Pathogenesis and Pathology of Invasive Aspergillosis

Purpose of Review

Invasive aspergillosis occurs in immunosuppressed individuals and is associated with high morbidity and mortality. Understanding the host defenses and pathogen characters is important in the causation of disease.

Recent Findings

Neutropenia and/or corticosteroid administration increase the risk of invasive infections and majority are due to Aspergillus fumigatus. The size of the conidia, thermotolerance, hydrophobins and melanin on conidial surface, adaptability to host environment, and angioinvasive nature contribute to pathogenecity. The large conidial size, hot and humid environment, and constant exposure to high spore content are implicated in the pathogenesis of chronic invasive infections in a normal host due to Aspergillus flavus. Pathology depends on the immune status and varies from granuloma with fibrosis or suppuration to abscess or infarction.

Summary

The risk factors and the interplay of host pathogen in the pathogenesis of invasive aspergillosis are reviewed. Genetic predisposition and identification of such genetic factors are necessary for prevention and treatment.

     

Case Series Study of Invasive Pulmonary Aspergillosis

Diagnosis of invasive pulmonary aspergillosis (IPA) is challenging. The objective of the study was to assess the value of microbiological tests to the diagnosis of IPA in the absence of non-specific radiological data. A retrospective study of 23 patients with suspicion of IPA and positivity of some microbiological diagnostic tests was performed. These tests included conventional microbiological culture, detection of Aspergillus galactomannan (GM) antigen and in some patients (1 → 3)-β-d-glucan (BDG) and Aspergillus fumigatus DNA using the LightCycler^® SeptiFast test. In 10 patients with hematological malignancy, 6 cases were considered ‘probable’ and 4 ‘non-classifiable.’ In 8 patients with chronic lung disease, 7 cases were classified as ‘probable’ and 1 as ‘proven,’ and in 5 patients with prolonged ICU stay (>7 days), there were 2 ‘proven’ cases, 2 ‘non-classifiable’ and 1 putative case. Microbiological culture was positive in 17 cases and 18 Aspergillus spp. were isolated (one mixed culture). A. fumigatus was the most frequent (44.4%) followed by A. tubingensis. The Aspergillus galactomannan (GM) antigen assay was positive in 21 cases (91.3%). The GM antigen and the (1 → 3)-β-d-glucan (BDG) assays were both performed in 12 cases (52.2%), being positive in 9. The SeptiFast test was performed in 7 patients, being positive in 4. In patients with non-classifiable pulmonary aspergillosis and one or more positive microbiological tests, radiological criteria may not be considered a limiting factor for the diagnosis of IPA.     

Solitary Pulmonary Nodules in Organ Transplant Candidates and Recipients

The solitary pulmonary nodule (SPN) is a diagnostic and therapeutic challenge in solid organ transplant patients. Common causes of SPNs in solid organ transplant recipients are fungal and bacterial infections and post-transplant lymphoproliferative disorder, which carry high morbidity and mortality. Clinical and radiographic features such as timing after transplant and patterns of SPN might provide clues to the diagnosis but are nonspecific. SPNs mandate prompt, definitive evaluation.     

Hypothermic Endpoint for an Intranasal Invasive Pulmonary Aspergillosis Mouse Model

