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What are fungal spores?

Fungal spores are microscopic biological particles that allow fungi to be reproduced, serving a similar purpose to that of seeds in the plant world. Fungi decompose organic waste and are essential for recycling of carbon and minerals in our ecosystem. It has been estimated that fungi recycle millions of tons of organic waste annually. There are thousands of different fungi in the world which are essential for the survival of other organisms. In addition, mushrooms and other fleshy fungi are a food source for many animals, including humans.

Health effects of fungal spores

Many fungal spores contain allergens which can trigger a range of respiratory symptoms in those susceptible, including sneezing, runny nose, mucous production, cough, congestion, sinusitis, earache, headache, wheezing, asthma and a range of bronchial symptoms and diseases. It is estimated that around 3-4% of the general population and 10% of atopic people get symptoms from fungal spores while the majority of severe asthma sufferers are allergic to them. A number of fungal spore types share similar allergens which means that those who are allergic to moulds are likely to be sensitized to multiple types. Due to the fact that the different fungi vary in the release times of their spores, some people can therefore be affected for large parts of the year.


Golden brown spores of the bracket fungi, Ganoderma sp.

The main fungal spore types triggering allergy and asthma in the UK are Alternaria, Cladosporium, Aspergillus/Penicillium and Didymella. Allergic responses to each spore type differ between individuals and the allergens vary in the severity of the allergic reaction they induce. More people are allergic to Alternaria than Cladosporium, for example, even though the latter is much more common in the air. Alternaria also produces more strongly positive reactions while Cladosporium tends to produce a milder allergic reaction. However, Cladosporium, and in particular Cladosporium herbarum, is often the major contributor to air-spora and due to its high concentrations is therefore a major cause of inhalant allergy and allergic asthma in humans. Didymella exitialis is implicated in cases of severe asthma and also cross-reacts with Alternaria. Didymella exitialis grows on cereal crops, particularly wheat and barley so the risk can increase around harvesting of these crops. In addition, Basidiospores from mushrooms, toadstools and bracket fungi and some types of yeast (e.g. Sporobolomyces and Tilletiopsis) can also be problematic.

Fungal spore seasons in the UK

 

Fungal spores are released and distributed in a variety of ways and have specific climatic requirements. Some types favour warm, dry weather and are wind-dispersed and the numbers of these can be very high in the outdoor air. Examples of these ‘dry weather’ spores include Cladosporium, Alternaria and Epicoccum. Other types need certain temperature and moisture thresholds to be reached before they are released, so a warm, humid period can also produce a high spore risk. Examples of ‘wet weather’ spores include Didymella, Sporobolomyces and Tilletiopsis. 

Seasonal Spore Summary

Fungal spores are released on a seasonal basis.  Many types can be found in the air all year round, typically peaking in the summer or late autumn.

Spore levels show trends throughout the year:

Spring: Fungal spores are generally low in number but the risk can rise to moderate in the late Spring if conditions are favourable.

Summer to early Autumn: The spore risk starts to rise in mid-June with the increase in temperatures.  The risk peaks in late June/early July and continues until late September. Typically, during the day, there will be the ‘dry-weather’ spore types of Alternaria & Cladosporium and some types of Penicillium and Aspergillus. ‘Wet-weather’ spores respond to the dew during the night, such as Didymella, Sporobolomyces and Tilletiopsis. Therefore, there are a wide range of types that can affect people during each 24 hour period. In addition, rainfall will help the production of spores which are then released after heavy the rain or during light showers or drizzly rain. There is a lower spore risk in very windy, unusually cold and dry weather.

Mid-Autumn: Many spore types are starting to decline, but the risk can be moderate to high on warmer, humid days. By the end of November, the risk decreases to low unless it is very mild and damp. The lowest risk is on dry, cold frosty days.

Winter: Winter can be okay for some sufferers of fungal spore allergies.  There will be some risk for those sensitive to Penicillium and Aspergillus spore types, particularly in January and early February.

A spore calendar is available from the Midlands Asthma and Allergy Research Association  

 

Habits and seasonality of the main allergenic spore types in the UK

Alternaria

Alternaria

Habitat / Substrates: 

Many outdoor substrates including soil, seeds and plants. Some species of Alternaria are also important crop pathogens. For example, A. brassicae causes leaf spot on brassicas such as cabbages and A. solani causes early blight (decay) of potatoes. Indoor substrates include foodstuffs, carpets, textiles and window frames. Mould colonies are usually black or grey.

Season: 

The main season is July to September but there may be some allergy risk at other times of year. In winter, there may be some risk from indoor substrates.

Allergenicity: 

High.

Alternaria Research


Aspergillus

Aspergillus/Penicillium

Habitat / Substrates:

There are many species of Aspergillus and Penicillium and they have a very wide range of substrates. Examples: A.flavus grows on corn and peanuts and A. fumigatus grows in composts, mild to warm soils and on cereals.  P. chrysogenum is found widely in nature, it is found on food in indoor substrates and is also the type used to produce Penicillin.  P.expansum is a crop pathogen, causing post-harvest rot in apples.

Season:

These species are present throughout the year, with a small peak in August/September and the highest peak January/February.

Allergenicity:

High for some types, particularly A. fumigatus and P. chrysogenum. A. fumigatus is a major cause of aspergillosis (farmer’s lung).

Aspergillus Research

Penicillium Research

 


Cladosporium

Cladosporium

Habitat / Substrates: 

This species can be found on a wide range of plant substrates and in soil. Indoor substrates include paint and textiles. The mould colonies are generally black or olive-brown to brown.

Season: 

The main season is from April to November, with a peak in July and August. At all other times of year, this species is low in concentration.

Allergenicity: High.

Cladosporium Research


Didymella

Didymella

Habitat / Substrates: 

Didymella exitialis can be found outdoors and is widespread on grasses and cereals, particularly wheat and barley. D.bryoniae attacks cucurbits such as pumpkins and D.lycopersici causes tomato stem and fruit rots.

Season: 

The main season is June to September.

Allergenicity: High. D.exitialis can cause severe asthma.

Didymella Research


Epiccocum

Epiccocum

Habitat / Substrates: 

Epiccocum can be found outdoors and is widespread on soil and plant debris. Indoor substrates include paper and textiles.

Season: 

The main season is August and September but may occur in low concentrations at other times of year.

Allergenicity: High.