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Infectious Disease and Microbiology – Aspergillosis
Aspergillosis describes a spectrum of illnesses caused by species of Aspergillus, ranging from simple colonization or allergic reactions to localized or disseminated invasive disease. Although virtually any organ may be involved, the lungs are most commonly affected, followed by the paranasal sinuses and, less frequently, the central nervous system.
The number of Aspergillus species implicated in human disease continues to expand. Aspergillus fumigatus remains the most common cause of invasive infection, but A. flavus, A. terreus, A. niger, and A. versicolor are increasingly recognized. Invasive aspergillosis is second only to candidiasis among invasive fungal infections in immunocompromised patients. Major risk factors include granulocytopenia (the most significant), hematopoietic stem cell transplantation, solid-organ transplantation, acute leukemia, prolonged corticosteroid or cytotoxic therapy, chronic obstructive pulmonary disease treated with steroids, prolonged antibiotic use, liver failure, diabetes mellitus, chronic granulomatous disease, and advanced AIDS (CD4 count ≤50 cells/mm³). Genetic polymorphisms in Toll-like receptors 4 and 9 may influence susceptibility to invasive aspergillosis and allergic bronchopulmonary aspergillosis (ABPA), respectively.
Preventive strategies focus on environmental control, particularly during hospital construction activities, to reduce exposure to airborne conidia. High-efficiency particulate air (HEPA) filtration systems are recommended for high-risk patients. In selected individuals with prior invasive disease who may become neutropenic, antifungal prophylaxis with agents such as voriconazole or amphotericin B may be considered.
Pathophysiologically, inhaled conidia are small enough to reach the alveoli. In immunocompetent hosts, alveolar macrophages clear the spores. In immunocompromised individuals, impaired macrophage function allows germination into hyphae, triggering inflammatory cytokine release, vascular invasion, tissue necrosis, and possible hematogenous dissemination. In ABPA, colonization in atopic individuals activates TH2 CD4+ T cells, driving IgE production and eosinophilia, exacerbating asthma and potentially leading to bronchiectasis. Chronic pulmonary aspergillosis, including aspergilloma formation, often develops in patients with prior lung disease such as tuberculosis, lung cancer resection, ABPA, or bullous disease.
Clinical manifestations vary by syndrome. ABPA occurs in patients with asthma or cystic fibrosis and presents with worsening respiratory symptoms, malaise, and occasionally hemoptysis. Chronic pulmonary aspergillosis typically presents with weight loss, chronic cough, hemoptysis, dyspnea, and constitutional symptoms. Invasive aspergillosis commonly presents with fever, pleuritic chest pain, cough, dyspnea, and hemoptysis, especially in neutropenic or otherwise immunocompromised hosts.
Diagnosis depends on clinical suspicion and supportive laboratory and imaging findings. In ABPA, chest imaging may show upper-lobe infiltrates, bronchial wall thickening, bronchiectasis, or ground-glass opacities. Peripheral eosinophilia, elevated total serum IgE, positive immediate skin test to Aspergillus, and elevated serum IgG to A. fumigatus support the diagnosis. Chronic pulmonary aspergillosis is characterized radiographically by one or more lung cavities, sometimes containing a mobile aspergilloma with an air-crescent sign. Invasive aspergillosis requires demonstration of fungal invasion on tissue biopsy for definitive diagnosis. Serum galactomannan and β-glucan assays are useful adjunctive tests, particularly in high-risk patients.
Treatment depends on disease type. ABPA is managed with systemic glucocorticoids combined with itraconazole, with steroids tapered over several months when possible. Chronic pulmonary aspergillosis often requires long-term antifungal therapy, commonly with voriconazole, and in selected cases surgical resection of aspergilloma. Embolization may be used to control hemoptysis. Invasive aspergillosis is treated with voriconazole as first-line therapy. Alternatives include amphotericin B, itraconazole, or echinocandins, although combination therapy remains of uncertain benefit. Surgical debridement is recommended when feasible.
Patients with invasive disease require prompt initiation of antifungal therapy and stabilization of hemodynamic parameters. Hospital admission is warranted for unstable patients, those with significant hemoptysis, or immunocompromised individuals with fever. Long-term monitoring is essential to detect relapse, progression, or drug toxicity. Therapeutic drug monitoring of voriconazole trough levels is recommended during prolonged therapy.
Prognosis depends largely on the degree of immunosuppression and fungal burden. Complications include massive hemoptysis in chronic disease, pulmonary fibrosis and bronchiectasis in ABPA, pneumothorax, empyema, and disseminated infection in invasive disease. Central nervous system involvement may result in vascular occlusion and severe neurologic sequelae. Early recognition and aggressive management are critical to improving outcomes.
