Aspergillosis is a fungal infection caused by Aspergillus, a species of mold that is found all over the world. More than 300 different types of Aspergillus have been identified and more are continuing to be identified. Most of these molds are harmless, however, some types can cause a variety of diseases in humans ranging from simple allergic reactions to life-threatening invasive disease. Collectively, this group of diseases is referred to as aspergillosis and is broadly broken down into three categories - allergic, chronic and invasive. Four main clinical types of aspergillosis are usually identified - allergic bronchopulmonary aspergillosis, aspergilloma, invasive aspergillosis, and chronic necrotizing aspergillosis. Aspergillosis rarely develops in healthy individuals; it is much more likely to develop in individuals with asthma, cystic fibrosis, diabetes mellitus, and lung disease or in individuals who have a weakened immune system, who take corticosteroid drugs or who have had a bone marrow or organ transplant. In most cases, aspergillosis develops when susceptible individuals breathe in (inhale) Aspergillus spores.