Allergy and anaphylaxis

1. Allergy and anaphylaxis Dr Sid Riddington

2. Allergy: What is allergy? Allergy is a immunologically mediated hypersensitivity reaction. It is triggered by proteins in the environment that would not affect a non�allergic patient. There are approximately 18,000,000 people in the United Kingdom who suffer some form of allergy.

3. Allergy What forms of allergy are there? Grass pollen-hayfever House dust mite-allegic rhinitis. Animal dander-dog and cat allergy. Proteins in foods-food allergy Venom allergy-reactions to wasp and bee stings. Mould spores-occupational lung diseases.

4. Allergy:

5. Allergy: Allergies do tend to change with age: Classically described as the allergic march. Hayfever and rhinitis in childhood Food allergies developing in adolescence. These becoming quiescent in adult life, but incidence of asthma increasing.

6. How do we get allergy: Initial exposure Sensitization (with no initial adverse reaction) Generation of antibodies (immunoglobulin E class) Antibodies highly specific Repeated exposure Binding of antibodies to mast cells Release of mediators from mast cells.

7. How do we get allergy: Mediators exert their effects to: Make the lining of airways swell Rhinitis Conjunctivitis Laryngeal swelling Make capillaries leak fluid to give oedema Affect smooth muscle Asthma Low blood pressure

8. How do we get allergy: Allergy is a complex web of factors: Genetic: Family history is important. Small families with few children. Maternal diet and smoking. Obesity Genes linked to allergy found on chromosomes 5 & 11

9. How do we get allergy: Allergy is a complex web of factors: Environmental: Smoking household in early years. Early exposure to risky foods in diet. Air pollution Aerosols Time of year of birth (just before the pollen season)

10. How do we get allergy: Protective factors: Some viral illnesses (eg Hepatitis A and measles) Living on a farm, especially one rearing livestock Some types of intestinal microflora (Lactobacilli) BCG vaccination Heavy exposure to dog and cat allergens. The cleanliness theory of allergy.

11. Allergy: Summary. Allergy is common and increasing. Abnormal reaction to environmental chemicals Potential allergens (things that can cause allergy are legion) Initial sensitisation phase followed by reexposure. Complex and subtle web of factors including genetic, environmental and immunological factors.

12. Venom allergy Can cause severe allergic reaction About 4 deaths per year in UK (coroner�s data) Mostly caused by wasp stings Most of population exposed to wasps. Individuals get stung on average once every 10-15 years. Smaller population exposed to bee stings � BKs & family So most reactions in the larger but less stung population.

13. Venom allergy Different venoms in wasp and bee stings: Bee sting allergens Phospolipase A2 and Mellitin Wasp sting allergens Antigen 5 Both contain enzymes called hyaluronidases Sensitivity to both is very very rare.

14. Venom allergy Normal effect of either is Localised redness (erythema) Intense local pain Local oedema and swelling. A raised nettle-rash (urticaria) locally.

15. Venom allergy Allergic reactions can be local or general Local reactions affect only the area or limb of the sting. Local reactions: More extensive swelling of the hand or limb. Can lead to blistering and secondary infection. Not normally harmful Exception: A �benign� local swelling in the airway can be life-threatening.

16. Venom allergy Generalised reactions: These occur at sites remote from the sting. THEY VARY WIDELY IN SEVERITY The features of these include: Redness and itching followed by Hives (nettle rash) and facial or generalised swelling Feeling of apprehension (Impending doom)

17. Venom allergy Generalised reactions Breathing difficulties because of Swollen larynx Asthma Low blood pressure giving symptoms of Lightheadedness Giddiness Fainting or loss of consciousness

18. Venom allergy Less common features of generalised reactions include Abdominal pain Incontinence Central chest pain Visual disturbances Picture of someone having a generalised reaction is very variable.

19. Venom allergy Course of generalised reactions: Substantial proportion (20-80%) have no general reaction to subsequent stings. Spontaneous improvement. Some have much less severe general reactions. Some have a variable pattern. Children do especially well- 95% have no general reaction to subsequent sting. Course is not one of worsening reactions.

20. Venom allergy Causes for the unpredictability of reactions Elapsed time Immune response at time of sting Dose of venom Site of sting.

21. Venom allergy Managing local reactions Antihistamines Newer, rapid acting non-sedating type Double dose on stinging. Very large swellings may need intramuscular antihistamines.

22. Venom allergy Severe reactions Adrenaline 300-500 micrograms IM Nearly always effective Delay is fatal: Allows shock to develop Increases chance of treatment failure Patient may need antihistamines and steroids later.

23. Diagnosis Positive history of being stung by Skin prick testing or Blood test for bee or wasp-specific antibodies But the blood test gives a high incidence of false positives. Antibodies present but no history of allergy.

24. Treatment Desensitisation Probably only for those with severe general reactions. Time consuming and expensive Can cause anaphylaxis. Weekly injections for 3 months then Monthly injections for 3 years.