Immunocompromised mice were infected intranasally with Aspergillus fumigatus as part of a vaccine efficacy study. Although body temperature was measured throughout the study, a formal evaluation of its usefulness as an endpoint criterion was not performed. We retrospectively evaluated survival data and temperature records to determine whether body temperature can be used as an objective predictor of death and included in the humane endpoint criteria for this mouse model. CF1 mice were immunosuppressed with either cortisone acetate or by treatment with antiGR1 (a neutrophil-depleting antibody) and then intranasally challenged with A. fumigatus. Body temperature was measured by using an infrared noncontact thermometer a maximum of 3 times daily until death or euthanasia. A surface body temperature below 29.0 °C was correlated with a poor chance of survival, and using this cutoff point with signs of morbidity (hunched, ruffled fur, respiratory distress) reliably indicates mice for euthanasia without negatively affecting data collection. Using 2 subsequent readings of less than 31.0 °C as an endpoint would have led to premature euthanasia of only one mouse (2.2%). As a single reading, a body temperature of 28.8 °C had a sensitivity of 92.2% and specificity of 90.9%. Hypothermia proved to be a useful addition to the humane endpoint criteria for this mouse model, and veterinary and research groups should discuss their study needs in relation to animal welfare to best determine the most appropriate means of including this parameter.Abbreviations: BT, body temperature; IPA, invasive pulmonary aspergillosis; ROC, receiver operator characteristicsAspergillus species ubiquitously inhabit the environment, and people inhale as many as a few hundred conidia daily.¹ The conidia of many Aspergillus species are relatively large and typically are deposited in the paranasal sinuses and upper airways, whereas A. fumigatus conidia are small enough to reach the pulmonary alveoli.¹ Although these conidia are essentially benign for healthy persons, those who are immunosuppressed can develop severe disease known as invasive pulmonary aspergillosis (IPA).⁸ This fungal disease is one of the most severe and often fatal complications associated with patients undergoing immunosuppressive treatment, such as those with hematologic malignancies who have received a hematopoietic cell transplant.³ Given the severe nature of IPA and the high mortality rate in this high-risk population, an animal model that accurately reflects the natural progression of the disease is imperative for vaccination and treatment studies.One of our investigators has been working on developing an A. fumigatus vaccine by using a murine model of aspergillosis. IPA is induced in immunosuppressed mice after intranasal inoculation. This model closely mimics the bronchopneumonia seen in human patients and therefore has historically been one of the more popular animal models for studying the disease.² Similar to the infection seen in humans, mice develop severe respiratory distress and have a high mortality rate. The mortality tends to be fairly acute, within 24 to 72 h after inoculation, and it can be very difficult to predict which mice will survive and which will eventually succumb to infection. The humane endpoints that the investigator had being using with this model were somewhat subjective. Given our goal to refine experiments as much as possible to enhance animal welfare and reduce animal suffering and morbidity, the veterinary care staff met with the investigative group in an attempt to further refine the endpoints and to include some objective criteria.Because hypothermia has been discussed as a quick and reliable indicator of mortality in several animal models,^{7,12,14-16,19-22} we investigated its use as a potential endpoint in our model. However, when looking through the literature, we were unable to find information on using body temperature (BT) measurements as a predictor of death in an animal model similar to our intranasal inoculation of Aspergillus. The publications we found mostly focused on bacterial^{12,13,15,19,20} or viral infections,^18,19,22 with only one fungal model that involved Candida albicans.^19,21 These studies recommended vastly different hypothermic endpoints, suggesting variation depending on the infectious agent, temperature recording device, and model used. For example, a study evaluating a staphylococcal enterotoxic shock model found that mice reaching a body temperature as low as 23.4 °C had an equal chance of dying or surviving,²⁰ whereas a model of influenza virus infection led to a hypothermic endpoint recommendation of 32 °C.²² The fungal infection model involved intravenous inoculation of Candida and recommended adopting an endpoint of 33.3 °C.²¹ However, the Candida study²¹ used a different fungal species and route of inoculation than did our IPA model. Given the variety of endpoints recommended for the various infectious diseases and animal models, we decided that data directly from our model were necessary to independently evaluate the usefulness of a hypothermic endpoint for our particular model of interest. BT measurements were already incorporated into the design of these studies, so we retrospectively analyzed the data in an attempt to identify a specific hypothermic endpoint for this murine model of IPA.     

Pulmonary Toxocariasis Mimicking Invasive Aspergillosis in a Patient with Ulcerative Colitis

A 45-year-old-male who had underlying ulcerative colitis and presented with fever and dry cough. Initially, the patient was considered to have invasive aspergillosis due to a positive galactomannan assay. He was treated with amphotericin B followed by voriconazole. Nevertheless, the patient deteriorated clinically and radiographically. The lung biopsy revealed eosinophilic pneumonia, and ELISA for Toxocara antigen was positive, leading to a diagnosis of pulmonary toxocariasis. After a 10-day treatment course with albendazole and adjunctive steroids, the patient recovered completely without any sequelae. Pulmonary toxocariasis may be considered in patients with subacute or chronic pneumonia unresponsive to antibiotic agents, particularly in cases with eosinophilia.     

