House dust mites & cockroach biology & avoidance

D u s t mi t e a n d
Co c k r o a c h :
Bi o l o g y a n d
Av o i d a n c e
Supa r a t
S i r i v i mo n p a n , M D .

CONTENTS
• Introduction
• Dust mite
– Biology
– Avoidance measures
• Cockroach
– Biology
– Avoidance measures
• Conclusions

Introduction
• The average child or adult spends at least 23 h/day indoors,
at home, in a school, or at work , little time outdoors

• This pattern has consequences for many chronic diseases but
has special significance for allergic disease

• The only diseases that have been associated statistically with
exposure to dust mite or the other indoor allergens are
chronic rhinitis, asthma, and atopic dermatitis

• Rarely, cases of conjunctivitis, urticaria, and even anaphylaxis
are associated with dust mite sensitization

Thomas A.E. Platts-Mills.Middleton‟s Allergy 7‟th edition ,539-552

Introduction

• In addition, because of the length of time spent
indoors, cumulative allergen exposure inside may be more
important than outdoor exposure


• -
-House Dust : complex mixture of
everything found in home
-Variable quantities of many allergen
- Monoclonal antibody assays
capable of measuring individual
allergens in the complex mix present in
homes


Dust mite

• Biology And Characteristic

• Pyroglyphid mites dominate
(D.pteronyssinus, D. farinae,
Euroglyphus maynei)  Dust mite
• Tropical areas: Blomia tropicalis
• Occasionally storage mites:
Lepidoglyphus destructor, Tyrophagus
putrescentior


Dust mite
• In most humid areas of the world, house dust mites are the
major source of allergens in house dust

• Pyroglyphid mites are eight-legged and sightless (microscopic
arthropods) (0.3 mm in length)

• Live on skin scales and other debris
• Very precarious water balance

• Mites growth dependent on
􀂄 water in ambient air (not capable of searching for or drinking liquids)
􀂄 relative humidity >50%
􀂄 absolute humidity ≥6 g/kg
􀂄 temperature of 65-80 F (18.3-26.7 C)

Immunol Allergy Clin N Am 31 (2011) 493–507

Dust mite
• As humidity falls,it may take months for mites to die and
longer for allergen levels to decrease in carpets, sofas,
or mattresses

• Fecal particles :
– 10-35 μm in size (similar to pollen grains)
– particles contain digestive enzymes
– surrounded by a chitinous peritrophic membrane
– „membrane‟ is not waterproof, and allergens elute
from fecal particles rapidly

• Mite bodies and fecal pellets are the major sources of allergens
•Settle out of air quickly so airborne levels depend upon disturbance in room


Dust mite
• Dust mite allergen : bed room
• Cockroach allergen : kitchen

• A major problem with any assessment of exposure to dust mite
antigens is that patients often sleep or sit with their heads very close
to mite-infested material (e.g., sofas, blankets, pillows, carpet)


Dust mite
• mite allergens are now referred to as
– group 1 (Der p 1 and Der f 1)
– group 2 (Der p 2 and Der f 2)

• Der f 1 and Der p 1 are highly cross-reactive as are Der f 2 and Der p 2
• Der f/p 10 (tropomyosin) cross reacts with other invertebrate
tropomyosins such as shrimp

• Antibodies to B. tropicalis cross-react partially with other dust mites

• dust levels of mite allergen (Der p 1 + Der p 2)
– sensitization at 2-10 μg/g of dust
– For nonallergic children higher “threshold” of 20 μg/g


Dust mite

• Avoidance measures

Otolaryngol Clin N Am 44 (2011) 711–725

Avoidance
• standard part of the treatment of allergic disease
• difficult to achieve, particularly in home environments

• Many patients, despite being skin test positive, were not aware that
dust related to their symptoms
• sources and nature of indoor allergens were not well understood,
advice offered on avoidance was often inadequate or even wrong

• The complexity and nonlinearity of dose response relationships also
makes such evaluations of the effectiveness of allergen avoidance
difficult


2001 : 29 trials (939 patients)

26 trials : physical
10 trials : chemical methods
8 trials : combination

Cochrane Library 2011, Issue 10

Cochrane Library 2011, Issue 10

• The variability applies to the evaluation of patients, the
intervention used, and the assessment of outcome

• Meta-analysis is only valid when the studies are
comparable, and this may not be true for the successful
studies on allergen avoidance
J Allergy Clin Immunol 2008;122:694-6

very different designs and engage different subjects, time
frames, controls, seasons, and methods of intervention
J Allergy Clin Immunol -

longer than 6 months


CURRENT MEDICAL GUIDELINES AND
ALLERGEN AVOIDANCE

• most professional guidelines for asthma management advocate the
avoidance of acute allergen „„triggers,‟‟

• there is a diversity of views about the role of allergen avoidance
practices in long-term disease management

• 2007 National Heart Lung and Blood Institute : EPR3 (US) report
– advises that the first and most important step in controlling
allergen induced asthma is to reduce exposure.


