House Dust Mites & Allergy. Jeffrey D. Miller, MD

House Dust Mites
and
Allergy
Jeffrey D. Miller MD
Assistant Clinical Professor of Pediatrics,
New York Medical College
© Mission: Allergy, Inc.

Dust mites:
• Dust mites are not insects. They are arachnids, microscopic
relatives of spiders and ticks.
• Unlike insects, adult mites have 8 legs, not 6, and do not have
segmented bodies.
House Dust Mites & Allergy © Mission: Allergy, Inc.

D. pteronyssinus dust mite seen through an electron microscope.

Side view of a dust mite seen through an electron microscope.

Adult dust mites:
• Adult dust mites are approximately 1/100 of an inch (1/3 of a
millimeter or 330 microns) in length, a size at the threshold of
visibility with the naked eye.
• Although this is extremely small for a multi-cellular organism,
it is large for a micro-organism. Bacteria, for example, are
about 100 times smaller.

Adult mite shown with size scale
(100 microns = 1/10 millimeter = 4/1000 inch)

Dust mites under a microscope:
• Dust mites are therefore easily seen through a low-
power (15-80X) microscope. By comparison, bacteria
are viewed under 1,000X magnification.
• Dust mites appear watery and translucent under a
regular microscope.

D. pteronyssinus dust mite seen through a low-power microscope.

Dust mites under an electron microscope:
• A much higher-powered electron microscope is required to
see fine detail, such as the fingerprint-like ridges in the dust
mite’s outer covering, but gives the false impression that dust
mites are grey and hard.

Close-up of dust mite showing surface ridges
Electron microscope view

Dust mites require humidity to survive:
• Dust mites require at least 50% relative humidity to survive.
The ideal relative humidity for mite growth is 75%.
• Dust mites absorb water vapor from the air by specialized
tear-shaped organs called “supra-coxal glands”, present at the
base of the first set of legs.
• These glands cannot absorb water vapor if the relative
humidity of the air remains below 50%, in which case the mite
will become dehydrated and die.

Specialized tear-shaped glands absorb water vapor from the air.

Dust mites and light:
• Dust mites have feelers (“setae”) on their body and legs,
which allow them to sense their environment.
• Although they have no eyes, dust mites are light sensitive,
and move away from the light.
• For that reason, dust mites are not living on hard exposed
surfaces, but rather are burrowed into the dark recesses of
soft materials, such as pillows, mattresses, blankets, carpets,
upholstered furniture, clothing, and stuffed toys.

Whisker-like feelers called “setae” on the mite’s body and legs.

Dust mites have specialized feet:
• Specialized “feet” allow the mite to maintain a strong, suction
cup like grip.
• Note the setae around the foot in the following photo….

Close-up of a dust mite foot.

Dust mites have sticky feet:
• These sticky feet allow dust mites to hold onto the fibers in
bedding, clothing and carpeting.
• That is why very few live dust mites can be removed by a
vacuum cleaner.

House dust mite walking on a fiber within a pillow.

Dust mite digestion:
• Mites ingest food through a mouth at their front…

Close-up of dust mite mouthparts.

Dust mite digestion:
• …and excrete waste through an anal slit in the back.

The dust mite’s rear end.

Dust mite reproduction:
• Dust mites reproduce sexually.
• If you were a male dust mite, you might find the following
female mite attractive.

Bottom view of a female dust mite.

• Dust mites are so tiny that the sperm cells must exit single
file!
• Mating dust mites thus stay attached for about three hours.
Just imagine!

Parental Advisory: This is not one mite with 2 heads

• A female dust mite lays about 60 eggs during her 80-day
lifetime.
• Given adequate food supplies and humidity, dust mites can
thus become plentiful rather quickly.

Dust mite eggs
low power microscope view
eggs


Dust mite eggs:
• The oval eggs appear clear and translucent when viewed
under the light microscope…

A cluster of dust mite eggs
low power microscope view, black background

Dust mite eggs:
• ...but appear solid when viewed through an electron
microscope.
• (The small spheres adhering to the right side of the egg in the
following image are fecal waste particles.)

Dust mite egg
high magnification view

Dust mite eggs:
• The eggs hatch, leaving behind an empty shell.

Cluster of dust mite eggs, with one hatched.

Dust mite larvae:
• In the following photo, a 6-legged larva has emerged from the
egg.
• It is about the same size as the egg.