Bone Suppression Increases the Visibility of Invasive Pulmonary Aspergillosis in Chest Radiographs

Objective

Chest radiographs (CXR) are an important diagnostic tool for the detection of invasive pulmonary aspergillosis (IPA) in critically ill patients, but their diagnostic value is limited by a poor sensitivity. By using advanced image processing, the aim of this study was to increase the value of chest radiographs in the diagnostic work up of neutropenic patients who are suspected of IPA.

Methods

The frontal CXRs of 105 suspected cases of IPA were collected from four institutions. Radiographs could contain single or multiple sites of infection. CT was used as reference standard. Five radiologists and two residents participated in an observer study for the detection of IPA on CXRs with and without bone suppressed images (ClearRead BSI 3.2; Riverain Technologies). The evaluation was performed separately for the right and left lung, resulting in 78 diseased cases (or lungs) and 132 normal cases (or lungs). For each image, observers scored the likelihood of focal infectious lesions being present on a continuous scale (0–100). The area under the receiver operating characteristics curve (AUC) served as the performance measure. Sensitivity and specificity were calculated by considering only the lungs with a suspiciousness score of greater than 50 to be positive.

Results

The average AUC for only CXRs was 0.815. Performance significantly increased, to 0.853, when evaluation was aided with BSI (p = 0.01). Sensitivity increased from 49% to 66% with BSI, while specificity decreased from 95% to 90%.

Conclusion

The detection of IPA in CXRs can be improved when their evaluation is aided by bone suppressed images. BSI improved the sensitivity of the CXR examination, outweighing a small loss in specificity.     

Pulmonary Aspergillosis

Aspergilli are widely distributed in nature and there is abundant opportunity to acquire infection. The fungus is usually only locally invasive in healthy tissues. Its culture from sputum on one occasion may have no significance. Its growth in the bronchial tree of asthmatics may produce sensitization with aggravation of the asthma and bronchial plugging. Multiplication in dead or damaged lung tissue such as infarcts is not uncommon. The fungus may also colonize pre-existing lung cavities, especially those remaining after treatment of tuberculosis. The ball of fungus produces a characteristic radiological picture, particularly on tomograms, which is usually sufficient to make the diagnosis. Hemoptysis is common. Inaction may be preferable to excision, especially in a patient with impaired lung function. Seven cases have been described to illustrate some of the features and natural history of the condition. The mounting number of sterile cavities left in lungs has increased the number of mycetomas which have developed.     

Detection of Invasive Pulmonary Aspergillosis in Haematological Malignancy Patients by using Lateral-flow Technology

Invasive pulmonary aspergillosis (IPA) is a leading cause of morbidity and mortality in haematological malignancy patients and hematopoietic stem cell transplant recipients¹. Detection of IPA represents a formidable diagnostic challenge and, in the absence of a ''gold standard'', relies on a combination of clinical data and microbiology and histopathology where feasible. Diagnosis of IPA must conform to the European Organization for Research and Treatment of Cancer and the National Institute of Allergy and Infectious Diseases Mycology Study Group (EORTC/MSG) consensus defining "proven", "probable", and "possible" invasive fungal diseases². Currently, no nucleic acid-based tests have been externally validated for IPA detection and so polymerase chain reaction (PCR) is not included in current EORTC/MSG diagnostic criteria.Identification of Aspergillus in histological sections is problematic because of similarities in hyphal morphologies with other invasive fungal pathogens³, and proven identification requires isolation of the etiologic agent in pure culture. Culture-based approaches rely on the availability of biopsy samples, but these are not always accessible in sick patients, and do not always yield viable propagules for culture when obtained.An important feature in the pathogenesis of Aspergillus is angio-invasion, a trait that provides opportunities to track the fungus immunologically using tests that detect characteristic antigenic signatures molecules in serum and bronchoalveolar lavage (BAL) fluids. This has led to the development of the Platelia enzyme immunoassay (GM-EIA) that detects Aspergillus galactomannan and a ''pan-fungal'' assay (Fungitell test) that detects the conserved fungal cell wall component (1 →3)-β-D-glucan, but not in the mucorales that lack this component in their cell walls^1,4. Issues surrounding the accuracy of these tests^1,4-6 has led to the recent development of next-generation monoclonal antibody (MAb)-based assays that detect surrogate markers of infection^1,5.Thornton⁵ recently described the generation of an Aspergillus-specific MAb (JF5) using hybridoma technology and its use to develop an immuno-chromatographic lateral-flow device (LFD) for the point-of-care (POC) diagnosis of IPA. A major advantage of the LFD is its ability to detect activity since MAb JF5 binds to an extracellular glycoprotein antigen that is secreted during active growth of the fungus only⁵. This is an important consideration when using fluids such as lung BAL for diagnosing IPA since Aspergillus spores are a common component of inhaled air. The utility of the device in diagnosing IPA has been demonstrated using an animal model of infection, where the LFD displayed improved sensitivity and specificity compared to the Platelia GM and Fungitell (1 → 3)-β-D-glucan assays⁷.Here, we present a simple LFD procedure to detect Aspergillus antigen in human serum and BAL fluids. Its speed and accuracy provides a novel adjunct point-of-care test for diagnosis of IPA in haematological malignancy patients.     

