through Day 42 was numerically lower in the non-primary ISAVUSULF group than in the primary ISAVUSULF and other AFT groups, for patients with IM (20.0% vs. 33.3% and 41.3%, respectively) or IA-nf (0% vs. 14.8% and 17.8%, respectively). All-cause mortality tended to be lower with combination therapy than with monotherapy, except for patients with IM receiving primary ISAVUSULF. Of 111 patients receiving ISAVUSULF, 14 (12.6%) reported ADRs, of whom three (2.7%) developed serious ADRs. There were no drug-related deaths.

CONCLUSIONS

This study supports the effectiveness and tolerability of ISAVUSULF in clinical practice. Further research is required to confirm the value of ISAVUSULF combination therapy over monotherapy.

Aspergillus fumigatus and aspergillosis: From basics to clinics

The airborne fungus Aspergillus fumigatus poses a serious health threat to humans by causing numerous invasive infections and a notable mortality in humans, especially in immunocompromised patients. Mould-active azoles are the frontline therapeutics employed to treat aspergillosis. The global emergence of azole-resistant A. fumigatus isolates in clinic and environment, however, notoriously limits the therapeutic options of mould-active antifungals and potentially can be attributed to a mortality rate reaching up to 100 %. Although specific mutations in CYP 51A are the main cause of azole resistance, there is a new wave of azole-resistant isolates with wild-type CYP 51A genotype challenging the efficacy of the current diagnostic tools. Therefore, applications of whole-genome sequencing are increasingly gaining popularity to overcome such challenges. Prominent echinocandin tolerance, as well as liver and kidney toxicity posed by amphotericin B, necessitate a continuous quest for novel antifungal drugs to combat emerging azole-resistant A. fumigatus isolates. Animal models and the tools used for genetic engineering require further refinement to facilitate a better understanding about the resistance mechanisms, virulence, and immune reactions orchestrated against A. fumigatus. This review paper comprehensively discusses the current clinical challenges caused by A. fumigatus and provides insights on how to address them.

Phylogenetic Identification, Diversity, and Richness of Aspergillus from Homes in Havana, Cuba

Aspergillus is one of the most common fungal genera found indoors; it is important because it can cause a wide range of diseases in humans. Aspergillus species identification is based on a combination of morphological, physiological, and molecular methods. However, molecular methodologies have rarely been used for the identification of environmental isolates of Aspergillus in Cuba. Therefore, the objective of this work was to identify the species of the genus Aspergillus obtained from houses in Havana, Cuba, through the construction of phylogeny from a partial sequence of the benA gene region, and to analyze the diversity and richness of Aspergillus in the studied municipalities. Isolates of Aspergillus spp. included in this study presented the typical macro- and micromorphology described for the genus. According to this polyphasic characterization, A. niger, A. flavus, A. welwitschiae, A. heteromorphus, A. sydowii, A. tamarii, A. fumigatus, A. clavatus, and A. tubingensis were the most abundant species. Most of the identified species constitute new records for outdoor and indoor environments in Cuba and contribute to the knowledge of fungal biodiversity in the country. These results constitute an alert for the health authorities of the country, since prolonged exposure of the inhabitants to Aspergillus spores can cause severe persistent asthma, among other diseases.

Genetic susceptibility to fungal infection in children

PURPOSE OF REVIEW

Fungal infections have steadily increased in incidence, emerging as a significant cause of morbidity and mortality in patients with iatrogenic immunosuppression. Simultaneously, we have witnessed a growing population of newly described inherited immune disorders that have enhanced our understanding of the human immune response against fungi. In the present review, we provide an overview and diagnostic roadmap to inherited disorders which confer susceptibility to superficial and invasive fungal infections.

RECENT FINDINGS

Inborn errors of fungal immunity encompass a heterogeneous group of disorders, some of which confer fungal infection-specific susceptibility, whereas others also feature broader infection vulnerability and/or noninfectious manifestations. Infections by Candida, Aspergillus, endemic dimorphic fungi, Pneumocystis, and dermatophytes along with their organ-specific presentations provide clinicians with important clues in the assessment of patients with suspected immune defects.