CURRENT MEDICAL GUIDELINES AND
ALLERGEN AVOIDANCE

• Finnish Allergy Program 2008-2018
– promotes holistic „„allergy health‟‟ through diet and physical
activity and advocates allergen avoidance only „„in mandatory
situations.‟‟

• Both the 2009 Global Initiative for Asthma and the British Thoracic
Society guidelines reflect (Cochrane review)
– no consistent evidence for allergen avoidance in preventing
asthma
– only tenuous evidence that reducing allergen exposure can
reduce asthma morbidity


ICON pediatric asthma
• some ambiguity with respect to the role of allergen avoidance

• JGCA, NAEPP3, and PRACTALL
– specific recommendations for the reduction in allergen exposure
for sensitized patients with asthma

• AAMH, GINA, and SIGN
– unproven effectiveness of current avoidance strategies on
asthma control

• a multifaceted, comprehensive approach is prerequisite for clinical
benefit

Allergy 2012; 67: 976–997

Cochrane Database of Systematic Reviews 2010, Issue 7.

House dust mite avoidance measures for
perennial allergic rhinitis
• 9 trials involving 501 participants
• 2 studies investigating the effectiveness of mite impermeable
bedding covers were of good quality
• 7 studies were small and of poor quality
• 2 trials investigated the efficacy of acaricides
• 2 trials investigated the role of high-efficiency particulate air (HEPA)
filters
• 1 trial, using a factorial design, investigated the efficacy of both
acaricide and house dust mite impermeable bedding covers in
isolation and combination
• Remaining 4 trials investigated the efficacy of bedroom
environmental control programmes involving use of house dust mite
impermeable bedding covers


House dust mite avoidance measures for
perennial allergic rhinitis
• Trials to date  small and of poor methodological quality
• difficult to offer any definitive recommendations on the role

• use of acaricides and extensive bedroom-based environmental
control programmes may be of some benefit in reducing rhinitis
symptoms  but the evidence is not strong
• Isolated use of house dust mite impermeable bedding is unlikely to
prove effective

• More research is needed


METHODS OF
MITE ALLERGEN AVOIDANCE

Method
• Physical method
– Encasing of bedding
– Vacuums cleaners
– Floor coverings
– Laundry
– Air filtration
• Chemical method
– Acaricide

Encasings
• In the bedroom, covering mattresses and pillows with impermeable
covers is effective
• This effect may be large, variable, and persist for a couple of months

• Encasings differ widely in their quality
– some cheap brands have large pores, other multilayered encasings
delaminate, and others harbor mites
• Tightly woven synthetic or cotton fabrics are preferred

• Most trials of encasings have failed to regularly wash them (difficult
with some encasings), which renders them ineffective as allergens
build up on the outer surface within several weeks

Curr Allergy Asthma Rep 2008;8:126-32

16 tightly woven:
9 United States
3 Japan
2 Thailand
1 Germany
1 France


laminate-coated and loosely woven cover molting among nonwoven fibers

dead mites on an acaricide-coated and nonwoven cover group of mites in the matrix of a nonwoven cover


Nonwoven easy access for mites to readily penetrate
into the substrate of the material

before after


tightly woven fabric with systematized regular fibers allowing little
space for penetration.

• Woven, nonwoven
– pore size between 2 and 10 um (average, 6 um)  blocking
most mite allergens

• Plastic
– pore free , best barrier in terms of blocking
– but the least comfortable : zero ventilation
– tendency to become a haven for mold spores

• For acaricide-coated materials
– pore size is usually not a major factor
– mites are eradicated on contact with the chemicals
– still allow the passage of allergens
– prevent penetration through the fabrics, but allow colonization


sponge-like polyurethane : lowest rate
Synthetic fibers and kapok mattresses : highest rate

Symptomatic level

Sensitized level

A combination of the following: choosing new sponge-
like polyurethane or coconut fiber mattresses with
mite-impermeable covers and washing sheets,
pillowcases, blankets, and mattresses pad at least
weekly in hot water should be the best method of
prevention in HDM allergen sensitive allergic patients Asian Pac J Allergy Immunol 2010;28:155-61

Laundry
• Both dust and cat and mite allergens are effectively removed by
laundry
– physical removal of both dust and mites by the multiple wash
and rinse cycles;
– effects of detergents additives
– subsequent drying procedures

