house dust mites and allergy jeffrey d. miller md assistant clinical professor of pediatrics, new...

House Dust Mitesand

Allergy

Jeffrey D. Miller MDAssistant Clinical Professor of Pediatrics,

New York Medical College

Disclosure:

Dr. Miller is the owner and CEO of Mission: Allergy, Inc.,

a manufacturer and distributor of products for allergen-avoidance

House Dust Mites and Allergy

• Anatomy and physiology of dust mites• Dust mites as allergen delivery systems• Dust mite allergen avoidance


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.


• 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


D. pteronyssinus seen through electron microscope


D. pteronyssinus seen through low-power light microscope


• 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%


Supra-Coxal Glands


• 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


• 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


• 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


D. pteronyssinus seen through low-power light microscopeNote eggs (oval), nymphs (small), and shed exoskeletons (hollow)


Electron-microscope view of dust mite egg(with adhering fecal particles)


• 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


Mite poop


Close-up of mite poop


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


• 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


• 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.


• 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


• 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


• 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


• Mite allergens can provoke symptoms by:--contact (conjunctivitis, eczema)--inhalation (rhinitis, asthma, eczema)--ingestion (hives, anaphylaxis)


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.


Pancake mix seen through low-power light microscope


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.


Dust mite allergen avoidance


Does allergen avoidance work?


“If you don’t know where you are going, you might not get there!”

--Yogi Berra


“If you don’t ask the right question, you might not get the right answer”

--me


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


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?”


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.”


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.”


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


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.”


In the press:


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.


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


From Matthew Colloff, “Dust Mites”, Springer, 2009


If it is a hard surface, WIPEIf it is a washable fabric, hot water WASHIf it cannot be wiped or washed, ENCASE

If it cannot be wiped, washed, or encased, REMOVEIf the indoor air is not dry, DEHUMIDIFY


If it is a hard surface, WIPE

• Dust mites are not living (or producing allergen) on hard, wipe-able surfaces

• Allergen on those surfaces was produced elsewhere, and has settled there

• Use a microfiber dust cloth or Swiffer® to trap dust, rather than just redistributing it

• The more wipe-able the room, the better


If it is a washable fabric, hot water WASH

• Wash all bedding, including blankets, every 1-2 weeks (unless allergen-barrier comforters)

• Water need not be 130o

• 130o is the temperature that will scald mites to death—but we don’t care if they are scalded, drowned, or washed down the drain

• Even cold water will remove 90% of mites• Water at 130o is a potential hazard to children


If it is a washable fabric, hot water WASH

• Water need not be 130o

• Warm water will remove 98% of the mites• Ten minutes in a clothes dryer will kill all mites• A trick: dry clothing for 10 minutes first; then

wash, even in cold water


If it cannot be wiped or washed, ENCASE

• Encase pillows, mattress and box spring in allergen-impermeable covers

• Alternatively, replace existing pillows with new pillows made with allergen-barrier outer fabric

• Encase all pillows on the bed• As an alternative to washing, comforters may be

encased, or replaced with allergen-barrier comforters


If it cannot be wiped or washed, ENCASEEncasing types:– Vinyl (very uncomfortable)– Urethane laminate (somewhat uncomfortable)– Microfiber (allow air, heat and vapor passage)• Woven microfiber--best, if sufficiently tight• Non-woven microfiber (feel like a thick paper

towel)--allow mite colonization and allergen accumulation!!



Woven Encasing Non-woven Encasing



Woven Microfiber—light microscope view



Woven Microfiber—electron microscope view



Non-Woven Microfiber—light microscope view



Mites on WOVEN encasing—stay on surface



Mites on NON-WOVEN encasing—burrow into fabric



Encasing types:– Microfiber (allow air, heat and vapor passage)• Non-woven microfiber (feel like a thick paper

towel)--allow mite colonization and allergen accumulation! AVOID!• Woven microfiber--best, if sufficiently tight



All woven microfibers are not equal. They vary in the number and size of their pores.

Very tightly woven microfiber fabric Less tightly woven microfiber fabric


If it cannot be wiped, washed, or encased, REMOVE

• If possible, remove the bedroom carpet, leaving hardwood, tile or linoleum flooring – washable throw rugs are OK, if washed regularly

• Remove – stuffed toys– throw pillows– upholstered furniture (use wood, plastic, leather)– pennants – curtains …etc.


If the indoor air is not dry, DEHUMIDIFY• Keep humidity below 50%, if possible– obtain a humidity gauge– use air-conditioner , dehumidifier in summer– avoid winter humidifier use, or use sparingly

• Even lesser decreases in humidity (below 75%) are helpful, as they decrease dust mite growth and allergen production somewhat– less mite growth →less mite feces


If it is a hard surface, WIPEIf it is a washable fabric, hot water WASHIf it cannot be wiped or washed, ENCASE

If it cannot be wiped, washed, or encased, REMOVEIf the indoor air is not dry, DEHUMIDIFY


Do I have to do everything?


“ A chain is as strong as its weakest link”

“ If can can, if no can no can”--Hawaiian saying

Warning: paying too much attention to dust mites can lead to everything looking like a dust mite

house dust mites and allergy jeffrey d. miller md assistant clinical professor of pediatrics, new...

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