Aspergillus is a genus of around 200 molds found throughout much of nature worldwide. Aspergillus was first catalogued in 1729 by the Italian priest and biologist Pier Antonio Micheli. Viewing the fungi under a microscope, Micheli was reminded of the shape of an aspergillum (holy water sprinkler), and named the genus accordingly.

Many species can cause infection in humans and other animals. Some infections found in animals have been studied for years. Some species found in animals have been described as new and specific to the investigated disease and others have been known as names already in use for organisms such as saprophytes. For humans there is a range of diseases such as infection to the external ear, skin lesions, and ulcers classed as mycetomas.

Pathogens
Some of this species of mold can cause serious disease in humans and animals, and can be pathogenic. The most common causing mold  types are Aspergillus fumigatus and Aspergillus flavus. Aspergillus flavus produces aflatoxin which is both a toxin and a carcinogen, and which can potentially contaminate foods such as nuts. The most common causing allergic disease are Aspergillus fumigatus and Aspergillus clavatus.

Aspergillosis
Aspergillosis is the group of diseases caused by Aspergillus. The most common subtype among paranasal sinus infections associated with aspergillosis is aspergillus fumigatus. The symptoms include fever, cough, chest pain or breathlessness, which also occur in many other illnesses so diagnosis can be difficult. Usually, only patients with already weakened immune systems or who suffer other lung conditions are susceptible.
In humans, the major forms of disease are:
Allergic bronchopulmonary aspergillosis or ABPA (affects patients with symptoms that produce significant respiratory morbidity such as asthma, cystic fibrosis and sinusitis).
Acute invasive aspergillosis (risk increases if patient has weakened immunity such as some AIDS patients and those undergoing chemotherapy).
Disseminated invasive aspergillosis (widespread through body).
Aspergillosis of the air passages is also frequently reported in birds, and certain species of Aspergillus have been known to infect insects.