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Allergy

What is an allergy ?

Allergy is due to a hypersensitive immune system overreacting to substances that we normally shouldn’t react to because they are harmless. This includes things like pollen, dust mites and many different food products such as nuts. A severe reaction to these allergens which may be life-threatening is referred to as anaphylaxis.

Allergy in children is on the rise in Australia, with 10-15% suffering from asthma http://www.healthinsite.gov.au/topics/Asthma_Statistics ) and 40% having at least one allergic episode in childhood (http://www.allergy.org.au/content/view/182/1/) . Asthma is often of atopic origin, meaning that it is triggered by particular allergens such as dust mites, animal fur or pollen. In an atopic child, eczema is also a common condition. Other conditions caused by allergy include hives and hayfever.

There are many theories surrounding how allergies occur; one of which is the “Hygiene hypothesis” (Wills-Karp et al, 2001). This theory suggests that babies and young children whom are always in a sterile environment and thus have no exposure to pathogens (micro-organisms that can cause disease) are more likely to develop a certain subset of immune cells (Th2 T helper cells) that are associated with allergic responses. The other subset of immune cells (Th1) are more important in helping us fight off an infection, thus when under-stimulated, a drive to increase more Th2 cells may occur, predisposing the child to having allergies.

Food allergy is also relatively common, especially to allergenic products such as nuts, milk and egg. Some research at the MCRI have shown that exposure of young children to egg before 12 months reduces the chances of them becoming allergic to egg later on in life (http://www.mcri.edu.au/pages/research/news/2010/10/early-exposure-could-prevent-egg-allergy-in-babies.asp?TID=2).

Diagnosis of allergy includes the use of skin pricks where the response is recorded. An allergic reaction may appear as a red mark on the skin. Blood testing is another useful diagnostic tool.

What can be done to prevent allergy in children?

The basis of allergy and how it occurs is still yet to be fully understood. Much research has been undertaken into allergy prevention in children and there are some specific recommendations given by the Australian Society of Clinical Immunology and Allergy as shown below (Table 1,http://www.allergy.org.au/content/view/28/255/).
Although there are effective treatments in controlling allergies, a cure has not yet been discovered. One promising area of research is in the use of probiotics to treat or even prevent allergies; however more work is needed before it can be recommended as a means to prevent allergies in children (Isolauri, 2001)

TABLE : SUMMARY OF SPECIFIC RECOMMENDATIONS

Identifying infants at risk of allergic disease A family history of allergy and asthma can be used to identify children at increased risk of allergic disease
Allergen avoidance in pregnancy Dietary restrictions in pregnancy are not recommended.
Aeroallergen avoidance in pregnancy has not been shown to reduce allergic disease, and is not recommended.
Breastfeeding Breastfeeding should be recommended because of other beneficial effects.
Maternal dietary restrictions during breastfeeding are not recommended
Infant formulae In high risk infants only, If breast feeding is not possible a hydrolysed formulae is recommended (rather than conventional cows milk based formulae). Partially hydrolysed formula is available in Australia without prescription. Extensively hydrolyzed formula is more expensive, only available on prescription, and only subsidised for treatment of combined cow’s milk and soy allergic infants.Soy formulae and other formulae (eg. Goat’s milk) are not recommended for the reduction of food allergy risk.
Infant diet Complementary foods (including normal cows milk formulae) should be delayed for at least 4-6 monthsThis preventive effect has only been demonstrated in high-risk infants
There is no evidence that an elimination diet after the age of 4-6 months provides a protective effect, though this needs additional investigationAvoidance of peanut, tree nuts, and shellfish may be recommended in high risk children during the first years of life pending further study as this is unlikely to cause harm, however it must be emphasised that there is no evidence to support this recommendation.
House dust mite exposure Before definitive recommendations can be made, further research is needed to determine the relationship between early HDM exposure and the development of sensitisation and disease.No recommendation can be made at this time regarding the implementation of HDM avoidance measures for prevention of allergic disease.
Pet exposure No recommendations can be made at this time regarding exposure to pets in early life and the development of allergic disease. If a family already has pets it is not necessary to remove them, unless the child develops evidence of pet allergy (as assessed by an allergy specialist). However, at this stage we do not recommend getting new pets to reduce allergy.
Smoking and other irritants Pregnant women should be advised not to smoke in pregnancy.
Parents should be advised not to smoke.
The role of microbial agents No recommendations can be made at this time regarding the use of probiotic supplements for the prevention of allergic disease
Secondary prevention strategies Immunotherapy may be considered as a treatment option for children with allergic rhinitis, and may prevent the subsequent development of asthma.

References

  1. Opinion: The germless theory of allergic disease: revisiting the hygiene hypothesis
  2. Marsha Wills-Karp, Joanna Santeliz& Christopher L. Karp Nature Reviews Immunology 1, 69-75 (October 2001)
  3. Probiotics in human disease, Erika Isolauri, American Journal of Clinical Nutrition, Vol. 73, No. 6, 1142S-1146S, June 2001

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