Allergic Asthma: What have viruses got to do with it?

Epidemiological evidence suggests that certain viral infections not only trigger asthma-related symptoms but also contribute to allergic sensitisation and the development of asthma.

Read about the role of viruses in the development of allergic sensitisation and asthma……

Brief Statistics

1. Asthma costs 1-2% of the total health budgets in direct costs, with large indirect costs for time lost from work and reduced productivity.1
2. Survey data demonstrates that 95% of asthmatics have the dust mite allergen (Dermatophagoides pteronyssinus) within their mattress, to levels in excess of WHO guidelines.1
3. Survey data demonstrates that approximately 17% of homes are contaminated with mould. This is significant as there is strong evidence linking asthma exacerbations to contamination of the indoor environment with moulds.1
4. Since most people spend 90% of their time indoors, exposure to major allergens is significant.1
5. Up to 35% of the population demonstrate evidence of reactivity to allergens.1
6. 5-10% of the population show clinical features of one or more allergic disorders such as asthma, hay fever or eczema.1
7. The Health Survey for England (2002) reported rates of doctor-diagnosed asthma of 20.5% in 0-15 year olds and 14.5% for all ages.1
8. Repeated surveys have proven that incidence of asthma is steadily on the increase.1
9. Epidemiological evidence suggests that certain viral infections may not only trigger asthma-related symptoms but also contribute to allergic sensitisation and the development of asthma.2
10. Clinical and epidemiological observations strongly link viral infection with acute worsening of asthma in as many as 80% of cases in children and 60% in adults.3

Introduction
Allergic asthma is a chronic inflammatory lung disease characterised by airway inflammation (resulting in airway swelling), mucus hypersecretion and airway hyperreactivity in response to inhaled allergens, such as pollens, dust mite, moulds, fungal spores, etc., causing narrowing of the airways.4 Over the last few decades, there has been a dramatic increase in the prevalence of asthma and other allergic diseases in more economically developed and rapidly developing countries. As a result, they have become major public health problems and an enormous burden on health care resources. Severe asthma and systemic allergic reactions are potentially life-threatening conditions, which adversely affect the quality of life of millions of adults and children.5



Role of viruses
There is substantial evidence that respiratory viral infections are associated with the development of allergic sensitisation, asthma and other allergy-related illnesses. Several factors including age, type of virus, severity, location and timing of infection as well as the interactions with allergens and/or pollutants have been implicated in the development of allergic diseases related to viral infections, particularly asthma.2 Recent studies have shown that allergens and viruses may act together to exacerbate asthma. This indicates that domestic exposure to allergens acts in collaboration with viruses in sensitised patients (that is allergic individuals), thereby increasing the risk of hospital admission.1 Although their exact role in viral respiratory tract infections remains controversial, influenza virus (INF), respiratory syncitial virus (RSV) and Rhinovirus (RV) have been implicated in causing allergic sensitisation and the development of asthma.4 Traditionally, RSV has been considered as the most frequent cause of respiratory symptoms in preschool children, whilst in older children and adults, RV accounts for more than 50% of viral-triggered exacerbations.2, 3 What is peculiar about RSV is that unlike many other viral infections, it regularly re-infects children and adults. As with exposure to allergens, the age at first infection may play an important role in the subsequent response to re-infection at a later age; this fact is especially important in children of preschool age. Exposure to both allergens and viruses can occur anywhere: at home, in offices, factories, schools, etc.

Current preventative measures for viral allergic asthma exacerbation
Current preventative measures include,
1. Vaccination: This is often given in early childhood and some evidence suggests that some vaccines might influence the development of allergy. However, no clinical trials have been done to assess the immune modulatory effect of vaccination in the primary prevention of allergy. There is also no feasible vaccination against viruses such as rhinovirus.5
2. Antiviral Agents: There is currently no specific agent active against the human rhinovirus, which is the main cause for viral-triggered asthma exacerbations in adults and children. Several potential antiviral compounds are being evaluated, and some have reached clinical trial testing.3
3. In the absence of the effective strategies to control viruses, a reduced exposure to allergens is also a preventative measure; however, how feasible is this? 1
4. Air quality solutions such as air purifiers and air sterilisers, which are becoming increasingly popular.

Recommended products include,
1. The 5000 Exec-UV
2. The Airfree Air Sterilizer
3. The LightAir Air Ionizer


Useful link
http://www.airpurifierstop.com/alerts/57/how-do-air-purifiers-help-asthma-symptoms/


References
1. Green, R. M. et al. (2002) Synergism betweens allergens and viruses and risk of hospital admission with asthma: case-control study, British Medical Journal; 324: 1-5.
2. Xepapadaki, P. et al. (2007) Viral infections and allergies, Immunobiology; 212 (6): 453-9.
3. Tan, W. C. (2005) Viruses in Asthma Exacerbation, Current Opinion in Pulmonary Medicine; 11(1): 21-26.
4. van Rajit, L. S. et al (2005) Respiratory viral infections and asthma pathogenesis: A critical role for dendritic cells?, Journal of Clinical Virology; 34: 161-169.
5. Arshad, S. H., Primary prevention of asthma and allergy, Current Reviews of Allergy and Clinical Immunology; 116: 3-14.



Disclaimer
This article is only for informative purposes. It is not intended to be a medical advice and is not a substitute for professional medical advice. Please consult your doctor for all your medical concerns. Kindly follow any information given in this article only after consulting your doctor or qualified medical professional. The author is not liable for any outcome or damage resulting from any information obtained from this article.