SUMMARY

The absence of iatrogenic risk factors should raise suspicion for inborn errors of immunity in children and young adults with recurrent or severe fungal diseases. Expeditious diagnosis and prompt initiation of antifungal therapy and management of complications are paramount to achieve remission of fungal disease in the setting of primary immunodeficiency disorders.

Tympanic membrane perforation secondary to Aspergillus niger otomycosis

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Aspergillus is a fungal mold, which is ubiquitous in nature.

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Aspergillosis results in significant morbidity and mortality worldwide.

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A rare case of tympanic membrane perforation secondary to Aspergillus niger otomycosis was reported.

Aspergillus niger is one of more than 340 different species belonging to the filamentous fungal genus Aspergillus. Aspergillosis can present with a wide range of clinical syndromes, and it results in significant morbidity and mortality worldwide. Here we described a rare case of the left central tympanic membrane perforation secondary to Aspergillus niger otomycosis. The patient underwent tympanoplasty with good improvement.

Primary immunodeficiencies and invasive fungal infection: when to suspect and how to diagnose and manage

PURPOSE OF REVIEW

Invasive fungal infections (IFIs) most often occur secondary to acquired immunodeficiency states such as transplantation, AIDS or immune-modulatory treatment for neoplastic and autoimmune disorders. Apart from these acquired conditions, several primary immunodeficiency disorders (PIDs) can present with IFIs in the absence of iatrogenic immunosuppression. This review highlights recent advances in our understanding of PIDs that cause IFIs, which may help clinicians in the diagnosis and management of such infections.

RECENT FINDINGS

A growing number of PIDs that cause varying combinations of invasive infections by commensal Candida, inhaled molds (primarily Aspergillus), Cryptococcus, Pneumocystis, endemic dimorphic fungi, dermatophytes, and/or agents of phaeohyphomycosis has uncovered the organ- and fungus-specific requirements for effective antifungal host defense in humans. Employing certain diagnostic algorithms tailored to the infecting fungus can facilitate the genetic diagnosis of the underlying PID, which has implications for the optimal management of affected patients.

SUMMARY

Heightened clinical suspicion is required for the diagnosis of underlying genetic defects in patients who develop IFIs in the absence of acquired immunodeficiency. Early initiation of antifungal therapy followed by long-term secondary prophylaxis is typically needed to achieve remission, but hematopoietic stem-cell transplantation may sometimes be necessary to promote immune restoration and infection control.

In vitro and in vivo characterization of two nonsporulating Aspergillus fumigatus clinical isolates from immunocompetent patients

Aspergillus fumigatus is a pathogenic fungus responsible for invasive aspergillosis (IA). Typically, it can produce abundant conidia to survive and spread. The infection by A. fumigatus usually occurs in immunocompromised patients due to failed clearance of inhaled conidia. However, the incidence of aspergillosis in immunocompetent hosts has been increasing, the pathogenesis of which is still unknown. Our team previously obtained two clinical nonsporulating A. fumigatus isolates from non-immunocompromised patients, which only have the form of hyphae. This present study demonstrated the in vitro and in vivo characteristics of the two nonsporulating A. fumigatus isolates and verified that their conidiation defects are associated to abolished expression of the sporulation-related central regulatory pathway brlA gene. In addition, we confirmed the mutation site of brlA gene (c.657_660delTCCT) contributes to the nonsporulating phenotype in one clinical isolate. Plate assay showed that the two nonsporulating isolates have a similar resistance to antifungal drugs, cell wall disturbing substances, and oxidative stress compared with the wild-type reference Af293. Most important of all, we employed an immunocompetent mouse model to mimic the pathogenesis of pulmonary aspergillosis in non-immunocompromised patients. It revealed that the hyphae of two nonsporulating isolates and Af293 have similar virulence in immunocompetent hosts. Interestingly, the hyphae fragments of Af293 but not conidia are able to induce invasive aspergillosis in immunocompetent mice. In conclusion, our study indicate that the form of hyphae may play a dominant causative role in pulmonary aspergillosis of immunocompetent hosts rather than conidia.

