House Dust MitesMitesMitesMitesMites.M.ppt

Mites

1. Asthma And House dust Asthma And House dust
mitesmites
Written by Dr. Ranya Saad
Modified by Dr. Shahira Ahmed

2. Objectives:Objectives:

Morphological characters of medically Morphological characters of medically
important mites causing asthmaimportant mites causing asthma

Rule of mite in inducing bronchial asthmaRule of mite in inducing bronchial asthma

3. Examples for Inhaled Allergens of Examples for Inhaled Allergens of
mitesmites
Dust mite (Dermatophagoides sp.)
92608A
dust mite
fecal pellet
Allergy is an exaggerated or hypersensitivity reaction of the immune
system to specific external substances called allergens, which are
usually harmless to most people.

4. 
People spent more than 75% of their time indoorPeople spent more than 75% of their time indoor

Dust Mites (Dermatophagoides
 pteronyssinus
Dust Mites (Dermatophagoides
 pteronyssinus
& D. farina) are the most common causes of & D. farina) are the most common causes of
allergy → Typical C/p of asthmaallergy → Typical C/p of asthma

50% of Children with Asthma are Sensitive to 50% of Children with Asthma are Sensitive to
House Dust Mite House Dust Mite

Increased exposure in early life, Increased Increased exposure in early life, Increased
likhood of sensitization to HDM by 2-7 years of likhood of sensitization to HDM by 2-7 years of
life.life.

5. Dust MitesDust Mites

Live in soft bedding such as pillows, carpet, Live in soft bedding such as pillows, carpet,
stuffed toys, fabric-covered furniturestuffed toys, fabric-covered furniture

Feed on skin scales shed by humans and Feed on skin scales shed by humans and
their petstheir pets

Mites and mite droppings can cause asthma Mites and mite droppings can cause asthma
and trigger existing oneand trigger existing one

6. Mites of medical importance:Mites of medical importance:
The most common dust mite species around the The most common dust mite species around the
world includeworld include
Dermatophagoides pteronyssinus(Dp), Dermatophagoides pteronyssinus(Dp),
Dermatophagoides farinae(Df), Dermatophagoides farinae(Df),
Euroglyphus maynei(Em) andEuroglyphus maynei(Em) and
Blomia tropicalis(Bt).Blomia tropicalis(Bt).
G.characters:G.characters:

Body regions consist of cephalothorax and Body regions consist of cephalothorax and
abdomen abdomen

No antennae, simple eyes.No antennae, simple eyes.

No wings, No wings,

4 pairs of legs. 4 pairs of legs.

7. Mites inducing asthma are the Dermatophagoides pteronyssinus, D.
farinae which usually account for 90 % of the mite species in house
dust.
Size: 0.1-0.6 mm
Have 8 legs

8. Life cycleLife cycle
The life cycle of house dust mites starts with the fertilized
female laying a couple of eggs per day .
Eggs hatch six-legged larvae
 Then shed their integuments and become eight-legged
resting protonymphs.
The protonymphs also shed their integuments and
become larger active tritonymphs.
Finally , the tritonymphs undergo another shedding of
skin developing into active adult mites

9. Incomplete metamorphosis:
There is no pupa stage in life cycle. The larvae is similar in
morphology and life habit with the adult, but the sexual organ still
undeveloped.

10. 
D. p is the dominant mite in constantly damp D. p is the dominant mite in constantly damp
climates (N. Europe)climates (N. Europe)

D. f survives better in drier climates D. f survives better in drier climates

Blomia tropicalis, commonly in tropical andBlomia tropicalis, commonly in tropical and
subtropical areas.subtropical areas.
Storage mites: in stored foods (Storage mites: in stored foods (‘baker’s itch’ or ‘baker’s itch’ or
‘grocer’s itch‘grocer’s itch).).
Geographical DistributionGeographical Distribution

11. PathogenesisPathogenesis

These microorganisms feed mainly from skin scales These microorganisms feed mainly from skin scales
shed by humans and their petsshed by humans and their pets

Exposure to house dust mite allergens may be a Exposure to house dust mite allergens may be a
primary cause or a risk factor in the development of primary cause or a risk factor in the development of
asthma.asthma.

Proteins found in the metabolic waste products Proteins found in the metabolic waste products
excreted in the feces by these microorganisms are excreted in the feces by these microorganisms are
the cause of the allergic reaction to them.the cause of the allergic reaction to them.

12. 
Allergenic molecules with enzymatic activity , Allergenic molecules with enzymatic activity ,
like like cysteine proteases (group1)cysteine proteases (group1), irritate the , irritate the
mucosal surface facilitating asthma process.mucosal surface facilitating asthma process.

One of the most studied allergens from this One of the most studied allergens from this
groupgroup, , Der p 1 Der p 1 working through:working through:
oIncreasing the permeability of the respiratory Increasing the permeability of the respiratory
mucosamucosa
oEnhancing antigen processingEnhancing antigen processing
oPromoting IgE synthesisPromoting IgE synthesis
oAugmenting TH2 cell responsesAugmenting TH2 cell responses

13. Enzymatic Activity of Some Allergens Enables Easy Enzymatic Activity of Some Allergens Enables Easy
Penetration of Epithelial Cell BarriersPenetration of Epithelial Cell Barriers
The cysteine protease Der p 1 is from fecal pellets of house dust mite.
Protease inhibitors may be a novel therapeutic approach for allergies.

14. Examples for Positive dermal skin prick Examples for Positive dermal skin prick
testtest

15. Thank youThank you