Dust mite larval stage.
larva

Dust mite nymphs:
• The dust mite larva sequentially matures into the 1st stage
nymph (“protonymph”) and the 2nd stage nymph
(“tritonymph”).
• The last stage nymph matures into an adult.

Adult and nymph dust mites.

Dust mite growth:
• Just as a lobster must molt its external skeleton in order to
grow, each dust mite larval and nymph stage must shed its
external skeleton (“exoskeleton”) before growing to the next
stage.

Shed dust mite exoskeletons (in brackets)
low-power light microscope



Dust mite exoskeletons:
• In the following photo, you can see on the left side of this
shed exoskeleton where the mouth and forelegs used to be.
• It is as if the mite unzipped its outer suit and left it behind.
The body area is now hollow.

Shed Exoskeleton
Shed mite exoskeleton.

Dust mite allergy:
• But for the allergy sufferer, the mite fecal particle is the star of
the show, and the main villain.
• Allergic reactions to dust mite waste particles are the most
common cause of nasal allergy, allergic asthma, and allergic
eczema (atopic dermatitis).

Mite
poop
Mites excrete solid waste particles—the main cause of dust
mite allergy.

Dust mite waste particles:
• A single house dust mite can produce 1,000 waste particles
during its 3-month lifetime.
• Mite waste particles are surrounded by a membrane
containing digestive enzymes, which continue to digest
nutrients after the fecal particle has been expelled.
• Under some circumstances, mites eat their own feces (ugh),
allowing them to absorb additional nutrients that have been
digested by those enzymes outside of the mite’s body.

Mite feces
Mite fecal particles.

Mite waste particles become airborne:
• The waste particles’ weight and size are such that they
become airborne when the material in which they are
present is disturbed, for example when making a bed, putting
one’s face on a pillow, walking on a carpet, putting on a
sweater, or hugging a stuffed toy.
• Without further disturbance, the particles settle to the floor
within 20-30 minutes.
• Mite waste particles are the same size as pollen grains. When
airborne, dust mite waste particles can contact the skin and
are easily inhaled into the nose and bronchial tubes.

Mite poop
The mite waste particle—the main cause of dust mite allergy.

Dust mites and allergens:
• The digestive enzymes surrounding the fecal particles are
some of the main allergy-causing substances (“allergens”) in
dust mites, capable of triggering allergic reactions in the
eyes, nose, bronchial tubes, and skin of sensitive individuals.
• Apart from releasing histamine and other inflammatory
chemicals as part of the allergic reaction, these protein-
splitting enzymes also directly break the tight bonds
between cells in the nose and respiratory tract, cause
asthmatic changes in the muscles of the bronchial tubes, and
cause skin disruption and itch in eczema.

Close-up of mite poop.

Dust mite waste particles (feces):
• Mite feces also contain bacterial substances that the body
recognizes as belonging to primitive organisms, and which
therefore provoke immunological reactions.
• These substances include bacterial DNA and “endotoxin”.

House dust mite with allergy-causing fecal particles.

Dust mite exoskeletons are allergens:
• Although mite fecal particles are the main source of dust mite
allergens, shed exoskeletons and the body fragments of dead
dust mites also contain allergen and other substances that
stimulate the immune system.
• One of these substances is “chitin”, which is also present in
the outer coverings of insects, shellfish, fungi and parasitic
intestinal worms—and which the immune system
immediately recognizes as coming from a potential invader.

Shed Exoskeleton
Mite feces
Mite fecal particles and shed mite exoskeleton.

The perfect allergen delivery system:
• So unfortunately for us humans, the dust mite seems to have
evolved the perfect allergen delivery system: particles the
right size to become airborne and be inhaled, containing not
only strong allergens but also protein-splitting enzymes,
bacterial products, and chitin—all of which provoke
immunologic and allergic reactions.

The perfect allergen delivery system.

WARNING: Looking at too many pictures of dust mites can lead
to a condition where everything starts to look like a dust mite.

I think that is happening to me!

missionallergy.com
Toll Free: 1-877-NOALLER(GY) • 1-877-662-5537

House Dust Mites & Allergy. Jeffrey D. Miller, MD

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to House Dust Mites & Allergy. Jeffrey D. Miller, MD

Similar to House Dust Mites & Allergy. Jeffrey D. Miller, MD (20)

Recently uploaded

Recently uploaded (20)

House Dust Mites & Allergy. Jeffrey D. Miller, MD

Editor's Notes