Dust Mites Love Fungi

AATCC Dust Mite and Anti-fungal Testing

Dust Mites Love Fungi


As a microbial enthusiast, the interaction between humans and our unseen environment is fascinating.  As part of our profession we are regularly challenged with issues related to the generic categories of microorganisms such as bacteria and fungi.  But on occasion other classes of organisms such as small insects become important.  Dust mites due to their small size and association with hygiene are precisely one of these insects.  The degree to which dust mites occupy your thoughts largely depends on one’s individual allergic sensitivity to their presence.

Dust mites have been recognized from the earliest days of the microscope.   From early studies of these insects the environment that they thrive in is closely related to humans and other animals.   In human environments, it is estimated that 60 to 90% of the material we recognize as dust is derived from dead skin cells.  The dust and dander we slough off doesn’t just go away;  it becomes a preferred food source for these resourceful little critters. Over time dust mite populations grow because of the interdependent and fascinating relationship between humans, other animals and other organisms such as fungi.

Fungi are one key to the relationship between dust mites and their co-enablers: us and other animals. The presence of fungi (and other microorganisms) helps to convert part of the dust into something dust mites can more readily consume.  Why dust mites need fungi and bacteria to participate in their life cycle is not completely understood; what is kn

Mites on Cotton

own is that fungi colonize skin flakes from humans and animals and then are subsequently fed on by the dust mites.  Fungal spore are unharmed by the mites digestive system and so successive generations of fungi can still thrive after ingestion and as their primary food source is replenished, continue to provide the mite with their needed nutrition. It’s a self-perpetuating feedback loop in an almost literal sense: The fungus eats the dust, the mite eats the fungus, and the fungus survives digestion to eat more dust and become mite fodder once more.
Given their small size and relatively harmless demeanor there’s only one thing getting in the way of a happy ending: the dust mites prolific production of fecal waste.  In addition to being unpleasant there are hundreds of human allergens present in dust mite feces. The amount of allergens (allergy causing agent) present is directly related to the duration, size and activity of the dust mite colonies in the home.  Strategies for controlling mites vary, but typically focus on simultaneously improving hygiene and controlling the availability of an abundant food source.  Humidity is also a factor. In geographic regions where the relative humidity is below ~70%, dust mite populations are much less likely to be associated with the major cause of allergens. This is primarily due to the requirement for water by both the mites and by fungi.Issues with Dust Mites

FIGURE: Dust mite life cycle: Nutrients to Allergens

  1. Mites have a primitive gut containing enzymes that help in digestion of complex nutrients, such as proteins, lipids (fats) and carbohydrates (sugars).  These enzymes are relatively inefficient and fungi help the process along by providing both a source of nutrients directly from the fungi, and in digestion of the complex nutrients into simpler molecules for the mites.  The net effect is that the fungi likely improve both the abundance and availability of readily digestible material for the mites.
  2. Having these nutrients available allows the mites to proliferate, (2a) typically living for 30 to 45 days with female mites producing 30 or more eggs over that time-frame. (2b) The allergens produced by the mites are carried in their feces and are composed of the actual material used in the digestions of the nutrients (the enzymes produced from their gut).

Allergies and dust mites – Allergic reactions are part of our normal immune system and these are mediated by specialized cells in our bodies.  This system of cells in our bodies and their associated responses to environmental stimuli help protect us from the infections caused by bacteria, fungi, virus, and even cancers.  Generally speaking, immune responses perform this task by recognizing the small molecules associated as foreign material.  In the case of allergic reactions, foreign material is found and consumed by these immune cells, which removes this material (also call ‘antigens’) from our bodies.   In most cases this is done with little notice, but if the concentration of antigen is high or the exposure to the antigen continues over a long period of time, more and more immune cells become involved in the process which provides extra stimulus to the immune response.  When this happens we feel it as an ‘allergic response’ or in some cases an allergic reaction.   Normally this type of response subsides once the allergen is removed (think of fall changing to winter), but in some cases the stimulation of the antigen can cause a hyper-sensitivity to the antigen leading to cold or flu like symptoms or a skin reaction such as hives.

Allergic reactions due to dust mites are more problematic than the allergens associated with changes in the seasons.  Seasonal changes happen without our input. Changing bedding and keeping textiles clean on the other hand, doesn’t. Dust mites tend to grow and thrive in the environments we co-habitat: in particular the textiles and bedding we sleep in and wear and the carpeting and upholster used in our homes.  Most importantly, controlling the food source is a key step is controlling the mite population. Regularly changing bedding and keeping clothes clean is the first step to breaking up this intricate relationship and reducing the probability of allergic reactions.

Dust Mites in our environment – Dust mites thrive in human and animal environments. It is thought that the dander of our skins cells accounts for 60 to 90% of dust.  But skin is a complicated mixture of molecules (primarily keratin) and is difficult for the little mites to consume. Mites therefore rely on fungi to convert the skin material to simpler to digest materials and fatty acids.

Dust mite controls in textiles – Insects of all sizes are difficult to control.  In all cases, if there are infestations of a given insect the most feasible method for eliminating it is to remove the infested article.  This may or may not be feasible.  Because dust mites are a universal presence in all occupied environments and because outside of the allergen issues their presence is generally innocuous, a more reliable strategy for dealing with these organisms is by eliminating the materials that encourage their growth and abundance.

Ending the relationship between dust mites and fungi, or how to ensure this story doesn’t have a happy ending

  1. General hygiene – Regular washing of articles reduces reservoirs of dust and waste materials.
  2. Create an inhospitable environment–   Lowering the humidity in a given environment (see Rule of 3 article),  will help reduce or eliminate hospitable conditions for most fungi and bacteria.  Although simple in conception this is one of the most challenging solutions.  For the common fungi associated with dust mites the relative humidity would need to be below 65 to 70% to have an impact on fungal growth.  For some home environments this may or may not be feasible.
  3. Discourage the growth of fungi with appropriate anti-fungal applications – Textiles in general are excellent targets for application of appropriate antifungal additives.  The active ingredient in anti-dandruff shampoo is one example of how these additives can be used to control unwanted fungi. Although with this example the strategy indirectly targets the reduction in available nutrients for the dust mites. It does not necessarily eliminate the repository of dust mite waste materials once the mites themselves are removed.

Contact us for more information on anti-fungal applications, dust mites, fungi and other issues related to product testing and development, to contact our laboratory please visit us online at Situ Biosciences.com