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Dermatophagoides and Blomia tropicalis

  • Parasite
  • Exam priority: medium

Microscopic mites in mattresses, pillows and carpets that eat skin flakes. Their droppings are a leading cause of allergic asthma and rhinitis.

Updated

Also called: house-dust mites, ácaros del polvo

Quick facts

Type
Parasite · Ectoparasites
Gram / shape
Oval
Spread
Not an infection · Shaking bedding · Humid
Causes
Allergic asthma · Allergic rhinitis and conjunctivitis
Treatment
Reducing allergen exposure

At a glance

Shape
Oval, creamy white body with 8 legs, invisible to the naked eye
Family
Pyroglyphidae (Dermatophagoides pteronyssinus, D. farinae); Echimyopodidae (Blomia tropicalis)
Type
Free-living mites (arachnids); not parasites, but a major source of indoor allergens
Size
About 0.2–0.4 mm

Morphology

  • No eyes; they absorb water from humid air through the body surface.
  • They feed on human and pet skin flakes softened by moulds.
  • The allergens are in faecal pellets and body fragments, which settle in dust rather than staying in the air.

Transmission

  • Not an infection: people are exposed by breathing allergens in dust, mostly in bed while sleeping.
  • Shaking bedding, sweeping or dusting lifts the particles briefly into the air.
  • Humid, warm climates such as Colombian lowlands and the Caribbean coast favour large mite populations all year.

Reservoir: Mattresses, pillows, upholstered furniture, carpets, curtains and stuffed toys; Stored grain and food (some related storage mites)

Isolation precautions

What the care team adds to standard precautions.

  • Standard

Life cycle

  1. The female lays eggs in dust where skin flakes collect, such as mattresses.
  2. A six-legged larva hatches and feeds on skin scales.
  3. It goes through two nymph stages with eight legs before becoming an adult.
  4. Egg to adult takes about one month in warm, humid conditions; adults live a few months.
  5. Below about 50% relative humidity mites dry out and populations fall.

Virulence factors

  • Mite allergens include enzymes that damage the airway lining and promote allergic (type 2) inflammation.
  • Tropomyosin from mites cross-reacts with that of shrimp and Ascaris, which can link food allergy, helminths and asthma.
  • Sensitisation in early life is a strong risk factor for asthma in children.

Diseases it causes

Clinical picture

  • Perennial sneezing, nasal blockage and itchy eyes, worse at night and on waking.
  • Asthma with cough and wheeze in sensitised children and adults.
  • Symptoms often worsen when making beds, cleaning or in old, closed rooms.

Diagnosis

  • Skin prick tests with D. pteronyssinus, D. farinae and, in the tropics, B. tropicalis extracts.
  • Specific IgE in serum; molecular tests for single allergens help choose immunotherapy.
  • A positive test means sensitisation; it matters only if it matches the symptoms.

Treatment

Reducing allergen exposure, plus standard treatment of rhinitis and asthma: intranasal corticosteroids, antihistamines, inhaled corticosteroids and leukotriene antagonists. Allergen immunotherapy with mite extracts can change the course of the allergy in selected patients.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

Prevention

  • Allergen-proof covers for mattresses and pillows.
  • Wash bedding every week in hot water.
  • Keep indoor humidity below about 50% and ventilate rooms.
  • Fewer carpets, curtains and stuffed toys in the bedroom; damp dusting and vacuums with high-efficiency filters.

Test yourself

Think of the answer, then tap the question to see it.

Which part of the house-dust mite carries most of the allergen?

Its faecal pellets and body fragments, which settle in bedding, carpets and furniture.

Which environmental factor most controls mite populations?

Humidity: mites dry out and decline when indoor relative humidity stays below about 50%.

Which tropical mite should be included in skin tests in Colombia?

Blomia tropicalis, together with Dermatophagoides pteronyssinus and D. farinae.

Why can mite allergy relate to Ascaris and shrimp?

Because their tropomyosins are similar and IgE against one can cross-react with the others.

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Connections

← Back to the group: Ectoparasites

Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: Dust Mites | American Lung Association (American Lung Association, 2024); Dust Mites and Cockroaches | National Institute of Environmental Health Sciences (NIEHS (NIH), 2025); IgE responses to Ascaris and mite tropomyosins are risk factors for asthma (Clinical and Experimental Allergy (record at Pontificia Universidad Javeriana), 2015); Allergic rhinitis: MedlinePlus Medical Encyclopedia (MedlinePlus (NLM), 2024).

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Representative model, for educational purposes only.