House Dust Mites and Allergy

1. House Dust MitesandAllergy Jeffrey D. Miller MD Assistant Clinical Professor of Pediatrics, New York Medical College

2. Disclosure: Dr. Miller is the owner and CEO of Mission: Allergy, Inc., a manufacturer and distributor of products for allergen-avoidance

3. House Dust Mites and Allergy • Anatomy and physiology of dust mites • Dust mites as allergen delivery systems • Dust mite allergen avoidance

4. House Dust Mites and Allergy Anatomy and physiology of dust mites

5. Anatomy and physiology of dust mites • Dust mites are arachnids, not insects --mites are microscopic relatives of spiders and ticks --adult mites have 8 legs, not 6 • Dust mites live near people (or other warm blooded animals), but not on them • Dust mites eat dead, shed human (and pet) skin scales. They do not bite.

6. Anatomy and physiology of dust mites • Adult dust mites are 250µ (= ¼ mm) --the threshold of visibility --easily seen under low power microscopy • Dust mites appear watery, not solid, under light microscopy • Electron microscope is only required to see fine detail

7. Anatomy and physiology of dust mites D. pteronyssinus seen through electron microscope

8. Anatomy and physiology of dust mites D. pteronyssinus seen through low-power light microscope

9. Anatomy and physiology of dust mites • Dust mites require at least 50% relative humidity to survive --dust mites absorb water osmotically through specialized organs: “supra-coxal glands” • The ideal relative humidity for mites is 75%

10. Anatomy and physiology of dust mites Supra-Coxal Glands

11. Anatomy and physiology of dust mites • Dust mites are light sensitive (although they have no eyes), and move away from the light • Dust mites are therefore not living on hard exposed surfaces, but rather borrowed into the dark recesses of soft materials: • pillows • mattresses • carpets • upholstered furniture • stuffed toys

12. Anatomy and physiology of dust mites • Dust mites live for about 80 days • A female dust mite lays about 60 eggs in her lifetime • The lifecycle includes: • Egg • Larva (6 legs) • 1st stage nymph (“protonymph”) • 2nd stage nymph (“tritonymph”) • adult

13. Anatomy and physiology of dust mites • Just as a lobster must molt its external skeleton in order to grow, dust mite larval and nymph stages must shed their external skeleton (“exoskeleton”) before growing into the next stage • These shed exoskeletons are a secondary source of mite allergen

14. Anatomy and physiology of dust mites D. pteronyssinus seen through low-power light microscope Note eggs (oval), nymphs (small), and shed exoskeletons (hollow)

15. Anatomy and physiology of dust mites Electron-microscope view of dust mite egg (with adhering fecal particles)

16. Anatomy and physiology of dust mites • Mites excrete solid waste particles • Mite waste particles are 25µ in size, the same size as pollen grains, and are easily inhaled • Digestion of nutrients continues outside of the mite’s body, due to a surrounding membrane containing digestive enzymes • Mites are coprophagic (eat their own feces), to gain additional digested nutrients

17. Anatomy and physiology of dust mites Mite poop

18. Anatomy and physiology of dust mites Close-up of mite poop

19. House Dust Mites and Allergy Dust mites as allergen delivery systems

20. Dust mites as allergen delivery systems • Mite fecal waste particles are the primary source of mite allergens • Shed exoskeletons and debris from dead mites are secondary allergen sources

21. Dust mites as allergen delivery systems • The fecal particle’s weight and size are ideal for allergen delivery • Mite feces are 25µ, and are respirable • One mite can excrete 1000 of these particles during its 80 day life

22. Dust mites as allergen delivery systems • The fecal particle’s weight and size are such that they become airborne during disturbance, but settle within 20-30 minutes • Mites waste particles become airborne when the material in which they are present is disturbed: --making a bed --putting one’s face on a pillow --walking on carpet --hugging a stuffed toy …etc.

23. Dust mites as allergen delivery systems • Many allergens occur in association with enzymes (pollens, molds, animal danders) • The digestive enzymes in the membrane surrounding the mite fecal particle aid in their reaching allergen-presenting cells, by digesting the “tight junction” between epithelial cells

24. Dust mites as allergen delivery systems • Mite feces are associated with substances, including bacterial DNA and endotoxin, that the body recognizes as belonging to primitive organisms, and which also elicit immune reactions

25. Dust mites as allergen delivery systems • Shed mite exoskeletons, and the body fragments of dead dust mites, are an additional source of mite allergens • Mite exoskeletons also contain chitin (also present in insects, shellfish, fungi, and intestinal worms), which also stimulates the immune system, producing chitinase enzymes

26. Dust mites as allergen delivery systems • Mite allergens can provoke symptoms by: --contact (conjunctivitis, eczema) --inhalation (rhinitis, asthma, eczema) --ingestion (hives, anaphylaxis)

27. Dust mites as allergen delivery systems Case report: 52 year-old dust-mite-allergic woman experienced her first episode of eye swelling and lip tingling shortly after eating pancakes made from a buttermilk pancake mix  that had been stored in a Rubbermaid container in her kitchen cabinet for several months. Three months later, while cooking pancakes from the same mix, she experienced wheezing, diffuse redness, and facial swelling that again required emergency room care.

