NOTE: For clarity we will only refer to Invasive Aspergillosis (IA) on this page. For information on Chronic Pulmonary Aspergillosis (CPA) go to this page.
The vast majority of cases of IA are the result of the patient being immunocompromised, that is to say that their immune systems are not working as efficiently as they could. The reasons for this could be one of a few causes, in order of severity of immunocompromisation:
- Chemotherapy & radiotherapy for the treatment of some cancers
- Bone marrow transplant for the treatment of some cancers e.g. leukemia
- Use of immunosuppressive drugs after a transplant
- Genetic defect e.g. Chronic Granulomatous Disorder
- Overuse of some steroids
- Some organs are 'less well' protected by the immune system as they have a less rich blood supply e.g. eyes, joints
Those infections of patients closer to the top of this list are likely to have a more rapidly progressing infection, so for example bone marrow transplant patients are retained within specially protected wards while they are more severely immunocompromised. Further down the list patients can usually be allowed home on antifungal medication.
The next most important factor in contracting an Aspergillus infection is the route of entry of the fungus. Naturally enough for an air-borne fungus those parts of the body that are most vulnerable are the lungs and sinuses - moist and thin skinned.
Most other organ infections come as a secondary infection after the body has been invaded via the lungs.
Finally there is a small group of infections caused by a breaching of the natural barrier to infection - our skin. So surgery and other wounds can rarely become infected, but in some countries eyes (keratitis) are a relatively common target.
There are one or two exceptions to these rules - the external ear canal can be infected (otomycosis), the fungus often feeding on ear wax, and finger or toenails can be attacked (onychomycosis) as they are effectively dead tissue with no immune system and can be moist - especially in poorly ventilated footwear. Skin itself is too dry as a rule, though there have been cases of plaster casts being removed to expose an aspergillus growing on top of the skin!