Aspergillus felis in Patient with Chronic Granulomatous Disease

We report a case of Aspergillus felis infection in a patient with chronic granulomatous disease who had overlapping features of invasive pulmonary aspergillosis and allergic bronchopulmonary aspergillosis. Identifying the species responsible for aspergillosis by molecular methods can be crucial for directing patient management and selection of appropriate antifungal agents.

Genetic variation and fungal infection risk: State of the art

Purpose of review

Fungal infections cause significant mortality in patients with acquired immunodeficiencies including AIDS, hematological malignancies, transplantation, and receipt of corticosteroids, biologics or small-molecule kinase inhibitors that impair key immune pathways. The contribution of several such pathways in antifungal immunity has been uncovered by inherited immunodeficiencies featuring profound fungal susceptibility. Furthermore, the risk of fungal infection in patients with acquired immunodeficiencies may be modulated by single nucleotide polymorphisms (SNPs) in immune-related genes. This review outlines key features underlying human genetic fungal predisposition.

Recent findings

The discovery of monogenic disorders that cause fungal disease and the characterization of immune-related gene SNPs that may regulate fungal susceptibility have provided important insights into how genetic variation affects development and outcome of fungal infections in humans.

Summary

Recognition of individualized genetic fungal susceptibility traits in humans should help devise precision-medicine strategies for risk assessment, prognostication and treatment of patients with opportunistic fungal infections.

Genetic diversity and antifungal susceptibility patterns of Aspergillus nidulans complex obtained from clinical and environmental sources

The molecular epidemiology and antifungal susceptibility of Aspergillus nidulans species complex has not been well studied. To evaluate the genetic diversity and antifungal susceptibility patterns of clinical and environmental isolates of A. nidulans complex. Sixty clinical and environmental isolates of Aspergillus section Nidulantes were collected from five countries (Iran, The Netherlands, Spain, Portugal and Greece). The species were molecularly identified by sequencing of β-tubulin gene. The genetic diversity of A nidulans complex isolates (n = 54) was determined with a microsatellite genotyping assay. Antifungal susceptibility profile was determined using EUCAST method. The isolates were classified as A nidulans (46.7%), A spinulosporus (26.6%), A quadrilineatus (10%), A pachycristatus (3.3%), A rugulosus (3.3%), A unguis (5%), A creber, (1.7%), A olivicola (1.7%) and A sydowii (1.7%). Thirty-four sequence types (STs) were identified among the 54 A nidulans complex isolates. A high level of genetic diversity was found among A nidulans sensu stricto strains but low diversity was found among A spinulosporus strains. Amphotericin B showed high MICs to all species. The most active azole was posaconazole (GM = 0.64 mg/L), while itraconazole showed the highest MICs among azoles (GM = 2.95 mg/L). A spinulosporus showed higher MICs than A nidulans sensu stricto for all antifungals except for micafungin and anidulafungin. Interspecies variations may result in differences in antifungal susceptibility patterns and challenge antifungal therapy in infections caused by A nidulans. Differences in the distribution of STs or persistence of multiple STs might be related to the sources of isolation and niche specialisation.

Back Pain in a 23-Year-Old Male With X-Linked Chronic Granulomatous Disease

Patients with chronic granulomatous disease are at increased risk for invasive aspergillosis. Cryptic Aspergillus species are being increasingly recognized as distinct causes of infection in this population. In this study, we describe the first case of Aspergillus udagawae vertebral osteomyelitis in a patient with X-linked chronic granulomatous disease.

Role of lipid transporters in fungal physiology and pathogenicity

The fungal cell wall and membrane are the most common targets of antifungal agents, but the potential of membrane lipid organization in regulating drug-target interactions has yet to be investigated. Energy-dependent lipid transporters have been recently associated with virulence and drug resistance in many pathogenic fungi. To illustrate this view, we discuss (i) the structural and biological aspects of ATP-driven lipid transporters, comprising P-type ATPases and ATP-binding cassette transporters, (ii) the role of these transporters in fungal physiology and virulence, and (iii) the potential of lipid transporters as targets for the development of novel antifungals. These recent observations indicate that the lipid-trafficking machinery in fungi is a promising target for studies on physiology, pathogenesis and drug development.

