Invasive aspergillosis is a serious fungal infection caused by Aspergillus, a common mold found widely in the environment. While most people inhale Aspergillus spores without ill effects, this infection primarily affects individuals with weakened immune systems. Invasive aspergillosis is not contagious and cannot spread from person to person or from animals to people through respiratory droplets.
Risk Factors and Susceptibility
Compromised immune systems make individuals susceptible to invasive aspergillosis, as their bodies struggle to fight off inhaled fungal spores. A significant risk group includes patients undergoing chemotherapy for cancer, especially those with hematological malignancies, due to the resulting prolonged decrease in white blood cells (neutropenia).
Recipients of hematopoietic stem cell transplants or solid organ transplants also face elevated risk, largely due to the intense immunosuppressive medications required to prevent organ rejection. Patients on high-dose or long-term corticosteroid therapy are another vulnerable population, as these medications suppress the immune response.
Severe underlying lung conditions, such as chronic obstructive pulmonary disease (COPD), emphysema, or recovery from severe viral infections like influenza or COVID-19, also increase risk. Damaged lung tissue provides an environment for fungal infection.
Specific inherited immune disorders, such as Chronic Granulomatous Disease (CGD), also predispose individuals to invasive aspergillosis. These genetic conditions impair the body’s ability to produce reactive oxygen species, which are normally used by immune cells to destroy fungal pathogens. Other factors like uncontrolled diabetes, kidney or liver failure, and malnutrition can further increase susceptibility.
Symptoms and Complications
Typical pulmonary symptoms include a persistent fever that does not respond to standard antibiotic treatments, a cough that may produce sputum or even blood (hemoptysis), chest pain, and shortness of breath. These symptoms can sometimes be difficult to distinguish from those of a patient’s underlying medical conditions.
A serious complication is dissemination, where Aspergillus spreads from the lungs through the bloodstream to other organs. This can lead to distinct symptoms depending on the affected body part. For instance, brain infection can cause abscesses, leading to headaches or neurological symptoms.
Infection spreading to the kidneys, heart, or skin can also occur, leading to organ dysfunction or visible skin lesions. Invasive aspergillosis progresses rapidly, and symptoms often become apparent once the disease is already advanced. Untreated, this widespread form of the infection can be fatal.
The Diagnostic Process
Diagnosing invasive aspergillosis is challenging due to symptom overlap with other severe conditions in immunocompromised patients. Doctors combine several approaches, including imaging tests, to confirm the infection and visualize lung changes.
A computed tomography (CT) scan of the chest is a common imaging tool, as it can reveal characteristic signs of invasive aspergillosis, such as nodules, cavities, or the “halo sign” (a hazy area surrounding a nodule). These findings suggest fungal growth within the lung tissue and prompt further investigation.
Laboratory tests identify fungal components. Blood tests like the galactomannan antigen test detect a polysaccharide in Aspergillus cell walls. The beta-D-glucan test identifies a cell wall component present in most fungi, though not specific to Aspergillus. These biomarker tests aid early detection in high-risk patients.
The most definitive diagnosis often comes from a tissue sample. A biopsy, typically from affected lung tissue, allows direct microscopic observation of the fungus, looking for characteristic septate, acutely branching hyphae. Growing the fungus from the sample (culture) further confirms Aspergillus. However, biopsy is invasive and may not be feasible for severely ill patients.
Treatment Approaches
Treatment for invasive aspergillosis primarily involves antifungal medications, and timely intervention significantly influences the outcome. The main class of drugs used are triazoles, which work by inhibiting ergosterol synthesis, a substance found in fungal cell membranes. Voriconazole is a widely used first-line therapy, demonstrating improved outcomes in many patients.
Isavuconazole is another triazole with comparable efficacy. Other antifungals, like polyenes such as amphotericin B (often in lipid formulations to reduce side effects), may be used if patients cannot tolerate or do not respond to triazoles. Echinocandins, targeting the fungal cell wall, are sometimes used as salvage therapy or in combination for severe cases.
Surgery plays a more limited role in the management of invasive aspergillosis. It is typically reserved for specific situations, such as removing a localized fungal mass (aspergilloma) that is causing symptoms like bleeding, or to address infections in specific sites like the sinuses or bones. Surgical intervention is generally considered alongside antifungal drug therapy rather than as a standalone treatment.
Prevention and Outlook
Preventing invasive aspergillosis in high-risk individuals involves a combination of strategies. Prophylactic antifungal medication, often with broad-spectrum azoles like posaconazole, is recommended for certain patient groups, such as those undergoing hematopoietic stem cell transplantation or with severe graft-versus-host disease. These medications aim to prevent the infection from taking hold during periods of immune vulnerability.
Environmental controls are also implemented to reduce exposure to Aspergillus spores. This includes avoiding dusty areas like construction or excavation sites, as these environments can have high concentrations of fungal spores. In hospital settings, protective environments with High-Efficiency Particulate Air (HEPA) filtration systems and positive air pressure rooms are utilized to minimize airborne spore levels for susceptible patients.
The outlook for individuals with invasive aspergillosis depends on several factors: overall underlying health, immune system impairment, and promptness of diagnosis and treatment. Despite advancements, it remains a serious condition with substantial morbidity and mortality, underscoring the importance of early detection and aggressive management.