Allergic Bronchopulmonary Aspergillosis (ABPA) Profile I

Aspergillus species are ubiquitous environmental molds that grow on organic matter and aerosolizeconidia.^9-11 Humans inhale hundreds of conidia per day without adverse consequences, except for a small minority of people for whom infection with Aspergillus causes significant morbidity. The clinical manifestations of aspergillosis are determined by the host immune response to exposure with the spectrum ranging from a simple allergic response to local lung disease with mycelial balls to catastrophic systemic Aspergillus infection.^9,11

Aspergillus is a genus of molds that includes several hundred species that grow in nutrient-depleted environments.^9,11 These obligate aerobes are ubiquitous and can be found in virtually every oxygen-rich setting. Aspergillus molds are saprophytes that thrive on decaying organic matter. They are often found as contaminants of starchy foods and other carbon-rich substrates. They are commonly found in soil and marine habitats as well as indoor environments and in drinking water.¹⁰ Of the hundred species identified, only a few have been associated with pathology in humans.^10-12 Aspergillus fumigatus is the species most commonly associated with disease.^13,14

Aspergillus molds continuously disseminate spores (conidia) into the environment.¹⁰ Humans are constantly exposed to airborne Aspergillus spores, which, once inhaled, can access the most distal airways of the lungs due to their size and durability.⁸ In immuno-competent individuals with healthy lungs, inhaled conidia are eliminated by the neutrophils and macrophages of the innate immune system and do not lead to disease.^10,15 Illness only develops in a small proportion of patients with altered immune systems or underlying lung pathology.^9,11,16,17 Non-invasive forms of Aspergillus-induced lung disease include Allergic Bronchopulmonary Aspergillosis (ABPA)^18-20 and Chronic Pulmonary Aspergillosis (CPA).²¹ In severely immunocompromised individuals, Aspergillus infection of the respiratory system can spread to other organs in a condition referred to as Invasive Pulmonary Aspergillosis (IPA).^10,11,15 Antibody testing is central to diagnosis of these conditions, with raised Aspergillus-specific IgG often seen in patients with ABPA and CPA.²² Antibody levels are also used to monitor treatment response in these syndromes.²⁰

Allergic Bronchopulmonary Aspergillosis (ABPA)

ABPA is a relatively uncommon allergic reaction to Aspergilli that almost exclusively affects individuals with asthma or cystic fibrosis.^23,24 ABPA typically causes bronchospasm and mucus buildup resulting in coughing, breathing difficulty and airway obstruction. Bronchiectasis can develop, resulting in worsening lung function and increased risk of infection. ABPA in patients with poorly controlled asthma has also been referred to as Severe Asthma with Fungal Sensitization (SAFS).²⁵

The diagnostic criteria for ABPA include the presence of a predisposing condition (asthma or cystic fibrosis) and positive allergen specific IgE to aspergillus species, a total IgE >1000 IU/mL and blood eosinophil count >500 cells/L (in corticosteroid naïve patients).^26-28 An elevated serum aspergillus IgG also supports the diagnosis of ABPA.^6,22,29-30