Efficacy of Olorofim (F901318) against Aspergillus fumigatus, A. nidulans, and A. tanneri in Murine Models of Profound Neutropenia and Chronic Granulomatous Disease

The emergence of azole resistance in Aspergillus fumigatus as well as an increasing frequency of multiresistant cryptic Aspergillus spp. necessitates exploration of new classes of antifungals. Olorofim (formerly F901318) is a new fungicidal agent that prevents the growth of ascomycetous mold species via inhibition of de novo pyrimidine biosynthesis, a mechanism of action distinct from that of currently available antifungal drugs. We studied the in vivo efficacy of olorofim intraperitoneal therapy (15 mg/kg of body weight every 8 h for 9 days) against infection with A. fumigatus, A. nidulans, and A. tanneri in both neutropenic CD-1 mice and mice with chronic granulomatous disease (CGD) (gp91 ^-/- phox mice). In the neutropenic mouse model, 80% to 88% of treated mice survived for 10 days, and in the CGD group, 63% to 88% of treated mice survived for 10 days, depending on the infecting species, while less than 10% of the mice in the control groups survived for 10 days. In the olorofim-treated groups, galactomannan levels were significantly suppressed, with lower organ fungal DNA burdens being seen for all three Aspergillus spp. Histopathological slides revealed a limited number of inflammatory foci with or without detectable fungal elements in the kidneys of neutropenic CD-1 mice and in the lungs of CGD mice. Furthermore, the efficacy of olorofim was unrelated to the triazole MICs of the infecting Aspergillus spp. These results show olorofim to be a promising therapeutic agent for invasive aspergillosis.

Menacing Mold: Recent Advances in Aspergillus Pathogenesis and Host Defense

The genus Aspergillus is ubiquitous in the environment and contains a number of species, primarily A. fumigatus, that cause mold-associated disease in humans. Humans inhale several hundred to several thousand Aspergillus conidia (i.e., vegetative spores) daily and typically clear these in an asymptomatic manner. In immunocompromised individuals, Aspergillus conidia can germinate into tissue-invasive hyphae, disseminate, and cause invasive aspergillosis. In this review, we first discuss novel concepts in host defense against Aspergillus infections and emphasize new insights in fungal recognition and signaling, innate immune activation, and fungal killing. Second, the review focuses on novel concepts of Aspergillus pathogenesis and highlights emerging knowledge regarding fungal strain heterogeneity, stress responses, and metabolic adaptations on infectious outcomes. Mechanistic insight into the host-pathogen interplay is thus critical to define novel druggable fungal targets and to exploit novel immune-based strategies to improve clinical outcomes associated with aspergillosis in vulnerable patient populations.

The molecular immunology of human susceptibility to fungal diseases: lessons from single gene defects of immunity

INTRODUCTION

Fungal diseases are a threat to human health. Therapies targeting the fungus continue to lead to disappointing results. Strategies targeting the host response represent unexplored opportunities for innovative treatments. To do so rationally requires the identification and neat delineation of critical mechanistic pathways that underpin human antifungal immunity. The study of humans with single-gene defects of the immune system, i.e. inborn errors of immunity (IEIs), provides a foundation for these paradigms. Areas covered: A systematic literature search in PubMed, Scopus, and abstracts of international congresses was performed to review the history of genetic resistance/susceptibility to fungi and identify IEIs associated with fungal diseases. Immunologic mechanisms from relevant IEIs were integrated with current definitions and understandings of mycoses to establish a framework to map out critical immunobiological pathways of human antifungal immunity. Expert opinion: Specific immune responses non-redundantly govern susceptibility to their corresponding mycoses. Defining these molecular pathways will guide the development of host-directed immunotherapies that precisely target distinct fungal diseases. These findings will pave the way for novel strategies in the treatment of these devastating infections.