House dust mites are present in all our homes, regardless of our cleaning regimes. Some sources suggest 10% of dogs have significant allergies and house dust mite affects a third of these dogs. These tiny members of the spider family are invisible to the naked eye. They feed on the dead skin cells that we shed daily.
Dust mites are an important allergen in the dog(1). Although house dust mite allergy commonly causes asthma in humans, respiratory signs are uncommon in the dog (1). Instead, allergic dogs present with skin disease. This sort of allergy is called atopy as inhaled allergens cause skin disease. Other causes of atopy include grass, flower and tree pollen and food protein allergies. The immune system reacts as if these non-toxic substances are dangerous, this results in irritation and inflammation.
Allergies are increasingly common in humans and pets
Some people believe that this is because both pets and humans are exposed to less micro-organisms in their environments because of higher standards of hygiene and better anti-infection medication. This is called the hygiene hypothesis (2).
The main symptom is itchiness
Dogs with atopy scratch, lick and nibble at their skin consistently. This constant trauma causes hair loss and inflammation and will cause thickened and pigmented skin in the long-term. Atopic dogs usually scratch their armpits, groin, belly and face.
Diagnosis is a multi-step process
Initially, parasites such as fleas, sarcoptic mites and demodectic mites are ruled out by testing or treatment. Constant scratching can result in skin infections which increase itch. These infections must be treated successfully to clarify if there is an underlying allergy. Further tests may be required to rule out yeast and fungal skin disease, autoimmune disease and in rare cases, cancer. Allergy blood tests and intradermal skin tests may be used to pinpoint an individual dog’s allergen.
Certain breeds are more susceptible to atopy which suggests a genetic component
This has now been proven (3). Proteins in the body of the mites and their faeces cause the allergic reaction. Using products to kill the mites is ineffective as dead and decomposing mites elicit the allergic reaction too.
Atopic animals are usually treated with medications to reduce itch
This may include a course of corticosteroids to reduce inflammation. Anti-histamines may be used alongside topical sprays and shampoos to treat the skin inflammation. There are effective oral and injectable treatments which can be used to control the itch.
Vaccines can be made containing the substances a dog is allergic to, this is called immunotherapy. Injecting small amounts of immunotherapy vaccine can desensitise the body, reducing the allergic response.
Atopy can be managed but not cured
Reducing the number of house dust mites in the environment can reduce the severity of the disease.
House dust mites like high temperatures and high humidity (over 45%). They grow and reproduce most efficiently in damp homes but can also survive in arid environments. Central heating keeps UK homes dry throughout winter reducing house dust mite numbers. Air conditioning has the same effect.
Soft furnishings provide hiding places for house dust mites, particularly in the bedroom. Mattresses and pillows can harbour large mite populations. Covering your mattress with a fine woven fabric cover will reduce inhaled mite faeces and mite proteins. Plastic is an effective barrier but it can induce sweating when used as a mattress or pillow cover. A similar fine woven fabric cover can be used on the dog bed. Atopic dogs may be less severely affected if they don’t sleep in the bedroom.
All bedding should be washed weekly, either on a hot cycle or a warm cycle if tumble dried afterwards.
Carpets, fabric sofas, cushions and curtains also harbour mites. If possible, replace carpets with solid floors, buy leather or plastic furniture and exchange curtains for blinds. These measures reduce house dust mite populations significantly.
Keeping the house clean
Frequent vacuuming of floors and soft furnishings reduces mite numbers. There is less debris for them to feed on. As vacuuming disturbs dust and can transiently produce more dust, it is best to remove the dog for twenty minutes after vacuuming. Using double-layered vacuum bags can reduce the dust in the environment. Some vacuum cleaners have high-efficiency particulate (HEPA) filters which significantly reduce the allergens released into the environment. Steam cleaning has a beneficial effect in reducing mite numbers, but frequent vacuuming has the greatest effect (4).
Dusting and moving furniture also increase environmental contamination. If it is safe, the dog would be best in the garden or another room while the house is cleaned.
Electrostatic air purifiers with HEPA filters can be useful as they remove particles as small as tobacco smoke. However, they produce ozone, and the air flow can disturb dust so they must be carefully positioned.
Dogs with allergies to house dust mites may also be allergic to storage mites. This is a mite found in dry dog food bags after they have been open for a few days. The longer a bag is open the more storage mites will be present. Freezing and thawing the daily ration will reduce their number and signs of allergy.
Environmental control can be effective in reducing the signs of house dust mite allergy. If an allergic dog continues to scratch, then medication can be prescribed to manage the symptoms effectively.
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References
Discussion
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