Aspergillosis

Aspergillosis is an infection caused by inhalation of spores of aspergillus, a fungus that grows in decaying vegetation. Aspergillus is harmless to healthy people but may proliferate in the lungs of people with tuberculosis. It can also worsen the symptoms of asthma and may produce serious, even fatal, infection in people with reduced immunity, such as those taking immunosuppressant drugs.

Aspergillosis in detail - non-technical

Aspergillosis in more detail - technical

Aspergillosis is the name given to diseases associated with species of mould fungi of the genus Aspergillus. As such, it comprises a series of clinically distinct infections: aggressive pulmonary infections with angio-invasion and the potential for widespread systemic haematogenous spread (invasive pulmonary aspergillosis); slow but progressive paranasal sinus infection mainly seen in the tropics (paranasal aspergillus granulom); and colonization of a pre-existing space or cavity (aspergilloma) which may give rise to medical problems including severe haemorrhage. They are also associated with both superficial and subcutaneous fungal infections. Aspergillus species cause a number of different allergic disorders including asthma and allergic bronchopulmonary aspergillosis. Bullet list 1 indicates the range of diseases associated with aspergillus.

Aspergillus species are ubiquitous and have established themselves in every conceivable terrain and environment. As they propagate through the production of large number of airborne spores, exposure is difficult to avoid. Production of spores is also determined by local and environmental conditions. For example, construction or destruction of buildings and turnover of soil have been associated with focal outbreaks of infection in predisposed and immunosuppressed individuals. Susceptibility to aspergillus infections is dependent, to a large extent, on defective immunity or structural abnormalities, and therefore the major diseases caused by these organisms are usually seen in immunosuppressed individuals, including, in particular, neutropenic patients or people with anatomocal abnormalities such as lung cavities. The incidence of infection can reach high levels in certain populations such as patients following bone marrow transplantation.

Aspergillus species can produce a number of potent metabolic byproducts or myxotoxins, such as the aflatoxins produced by A. flavus which, if present in contaminated food, can induce liver necrosis.

Bullet list 1 Diseases caused by aspergillus species

Superficial infections
  • Onychomycosis
  • Otitis externa
  • Keratomycosis
Subcutaneous infections
  • Mycetoma
  • Systemic infections
  • Localized invasive aspergillosis:
    • • Aspergilloma, chronic aspergillosis of the paranasal sinuses, chromic pulmonary aspergillosis, paranasal aspergillus granuloma
  • Invasive aspergillosis with potential for systemic spread:
    • • Invasive (pulmonary) aspergillosis (common sites for dissemination are brain, liver, skin)
    • • Aspergillus endocarditis
Allergic disease
  • Asthma, allergic rhinitis,
  • Extrinsic hypersensitivity pneumonitis (A. clavatus)
  • Allergic bronchopulmonary aspergillosis
  • Allergic aspergillus sinusitis
Toxicosis
  • Mycotoxin-producing aspergilli, e.g. A. flavus—aflatoxins

The commonest human pathogen amongst the aspergillus species is A. fumigatus, followed by A. flavus which causes infections more commonly in warmer climates. A. niger causes aspergilloma rather than invasive disease but A. nidulans rarely causes mycetoma. A. terreus is sometimes found as a cause of onychomycosis. Hence aspergillus infections may present to a wide range of different specialities and, in the severely immunocompromised patient, dissemination of aspergillus through the blood stream may result in infection of almost any organ.