Aspergillosis describes a spectrum of illnesses caused by species of Aspergillus, ranging from simple colonization or allergic reactions to localized or disseminated invasive disease. Although virtually any organ may be involved, the lungs are most commonly affected, followed by the paranasal sinuses and, less frequently, the central nervous system.
The number of Aspergillus species implicated in human disease continues to expand. Aspergillus fumigatus remains the most common cause of invasive infection, but A. flavus, A. terreus, A. niger, and A. versicolor are increasingly recognized. Invasive aspergillosis is second only to candidiasis among invasive fungal infections in immunocompromised patients. Major risk factors include granulocytopenia (the most significant), hematopoietic stem cell transplantation, solid-organ transplantation, acute leukemia, prolonged corticosteroid or cytotoxic therapy, chronic obstructive pulmonary disease treated with steroids, prolonged antibiotic use, liver failure, diabetes mellitus, chronic granulomatous disease, and advanced AIDS (CD4 count ≤50 cells/mm³). Genetic polymorphisms in Toll-like receptors 4 and 9 may influence susceptibility to invasive aspergillosis and allergic bronchopulmonary aspergillosis (ABPA), respectively.
Preventive strategies focus on environmental control, particularly during hospital construction activities, to reduce exposure to airborne conidia. High-efficiency particulate air (HEPA) filtration systems are recommended for high-risk patients. In selected individuals with prior invasive disease who may become neutropenic, antifungal prophylaxis with agents such as voriconazole or amphotericin B may be considered.
Pathophysiologically, inhaled conidia are small enough to reach the alveoli. In immunocompetent hosts, alveolar macrophages clear the spores. In immunocompromised individuals, impaired macrophage function allows germination into hyphae, triggering inflammatory cytokine release, vascular invasion, tissue necrosis, and possible hematogenous dissemination. In ABPA, colonization in atopic individuals activates TH2 CD4+ T cells, driving IgE production and eosinophilia, exacerbating asthma and potentially leading to bronchiectasis. Chronic pulmonary aspergillosis, including aspergilloma formation, often develops in patients with prior lung disease such as tuberculosis, lung cancer resection, ABPA, or bullous disease.
Clinical manifestations vary by syndrome. ABPA occurs in patients with asthma or cystic fibrosis and presents with worsening respiratory symptoms, malaise, and occasionally hemoptysis. Chronic pulmonary aspergillosis typically presents with weight loss, chronic cough, hemoptysis, dyspnea, and constitutional symptoms. Invasive aspergillosis commonly presents with fever, pleuritic chest pain, cough, dyspnea, and hemoptysis, especially in neutropenic or otherwise immunocompromised hosts.
Diagnosis depends on clinical suspicion and supportive laboratory and imaging findings. In ABPA, chest imaging may show upper-lobe infiltrates, bronchial wall thickening, bronchiectasis, or ground-glass opacities. Peripheral eosinophilia, elevated total serum IgE, positive immediate skin test to Aspergillus, and elevated serum IgG to A. fumigatus support the diagnosis. Chronic pulmonary aspergillosis is characterized radiographically by one or more lung cavities, sometimes containing a mobile aspergilloma with an air-crescent sign. Invasive aspergillosis requires demonstration of fungal invasion on tissue biopsy for definitive diagnosis. Serum galactomannan and β-glucan assays are useful adjunctive tests, particularly in high-risk patients.
Treatment depends on disease type. ABPA is managed with systemic glucocorticoids combined with itraconazole, with steroids tapered over several months when possible. Chronic pulmonary aspergillosis often requires long-term antifungal therapy, commonly with voriconazole, and in selected cases surgical resection of aspergilloma. Embolization may be used to control hemoptysis. Invasive aspergillosis is treated with voriconazole as first-line therapy. Alternatives include amphotericin B, itraconazole, or echinocandins, although combination therapy remains of uncertain benefit. Surgical debridement is recommended when feasible.
Patients with invasive disease require prompt initiation of antifungal therapy and stabilization of hemodynamic parameters. Hospital admission is warranted for unstable patients, those with significant hemoptysis, or immunocompromised individuals with fever. Long-term monitoring is essential to detect relapse, progression, or drug toxicity. Therapeutic drug monitoring of voriconazole trough levels is recommended during prolonged therapy.
Prognosis depends largely on the degree of immunosuppression and fungal burden. Complications include massive hemoptysis in chronic disease, pulmonary fibrosis and bronchiectasis in ABPA, pneumothorax, empyema, and disseminated infection in invasive disease. Central nervous system involvement may result in vascular occlusion and severe neurologic sequelae. Early recognition and aggressive management are critical to improving outcomes.
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