Aspergillus Species in Bronchiectasis: Challenges in the Cystic Fibrosis and Non-cystic Fibrosis Airways

Bronchiectasis is a chronic irreversible airway abnormality associated with infectious agents that either cause or superinfect the airways. While the role of bacteria is well studied, much remains to be determined about fungi in both cystic fibrosis- and non-cystic fibrosis-related bronchiectasis. The airway is constantly exposed to inhaled ambient moulds of which Aspergillus represent the most ubiquitous. In a normal healthy host, this situation is of little consequence. The presence of anatomical or immunological abnormalities such as those in bronchiectasis leads to a range of fungal-related pathologies from asymptomatic airway colonization to fungal sensitization, allergic bronchopulmonary aspergillosis or chronic pulmonary aspergillosis. These entities are difficult to recognize, diagnose and treat due in part to a lack of validated biomarkers. Our true understanding of the complex relationships that regulate fungal-host interactions is still in its infancy and, several questions remain. This includes if fungal epidemiology in bronchiectasis is uniform across countries, and to what extent immunopathological mechanisms-related to fungal airway infections-occurs in different disease states. Specific triggers to allergic or infectious responses to Aspergillus require further exploration. How transition occurs between allergic and invasive phenotypes and their respective biomarkers is also important. Whether anti-fungal treatment is warranted in all cases and what the optimal management strategy is, particularly when treatment should commence and its expected duration remains unclear. Further research is clearly necessary and should be prioritized to better understand the clinical effects and impact of Aspergillus in the setting of bronchiectasis.