Many readers of this blog will be familiar with Aspergillus fumigatus as the fungal species that can cause severe invasive infections amongst immunocompromised people, but in people with apparently perfectly healthy immune systems these fungi are removed by several active 'cleaning systems' present in our lungs.
There are some rare exceptions where apparently healthy people do get chronic infections caused by Aspergillus fumigatus (referred to as chronic pulmonary aspergillosis (CPA)) and these are partly explained away by them having severe scarring of their airways or lung tissue caused by infections such as Tuberculosis. Once scarred the airways tend to lose their 'cleaning system' for that area, allowing other infections to settle in.
Apart from these exceptions people with healthy immune systems are pretty safe from infection by Aspergillus - except for asthma and Allergic Bronchopulmonary Aspergillosis (ABPA).
ABPA is a well described condition effecting some immunocompetant people who develop a chronic non-invasive infection of their lungs. Patient groups vulnerable to this include asthma and cystic fibrosis. It is suggested that there are 150 000 asthmatics afflicted with ABPA in the UK alone.
Around 15-20% of asthmatics have severe asthma. Of these around 25-50%% have fungal sensitivity (SAFS), equating to around 1-3 million people in the UK+USA.
But what does fungal sensitivity mean? We all breathe in differing amounts of fungi most of the time as they are present in the air around us at all times. Are asthmatics more sensitive to these fungi or do they actually have fungi growing in their lungs - rather like we could imagine a mild form of ABPA perhaps?
Do people with fungal sensitivity have an Aspergillus infection? This question is not easy to answer but there is a quick & easy test for the presence of fungi in our airways - the sputum test. This test is a simple matter of getting the patient to expectorate sputum and then attempting to grow fungus from the sputum - a process that takes about 10-14 days. if fungi grow out of sputum then we have a fair indicator that there are fungi in the lungs of the patient, though this is not definitive.
Fairs et.el. have recently showed that there is a strong association (63% SAFS patients were positive, only 7% non-asthmatic control group were positive) between severe asthma and fungi in the sputum, so we now know that there is a very good chance that severe asthma is strongly linked with viable fungi present in the lungs of severe asthmatics.
Can we conclude that a growing fungus e.g. Aspergillus is one cause of severe asthma? It is a seductive theory with a fair body of evidence accumulating, albeit largely circumstantial. Some doctors are already treating SAFS with an antifungal medication with good success (See clinical trial here) - as you would expect if fungi are causing the severity and if evidence continues to accumulate then many more will start to do so too.
- Cystic fibrosis, atopy, asthma and ABPA
- Severe asthma and fungi: current evidence
- Denning Fungi and resp allergy BMS
- The link between fungi and severe asthma: a summary of the evidence
- Randomized Controlled Trial of Oral Antifungal Treatment for Severe Asthma with Fungal Sensitization