Risk Factors and Outcomes of Invasive Fungal Infections in Allogeneic Hematopoietic Cell Transplant Recipients

Allogeneic hematopoietic cell transplant (HCT) recipients are at increased risk of invasive fungal infections (IFI), which are associated with a high mortality rate. We evaluated the impact of IFI in allogeneic HCT patients. In total, 541 consecutive allogeneic HCT recipients were included. The cumulative incidence of any IFI and mold infections at 1-year post-HCT was 10 and 7%, respectively. Median times to IFI and mold infection were 200 and 210 days, respectively. There was a trend toward fewer IFI and mold infections in the last several years. Both acute graft-versus-host disease (GVHD) (OR 1.83, p = 0.05) and corticosteroid duration (OR 1.0, p = 0.026) were significantly associated with increased risk of IFI, acute GVHD (OR 2.3, p = 0.027) emerged as the most important association with mold infections. Any IFI [HR 4.1 (2.79–6.07), p < 0.0001] and mold infections [HR 3.34 (2.1–5.1), p < 0.0001] were independently associated with non-relapse mortality (NRM). This association persisted in the setting of both acute and chronic GVHD. Corticosteroid treatment for >90 days was also significantly associated with higher NRM [HR 1.9 (1.3–2.6), p < 0.0001]. This study highlights the impact of IFI on NRM among HCT patients. The decrease in number of IFI and mold infections over the last several years may reflect the benefit of prophylaxis with mold-active antifungal agents.     

侵袭性肺曲霉病10例临床分析

目的:提高对侵袭性肺曲霉病(IPA)的认识,早期诊断、早期治疗.方法:回顾性对我院10例侵袭性肺曲霉病的临床资料并进行分析.结果:10例患者均符合侵袭性肺曲霉病的诊断,6例患者通过纤支镜活检确诊,4例通过刷检及痰培养结果临床诊断,纤支镜下主要表现为粘膜充血水肿、息肉样肿物或伪膜性气道支气管炎,经伊曲康唑口服治疗,10例患者均能达到临床治愈.结论:侵袭性肺曲霉病症状不典型,纤支镜检查对早期诊断有重要意义,对于轻中症患者,伊曲康唑口服治疗经济有效.     

Fatal Invasive Pulmonary Aspergillosis in COVID-19 Patient with Acute Myeloid Leukemia in Iran

Mycopathologia - Although patients with severe immunodeficiency and hematological malignancies has been considered at highest risk for invasive fungal infection, patients with severe pneumonia due...     

