Asthma and Allergy

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• Allergic Rhinitis and Asthma
• Immunomodulatory Therapy
• References

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• The concept of one airway
• Inhalant allergens as triggers for asthma
• Food allergy and asthma
• Allergy tests

There is a strong association between allergy (sensitisation to allergens) and asthma, although these processes appear to develop independently.¹

• Asthma is regarded as one of the final stages of the ‘atopic march', which frequently begins in infancy as food allergy and atopic dermatitis. As many as 80% of infants with early evidence of allergic disease will go on to develop asthma or allergic rhinitis.²
• Early allergic sensitisation is a major risk factor for persistent wheezing and airway hyperreactivity.^3,4
• Allergic individuals are over three times more likely to develop asthma⁵ and airway hyperresponsiveness.⁶ Around 70-90% of individuals with established asthma show hypersensitivity to one or more allergens,^6,7 and this proportion is higher among children than adults.

The concept of one airway

There is growing awareness of close functional relationships between the upper and lower respiratory tract.^8,9

• Patients with allergic rhinitis frequently have associated bronchial hyperreactivity.¹⁰
• An estimated 60-80% of asthma patients have coexisting allergic rhinitis¹¹ or inflammation of paranasal sinuses.¹²
• Treatment of allergic rhinitis improves asthma control.¹³

Inhalant allergens as triggers for asthma

Inhalant allergens are major triggers for asthma and wheezing in allergic individuals.

• In sensitised individuals, exposure to house dust mite, pollen, domestic pets, moulds and cockroaches have been shown to trigger asthma attacks or worsen symptoms.^14-20 However, allergen exposure does not necessarily correlate with clinical symptoms, because patients may be sensitised to multiple allergens and have other triggers (e.g. viral infections).
• Rarely, asthma may be triggered by inhalation of a food allergen, e.g. when cooking seafood.

Strategies to reduce exposure to inhalant allergens

Various allergen avoidance measures have been attempted. Although some can reduce allergen exposure, many are ineffective and without clear evidence that they are useful in controlling asthma.²¹ Because many allergen avoidance measures can entail significant expense and inconvenience, it is important that patients are aware that these have not been proven to be effective in controlling disease.

• House dust mite - exposure to house dust mite increases the risk of asthma exacerbations in sensitised individuals with asthma.²² Reduction in exposure to allergen triggers such as house dust mite is possible,^23-26 but may be difficult to achieve in humid climates. Meta-analyses have found no conclusive evidence that house dust mite reduction strategies are effective as prophylactic treatment in established asthma.^21,27
• Pet allergens - Pet allergen exposure can precipitate asthma or worsen asthma control.^28,29 Cat allergens in particular are ubiquitous, very difficult to eliminate even after removal of the animal,³⁰ and are frequently found in locations without cats.³¹ Whilst some individual studies point to an improvement in asthma with allergen removal, definitive evidence is still awaited.³²
• Pollens - Sensitisation to pollen from grasses, weeds and trees is common in people with asthma. Asthma symptoms can worsen during periods of high pollen counts, such as seasonal changes and after thunderstorms.³³ Pollens can be carried in the air for miles, making it difficult to effectively avoid exposure. There is limited evidence for the effectiveness of pollen avoidance strategies or their role in controlling asthma or other allergic disease.
• Moulds - exposure to aerosol moulds occurs both indoors and outdoors. Indoor exposure has been associated with wheezing and peak expiratory flow variability.^34,35 Sensitisation to moulds (Alternaria species) has been reported to be a strong risk factor for asthma in arid climates. Although some strategies may reduce indoor mould levels, a role in improving asthma control has not been demonstrated.

Although other indoor allergens such as cockroaches may be relevant in Australia, there is no evidence that strategies to reduce exposure to these allergens are effective or improve asthma control.

For more information on allergy and asthma, see: Australasian Society of Clinical Immunology and Allergy. Asthma and Allergy. Australian Government Department of Health and Ageing 2005

Detailed information on allergen avoidance measures for patients is available from the Australasian Society of Clinical Immunology and Allergy. 

Food allergy and asthma

Food allergens are uncommon triggers for asthma in any age group: as few as 2.5% of people with asthma react to foods in blinded challenges.³⁶

Sensitisation to foods is a common early manifestation of allergic disease, and a significant proportion of children with food allergies will develop inhalant allergies and allergic airway disease (asthma and/or allergic rhinitis).^37-39

• The incidence of food allergies in children appears to be increasing.^40,41 Food allergies to egg, milk and soy usually resolve in the preschool years, although allergies to other foods e.g. peanuts, nuts and shellfish are more likely to persist.
• In a minority of sensitised individuals, exposure to foods can trigger anaphylaxis with associated wheezing, which should be distinguished from asthma. Patients with anaphylaxis require treatment with adrenaline as a priority over other treatments such as bronchodilators.
• The presence of asthma has been shown to be a risk factor for fatal and near-fatal food-induced anaphylactic reactions.^42,43

All people with food allergies should be referred to a specialist with specific expertise in allergy/ immunology for assessment for relevant allergens, and for treatment advice, including food avoidance and adrenaline prescription where appropriate. Rarely, food allergens can trigger asthma when inhaled.

Poorly controlled asthma is a risk factor for fatal reactions in individuals with a history of anaphylactic allergic reactions.^36,42

Allergy tests

Correct identification of allergen trigger factors offers opportunities for appropriate allergen avoidance or for disease modification by immunotherapy, which may minimise the need for long-term drug therapy. Allergy testing:

• is recommended for patients with persistent asthma or who require regular preventer therapy.
• may be considered in patients with asthma and allergic rhinitis to clarify whether allergens are contributing to disease. If allergy is not present there is no need to consider anti-allergy measures.
• should be considered for those who request it.

Currently available allergy tests detect the presence of allergen-specific IgE. The presence of these antibodies indicates sensitisation but does not necessarily predict the presence, pattern or severity of clinical reactivity. Allergy tests should be interpreted in the clinical context in consultation with an allergy specialist or a medical specialist trained in allergy.  In Australia, testing with ryegrass and house dust mite will detect more than 95% of the IgE reactors in the community. 

• Allergy skin prick tests (SPT) detect the presence of allergen-specific IgE bound to mast cells in the skin and reflect systemic sensitisation. These in vivo tests must be performed by experienced, trained staff using standardised techniques. The tests may be inhibited by antihistamines and some other medications (e.g. tricyclic antidepressants). The positive control allows correct interpretation of validity of the allergy tests.
• Radioallergosorbent tests (RAST) or related assays detect the presence of circulating allergen-specific IgE. These tests are not affected by antihistamines and other medications, but are less sensitive than SPT. These tests are also more expensive.
• Some so-called ‘allergy tests', including Vega tests, bioelectric tests, pulse tests and applied kinesiology, have no scientific basis and therefore have no place in the clinical assessment of asthma.