• McDonald LG,Tovey E. *
– All mites were killed by water temperatures 55 degrees C or
greater
– Killing at lower temperatures was not enhanced by any of the
pure detergents or laundry products tested

* J Allergy Clin Immunol 1992;90:599-608

Floor coverings
• Designing the house with polished floors and wooden or
vinyl/leather furniture so as to limit the sites where mites can grow

• carpets fitted onto unventilated floors  water can accumulate 
growth of both fungi and mites

• hard floors are likely to be preferred as they are more easily kept in
a state that minimizes aeroallergen reaerosolization in the long term

• the little available data of aeroallergens in houses suggest that the
difference may be small and the effects complex


Vacuum cleaners
• Vacuum cleaners are heavily promoted

• Probably all cleaners cause a brief increase in personal
aeroallergen exposure under normal domestic conditions and high-
efficiency particulate arrest (HEPA) filters make little difference

• Thus, the benefits of HEPA filtration on exposure may have been
exaggerated and all cleaners probably provide a brief increase in
exposure.


Air management
• indoor relative humidity is kept below 50% (absolute humidity below
6 g/kg)

• In some areas of the world this can be done by increasing ventilation

• in other areas it is necessary to use air conditioning during the most
humid months of the summer


Air filtration
• The role of air filtration continues to be debated
• There is some consensus that small benefits exist, mainly for pet
allergens


Acaricides
• variety of acaricides have been used to treat carpets or furniture
• pyrethroids, natamycin (an antifungal), pirimiphos methyl, and
benzyl benzoate
• killing mites

• Acaricides proved largely ineffective because the mite populations
return shortly after their application and they may also cause skin
and respiratory irritation

• No data on clinical benefit exist, and concerns about human health
and environmental toxicity remain


Acaricides
• 1% or 3% tannic acid
– method of denaturing mite allergens
– reduction of mite allergen can be achieved,
– does not kill mites
– so the effect can only be temporary, approximately 6 weeks to 3
months

• may be recommended when it is not possible to remove the carpets
or change the furniture


Cockroach

• Biology And Characteristic

Cockroaches
• Phylum Arthropoda, class Insecta, order Blattaria
• major source of indoor allergens, especially in inner cities
• allergens can be derived from feces, saliva, or debris from dead
animals

• Most common species indoors:
􀂄 Blattella germanica, German
􀂄 Periplaneta americana, American

• World wide distribution
• Highest levels usually in kitchens (mite allergen :in bedding)


Cockroaches
• Allergens not easily detected in undisturbed air, large particles (like
dust mites) >10 μm in diameter, and that consequently fall rapidly

• Large quantities of cockroach allergens can accumulate in homes
and may remain for years after cockroaches have been eradicated

• it was the concentration of cockroach allergen in children‟s
bedrooms that correlated with the risk of hospitalization


American cockroach (Periplaneta americana)

German cockroach (Blattella germanica)

oriental cockroach (Blatta orientalis)

www.allergen.org
21/2/2013

Cockroach

• Avoidance Measures

Cockroach
• Pest allergens appear to be particularly difficult to eliminate and
require different strategies than those used for other indoor
allergens

• These interventions include initial removal of the insects, rodents, or
both but also require long-term care to prevent a return of the
infestation


Cockroaches
• effective when applied as part of an overall avoidance plan

The primary strategies are:
(1) poison bait
Bait for killing cockroaches ranges from boric acid, to a variety of chemicals including
hydramethylnon, abamectin, and fipronil
(2) careful housekeeping to enclose all sources of food for insects
(3) cleaning to remove any accumulated allergen
(4) sealing all possible access points to the house

• Spraying with insecticides
– is generally ineffective
– volatile organic substances used are often irritating to patients
with asthma


Cockroach
• Once cockroaches have been eliminated from the environment,
• a thorough cleaning is necessary
• not only immediately after pesticide treatment
• but continued for long periods of time (up to several months) to
remove the allergen


Pediatr Clin N Am ( ) –

Summary
• Many different allergens are found indoors, but dust mite, cat,
cockroach, mouse, and dog appear to be the most important
• single interventions for indoor allergens have limited effectiveness
• multifaceted, comprehensive approach is prerequisite for clinical
benefit
• Complete allergen avoidance is usually impractical, or impossible,
and often limiting to the patient
• some measures involve significant expense and inconvenience
• tailoring environmental interventions to specific sensitization profiles
has been shown to be of added value

It is also necessary to tailor interventions to an individual‟s living
situation and patterns of disease

House dust mites & cockroach biology & avoidance

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