Significant Allergens in the UK

Aeroallergens can be generally considered as either "Indoor" or "Outdoor" allergens.

Indoor allergens include house dust mites, storage mites, flea saliva, cockroach allergens and dander. These allergens are present throughout the year and are often associated with "year–round" or perennial clinical signs, although there may be some variation in severity.

Outdoor allergens include the pollens of various grasses, weeds and trees. Initially these tend to cause seasonal pruritus, determined by the presence of the offending pollen in the environment (see Airborne Pollen Calendar).

Insects such as mosquitoes, midges, horse and stable flies can be highly problematic for some horses. In most cases this is due to a hypersensitivity reaction to the insect's saliva, which is introduced following a bite.

Cockroach allergy is common in man and animals, several allergens have been identified including saliva, faecal material, skin casts and dead bodies. Some cross reactivity exists between cockroaches and mites. The structural protein tropomyosin has been identified as a major allergen in one of the common types of cockroach that inhabit dwellings. Tropomyosins are known to be important allergens in mites including the Dermatophagoides. It is possible that tropomyosin is the basis for cross reactivity amongst cockroaches and mites (also some other invertebrates including shrimp) (Eggleston, Arruda. 2001).

Staphylococcal and Malassezia micro–organisms are carried, at various sites on the body, by many normal dogs. If the epidermal barrier is breached, due to hypersensitivity or endocrine disease for example, colonisation by either or sometimes both organisms may occur. In some individuals hypersensitivity develops and becomes a major contributary factor to the level of pruritus.

Staphylococcal and Malassezia antigens are not included in the allervet® panels but are available as individual tests.

In our experience pollens and mites are the most frequently encountered allergens with 55% of patients testing positive to mites, 55% to grasses, 45% to trees, and 40% to weeds (allervet® unpublished data).

Allergens included in the allervet® panels have been selected on the basis of both environmental and antigenic significance in the UK.

Where circumstances dictate we are able to offer "bespoke" panels, within the limits of antigen availability.

HOUSE DUST MITES

The term house dust mites relates to a large number of mites associated with dust in dwellings. Dermatophagoides farinae, the American house dust mite, and Dermatophagoides pteronyssinus, the European house dust mite, are the most commonly encountered species. There is a high degree of cross reactivity between mites within this genus, therefore testing for the most common types will identify the majority (>90%) of patients allergic to the Dermatophagoides.

Mites feed on shed skin of man and animals and thrive in warm, humid conditions. High numbers are found in mattresses, bedding, carpets, soft furnishings etc. The mite allergens are present primarily in faeces as well as live or dead mite bodies. Several mite allergens are proteolytic enzymes; it is thought that this proteolytic activity directly contributes to the allergenicity of mite proteins by facilitating penetration through mucosal surfaces (Arruda et al 2001).

Acaricidals, used to decrease numbers of viable mites, may not significantly affect the allergenic load. Control measures which are useful include vacuuming mattresses, soft furnishings etc, regularly washing or replacing cushions, quilts and other types of soft pet bedding.

Controlling humidity is of major importance, mite populations stop growing and die out when the relative humidity is reduced to <60%.

Normal, as well as hypersensitive, animals may test positive to house dust mites, therefore serological results must be evaluated in conjunction with clinical signs.

STORAGE MITES

Commonly encountered storage mites in the UK include Acarus siro, Tyrophagus putrescentiae and Lepidoglyphus destructor. Mites and their faeces are considered highly allergenic and there is little doubt that increasing numbers of dogs have raised levels of IgE to storage mite antigens. The significance of this is not entirely clear as Tyrophagus mites show cross reactivity with the Dermatophagoides spp. and some major allergens are common to T.putrescens and Acarus siro. Nevertheless, there is increasing evidence to support the role of storage mites as important allergens involved in atopic disease.

Storage mites are found in cereal based foods, their presence will eventually result in significant spoilage. Populations expand rapidly in warm humid conditions in contaminated food.

Control measures include allergen avoidance; changing the diet to tinned/wet food should be considered if hypersensitivity to storage mites is suspected. If this is not practical, dried food should be purchased in small quantities and stored in dry, airtight containers that are thoroughly cleaned once emptied. Crumbs and residue in the bottom of the container should be discarded.

After feeding it may be helpful to wipe clean the animal’s face or muzzle.

FLEA ALLERGIC DERMATITIS (FAD)

This is the most common form of allergic skin disease seen in the dog and cat and results from a hypersensitivity reaction to flea saliva.

Theoretically all animals should undergo a thorough evaluation for fleas, followed by appropriate trial therapy, before embarking on specific testing for allergy. Inclusion of flea extract in the allervet® test panels will identify those individuals who are exquisitely sensitive to flea saliva and may highlight instances where compliance with control measures could be improved.

There are likely to be cases where FAD is suspected of being the sole cause of dermatological signs, for this reason an individual test for fleas is also available.

MOULDS

Fungal spores are present indoors and are widely distributed in the outdoor environment. They may be present in bedding, soft furnishings, clothing, damp walls etc., or airborne. Fungal spores are well documented as a cause of atopic dermatitis in man. Their involvement in companion animal hypersensitivities is less clear, however approximately 8% of patients tested for allergic disease have elevated levels of fungal specific IgE (allervet® unpublished data).

POLLENS

The pollens of weeds, grasses and trees are amongst the most common causes of Type 1 hypersensitivity disease in man and animals.

Pollens show seasonal and geographic variations as regards their prevalence in the environment and are subsequently responsible for episodic manifestation of clinical signs.

The Airborne Pollen Calendar illustrates the seasonal incidence of the major pollen allergens in the UK.

THE SIGNIFICANCE OF AIRBORNE PARTICLE SIZE

The size of airborne particles determines both the time taken for them to "settle out" in still air, and their destination within the respiratory tract following inhalation.

Small particles, up to two microns, are airborne for up to six hours, following inhalation they may reach the alveoli.

Particles between two and ten microns may settle in as little as fifteen minutes, following inhalation some reach the bronchi/bronchioles. Examples include fungal spores, dander, smoke and diesel particles.

Particles between ten and twenty microns settle in four to fifteen minutes in still air. They are filtered out in the nasal cavity and do not reach the bronchi. Examples include small pollen grains, mite droppings, certain cockroach allergens and some fungal spores.

Particles larger than forty microns settle rapidly, are rarely inhaled and do not contribute significantly to allergic inhalent disease.

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