Aspergillus species are ubiquitous environmental molds that grow on organic matter and aerosolized conidia (conidia is a spore produced by various fungi at the tip of a specialized hypha).

Aspergillus is a genus of molds that includes several hundred species that grow in nutrient-depleted environments.

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 condition of suffering from a disease or medical condition). 

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.

Where can they be found?

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.

Of the hundred species identified, only a few have been associated with pathology in humans.

Aspergillus molds continuously disseminate spores (conidia) into the environment.

How are humans exposed to Aspergillus?

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.

What happens in the body?

In immunocompetent individuals with healthy lungs, inhaled conidia are eliminated by the neutrophils and macrophages of the innate immune system and do not lead to disease.

Illness only develops in a small proportion of patients with altered immune systems or underlying lung pathology.

Non-invasive forms of Aspergillus-induced lung disease include Allergic Bronchopulmonary Aspergillosis (ABPA) and Chronic Pulmonary Aspergillosis (CPA).

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).