Spores are the fungal equivalent of seeds: tiny dormant packages that are tough enough to survive in the environment until they find a new place to grow. Like seeds, they germinate and grow shoots (hyphae). This picture shows a scanning electron micrograph of germinating Aspergillus fumigatus spores (provided by KM Lord and ND Read). In this picture the spores are clustered in the middle, with the germ tubes (first growing shoots) radiating outwards.
Aspergillus spores are so tiny they look like fine black dust. We all inhale hundreds every day, but in healthy people they are cleared away before they have the chance to germinate by white blood cells or by tiny hairs (cilia) that physically sweep them out of the lungs.
People who have immune deficiencies (e.g. leukaemia, AIDS, transplant recipients) or carry certain genes are unable to stop the spores from growing. Aspergillus is particularly suited to growing in the crevices formed by lung damage caused by other lung conditions (e.g. COPD) or an old infection such as tuberculosis. Eventually, the strands of fungi (hyphae) grow to form a tangled mass (mycelium) mixed in with mucus and general debris. If the resulting fungal ball is very well localised it may be possible to surgically remove that part of the lung, or the ball may be coughed up.
