House dust mite (HDM) droppings recycle fungi

Fungal hyphae are seen emerging from house dust mite droppings

Image credited Dr Matthew J Colloff, copyright CSIRO Publishing. Dr Colloff's book 'Dust Mites' can be seen on: http://www.publish.csiro.au/pid/6022.htm.

Fifteen separate allergens have been identified in a single dropping from HDMs. Most patients are not allergic to all, but three are considered as major or common allergens. They are formally known as: Der p1, an active digestive enzyme, Der p2, not an enzyme but able to mimic a bacterial infection, and Der p23, an enzyme that is part of the film that encases the dropping.

HDMs are blind, live in colonies, cannot control their body temperatures, have no obvious respiratory system and rely upon their sense of smell for food, sex and alarm signals. To survive, the mite must live in warm, dark, still and damp environments where it can hide away from the light. With all these restrictions, the mite's very existence is remarkable.

Some of the HDM's resilience may be due to the fact that it thrives in an environment that also encourages the growth of mite food. That food includes pollen, fungi, yeasts, bacteria and plant fibres, but its favourite food is discarded skin scales covered in bacteria, water bearing fungi, decomposing lipids, and microorganisms. It's not necessarily just the skin scale that the mite loves, but its nutritious living 'cargo'.