Think Fungus: Take Care When Out Walking

Many of us love to take long walks in parks and the countryside with family and perhaps a dog or two. The fresh air does wonders for our mood and the exercise is usually a welcome addition to our daily activities. There is no doubt that the world outside our homes is a healthy place to spend more time in, but there are risks particularly if you have a respiratory illness or you are immunocompromised.

Fungi such as Aspergillus fumigatus have a particular liking for piles of rotting vegetation. In fact what A. fumigatus is particularly well designed for is growing within deep piles of organic matter such as we see in the autumn when leaves are falling from the trees in many parts of the world. This fungus is one of the few microbes that can carry on growing as the temperature within the rotting pile climbs to 40C and that makes it a superbly adapted leaf digesting machine. Fungi such as Aspergillus fumigatus are the reason why we are not waist deep in dead leaves every year, they break down the leaves and return the released nutrients to the soil.

Unfortunately, the ability to grow at high temperatures to digest leaves also enables A. fumigatus to grow at the high temperatures that are present inside our lungs. For the most part, even A. fumigatus cannot grow in our lungs as our bodies are very highly adapted to prevent that happening but if there is any weakness in our defences then this fungus can exploit it and cause an infection.

A few people have a defective or suppressed immune system that leaves them vulnerable to infection, usually because they have had treatment for a transplant. Some have damaged lungs after an earlier infection such as TB or damage caused by smoking (COPD). A few have genetic weakness that allows in the infection such as Cystic Fibrosis or Chronic Granulomatous Disease (CGD).

We are increasingly finding that many more people have a severe form of asthma (approximately 50% of all severe asthmatics) named Severe Asthma with Fungal Sensitivity (SAFS) that we think is caused by colonisation of their airways by Aspergillus. Similar but possibly more severe still are those who usually have asthma but who’s airways are filled with fungal growth (Allergic Bronchopulmonary Aspergillosis (ABPA)). All of these people (500 000 in the UK alone) are vulnerable to ill effects if they breathe in moulds.

If you have one of the above diseases, or even if you are just very young or elderly it would be best to be careful to avoid disturbing piles of rotting leaves, or indeed piles of anything rotting such as is found in compost heaps, stable manure, bark chippings and anything similar.

Editor-in-Chief , National Aspergillosis Centre

Editor-in-Chief, Research Associate for the National Aspergillosis Centre and PPI Lead for Respiratory Section of the Manchester Biomedical Research Centre