28. Dust mites as allergen delivery systems Pancake mix seen through low-power light microscope

29. Dust mites as allergen delivery systems Case report (continued): On allergy evaluation she had positive prick skin tests to D. farinae and D. pteronyssinus (15mm wheal) and to the pancake mix (9 mm wheal). Prick skin tests to wheat were negative.

30. House Dust Mites and Allergy Dust mite allergen avoidance

31. Dust mite allergen avoidance Does allergen avoidance work?

32. Dust mite allergen avoidance “If you don’t know where you are going, you might not get there!” --Yogi Berra

33. Dust mite allergen avoidance “If you don’t ask the right question, you might not get the right answer” --me

34. Dust mite allergen avoidance “Allergen avoidance” clearly works: -removing a pet from the home -quitting an occupational exposure -moving mite-allergic patients to high altitude

35. Dust mite allergen avoidance The right question: “To what is the patient allergic; and what measures will decrease their exposure to their relevant allergens sufficiently to decrease their symptoms?”

36. Dust mite allergen avoidance The right question: “To what is the patient allergic; and what measures will decrease their exposure to their relevant allergens sufficiently to decrease their symptoms?”

37. Dust mite allergen avoidance The right question: “To what is the patient allergic; and what measures will decrease their exposure to their relevant allergens sufficiently to decrease their symptoms?”

38. Dust mite allergen avoidance

39. Dust mite allergen avoidance Methods: 1122 adults with asthma, half given impermeable encasings, half given control (permeable) encasings Results: “…there were no significant differences between …the active-intervention and control groups…” Conclusion: “the use of allergen-impermeable bed covers as a single intervention for the avoidance of mite allergen seems clinically ineffective for the routine management of asthma in primary care.”

40. Dust mite allergen avoidance In the press: CNN– “Special bed covers bring no allergy, asthma relief” Reuters Health – “If you're allergic to dust mites, using a mattress cover that blocks the bugs will probably not make you feel much better, findings from two new studies suggest.” Associated Press – “Two studies found that mite-proof bed coverings, at least by themselves, fail to relieve asthma and allergies, a perplexing discovery that challenges the frequent advice of doctors.” ABC News – “Dust-mite-proof bed covering, often recommended by doctors to help asthma and allergy patients, aren't enough to stop sufferers from wheezing and sneezing, two new studies find.”

41. Dust mite allergen avoidance BUT… • 23% of patients were active smokers • An additional 22% of patients were former smokers • Patients were excluded if they did not require daily albuterol • 55% of patients owned a cat or dog

42. Dust mite allergen avoidance

43. Dust mite allergen avoidance Background: “Children with asthma who live in the inner city are exposed to multiple indoor allergens and environmental tobacco smoke in their homes” Methods: 937 children with atopic asthma (age 5-11 years); randomized, controlled trial of environmental intervention that lasted one year and included education and remediation for exposure to both allergens and environmental tobacco smoke Results: “The observed reduction in symptoms translates into 34 fewer days with reported wheeze...in the intervention group. This effect is similar to that described in placebo controlled studies of inhaled corticosteroids.”

44. Dust mite allergen avoidance In the press:

45. Dust mite allergen avoidance Cochrane Database Review 2008 Apr 16;(2):CD001187. House dust mite control measures for asthma. Study: Meta-analysis of 54 studies of clinical effect of mite reduction measures in mite-sensitive asthmatics Results: There were no statistically significant differences either in number of patients improved, asthma symptom scores, or in medication usage. Author’s conclusions: Chemical and physical methods aimed at reducing exposure to house dust mite allergens cannot be recommended. It is doubtful whether further studies, similar to the ones in our review, are worthwhile.

46. Dust mite allergen avoidance BUT… • Environmental control measures can only be expected to decrease symptoms if they succeed in decreasing allergen levels • Two thirds of the studies included in the Cochrane meta-analysis failed to lower allergen levels • Those studies that did lower allergen levels also lowered symptoms

47. Dust mite allergen avoidance From Matthew Colloff, “Dust Mites”, Springer, 2009

48. Dust mite allergen avoidance If it is a hard surface, WIPE If it is a washable fabric, hot water WASH If it cannot be wiped or washed, ENCASE If it cannot be wiped, washed, or encased, REMOVE If the indoor air is not dry, DEHUMIDIFY

49. Dust mite allergen avoidance If it is a hard surface, WIPE If it is a washable fabric, hot water WASH If it cannot be wiped or washed, ENCASE If it cannot be wiped, washed, or encased, REMOVE If the indoor air is not dry, DEHUMIDIFY

50. Dust mite allergen avoidance If it is a hard surface, WIPE If it is a washable fabric, hot water WASH If it cannot be wiped or washed, ENCASE If it cannot be wiped, washed, or encased, REMOVE If the indoor air is not dry, DEHUMIDIFY