Infection Control Measures to Prevent Invasive Mould Diseases in Hematopoietic Stem Cell Transplant Recipients

Invasive mould diseases, particularly aspergillosis, are important causes of morbidity and mortality in allogeneic stem cell transplant recipients. Mould spores are ubiquitous in the environment. Guidelines established by the Centers for Disease Control (CDC) and other authoritative organizations focus on approaches to reduce exposure to mould spores. These recommendations include avoidance of areas and activities expected to result in high levels of mould spores (e.g., construction, gardening) and use of specially designed units (protected environments) where additional standards (e.g., HEPA-filtered rooms) are in place to minimize mould exposure. These recommendations are based on consensus criteria and limited clinical data largely derived from single-center retrospective studies. In addition, highly immunocompromised stem cell transplant recipients are commonly managed as outpatients, where engineering standards of the inpatient protected environment are not feasible. In the absence of an outbreak with an identified environmental source (e.g., a contaminated air vent), it is not possible to reliably distinguish community-acquired from nosocomial aspergillosis. Adherence to infection control guidelines, acknowledging their limitations, combined with evidence-based targeted antifungal prophylaxis for the highest risk transplant recipients, is likely to be the most effective approach to prevent invasive mould diseases.     

Challenges in Diagnosing Invasive Pulmonary Aspergillosis in Patients With COPD and Other Chronic Lung Disorders

Invasive pulmonary aspergillosis (IPA) is a necrotizing pneumonia caused by airborne opportunistic fungi of Aspergillus species. Patients with chronic obstructive pulmonary disease (COPD) or other chronic lung disorders (CLD) have emerged to be at risk for IPA, with a related mortality rate greater than 70%. Host factors playing a role in the occurrence of IPA in CLD patients differ from those in patients with hematologic disorders and may be largely responsible for a distinct pattern of the disease. Furthermore, these host factors affect the results of standard diagnostic procedures recommended for IPA. Therefore, the diagnosis of IPA in patients with COPD and other CLD remains challenging for physicians. This review puts into perspective the host factors contributing to the pathogenesis of IPA in CLD patients and discusses the use and interpretation of the main diagnostic tools currently available.     

Antifungal Therapy for Invasive Fungal Diseases in Allogeneic Stem Cell Transplant Recipients: An Update

Invasive fungal diseases (IFDs) remain a major cause of morbidity and mortality in allogeneic stem cell transplant (SCT) recipients. While the most common pathogens are Candida spp. and Aspergillus spp., the incidence of infections caused by non-albicans Candida species as well as molds such as Zygomycetes has increased. For many years, amphotericin B deoxycholate (AMB-D) was the only available antifungal for the treatment of IFDs. Within the past decade, there has been a surge of new antifungal agents developed and added to the therapeutic armamentarium. Lipid-based formulations of amphotericin B provide an effective and less nephrotoxic alternative to AMB-D. Voriconazole has now replaced AMB-D as first choice for primary therapy of invasive aspergillosis (IA). Another extended-spectrum triazole, posaconazole, also appears to be a promising agent in the management of zygomycosis, refractory aspergillosis, and for prophylaxis. Members of the newest antifungal class, the echinocandins, are attractive agents in select infections due to their safety profile, and are a more attractive option compared to AMB-D as initial treatment for invasive candidiasis and (based on one study) challenge fluconazole for superiority in management with this mycoses. However, challenges do exist among these newer agents in very high-risk individuals like allogeneic SCT recipients, which may include adverse drug events, drug–drug interactions, variability in oral absorption, and availability of alternative formulations. The addition of newer agents has also stimulated interest in the potential application of combination therapy in serious, life-threatening infections. However, adequate studies are not available for most IFDs; thus, the clinical use of combination therapy is not evidenced based on most cases and preciseness in its use is uncertain. Finally, therapeutic drug monitoring of select antifungals (notably posaconazole and voriconazole) may play an increasing role due to significant interpatient variability in serum concentrations after standard doses.     

Ocular Complications in Renal Transplant Recipients

Twenty-five patients were examined for ocular complaints following renal transplantation. Besides the expected complications of posterior subcapsular cataract and cytomegalovirus retinitis, other findings—such as focal depigmentation of the retinal pigment epithelium, a lack of hypertensive retinopathy, elevated intraocular tensions, microaneurysms, preretinal wrinkling, serous detachments of the retina, hemorrhages and exudates—were observed.A laboratory clue to the onset of cytomegalovirus retinitis was a rapid rise in cytomegalovirus (CMV) antibody titer and a positive CMV plaque count in tissue culture.