Mites

Belong to subclass Acari, class Arachnida
Small: <1 mm in length
Body is unsegmented and sac-like, with no clear separation of cephalothorax and abdomen
Larvae: 6 legs; Nymphs/Adults: 8 legs

What are the distinguishing characteristics of mites?

egg → larva → nymph → adult

Lifecycle

project forward or downward, used for biting, piercing, or sucking

Mouthparts (gnathosoma)

Order Acariformes

Includes: Sarcoptiformes, Trombidiformes
Contains most medically important mites (e.g., scabies)

Order Parasitiformes

Mainly ticks, but some parasitic mites like Dermanyssus and Ornithonyssus

Causes scabies
Obligate parasite; burrows into skin
Transmission: direct skin-to-skin contact
Female mites dig burrows and lay eggs
Clinical signs: intense pruritus (especially at night), burrows, rash, nodules
Severe form: Norwegian scabies (crusted scabies) in immunocompromised individuals

What are key features and clinical manifestations of Sarcoptes scabiei?

Female lays eggs in skin burrows
Eggs hatch into larvae (3 pairs of legs)
Larvae develop into nymphs and adults (4 pairs of legs)
Life cycle completed in 10–17 days

Describe the life cycle of Sarcoptes scabiei.

Clinical signs: pruritic papules, burrows, distribution pattern
Microscopy: skin scraping with mineral oil, examined for mites, eggs, fecal pellets
Dermatoscopy: visualization of burrows

How is scabies diagnosed?

Topical Permethrin 5% cream (first-line)
Oral ivermectin (for crusted or refractory cases)
Treat close contacts
Wash clothing/bedding in hot water

What are common treatments for scabies?

Commensals on human skin; live in hair follicles and sebaceous glands
Two species: Demodex folliculorum and Demodex brevis
Associated with rosacea, blepharitis
Higher burden in immunosuppressed individuals
Diagnosis: skin scraping or tape test, microscopy

What are the characteristics of Demodex mites?

Only larval stage is parasitic
Inject enzymes that digest host tissue, forming a stylostome
Cause intense pruritus and dermatitis
Vectors of scrub typhus (Orientia tsutsugamushi) in Asia-Pacific region

What are chiggers and how do they affect humans?

Parasitizes insect larvae in stored grain
Human exposure through contaminated materials
Causes intense itching, dermatitis, possible vesicles
Nonburrowing; reaction is to mite toxin

What is the significance of Pyemotes tritici?

Species: Dermatophagoides pteronyssinus and D. farinae
Found in bedding, carpets, and furniture
Fecal particles and exoskeletons are potent allergens
Linked to asthma, rhinitis, and eczema

What role do house dust mites play in allergic disease?

Mites that thrive in organic matter (e.g., molds, fungi)
Includes: grain mites, cheese mites
Cause occupational dermatitis (e.g., grocer’s itch)

What are organophilic mites?