General morphology and biology
The body of acariform mites lacks pronounced segmentation and is divided into two regions: the gnathosoma (head region with mouthparts) and the idiosoma (fusion of all other body parts). Depending on the group, the mouthparts can be of chewing, biting, or sucking type and consist of chelicerae, pedipalps, and labrum.
The respiratory system in mites may be absent (in which case they breathe through the integument) or represented by tracheae with stigmata. The alimentary canal consists of foregut, midgut (with diverticula), and hindgut. The nervous system is highly concentrated—ganglia merge into a single mass around the esophagus.
Development occurs with incomplete metamorphosis: a six-legged larva hatches from the egg, which after molting turns into an eight-legged nymph (there may be several stages), and then into an imago.
Itch mite (Sarcoptes scabiei)
Belongs to the suborder Sarcoptiformes (Sarcoptiformes). This is a small, rounded mite up to 0.4 mm in length. The integument features fine striation and is covered with scales and posteriorly directed setae. Mouthparts are of the biting type, legs are short, ending in suckers or setae. Respiration is cutaneous.
Sarcoptes scabiei is the causative agent of scabies. Infection occurs through contact with an infected person or via fomites. Females burrow tunnels in the epidermis (especially in areas with thin skin: interdigital folds, elbows, abdomen) where they lay eggs and deposit feces. The movement of the mite causes intense nocturnal itching, and scratching can lead to secondary infections (dermatitis, furunculosis). The development cycle from egg to imago takes 10–14 days.
Chigger mites
Belong to the suborder Trombidiformes (Trombidiformes). They are characterized by larval parasitism: only the larvae parasitize animals and humans, while nymphs and imagos are free-living predators. The larvae are red or orange in color and have sucking mouthparts; they feed on tissue fluid rather than blood.
Massive attacks by larvae cause trombiculiasis (autumn erythema), accompanied by severe itching. The main epidemiological hazard of chiggers is that they are specific vectors of Orientia tsutsugamushi — the causative agent of tsutsugamushi fever (scrub typhus). They can also serve as a natural reservoir for other infections, including HFRS and toxoplasmosis.
Hair follicle mite (Demodex folliculorum)
Also belongs to trombidiform mites. This is a very small (about 0.3 mm) worm-shaped mite.
Demodex folliculorum inhabits sebaceous glands and hair follicles on the face, ears, and abdomen. Carriage is often asymptomatic, but with a massive accumulation of mites, inflammation and blockage of the glands develop — a condition known as demodicosis. The infection is transmitted by contact from person to person. Parasitism can last for decades and is difficult to treat.
Briefly: answers to topical questions
What pharmacological agents are used for etiotropic treatment of scabies?
Aerosol preparations and benzyl benzoate suspension are used for the treatment of scabies.
- Aerosol preparations — applied once from top to bottom from a distance of 20–30 cm, repeated application is performed on the 4th day to destroy hatched larvae.
- Benzyl benzoate suspension — a 20% water-soap suspension is used for adults and 10% for children. The total course is 6 days, however, the application of the product is carried out exclusively on the 1st and 4th days.
To remember the number of legs at different stages, keep in mind: the larva has as many legs as an insect (6), while the nymph and imago have as many as a spider (8).
Class and exam questions
Can you catch scabies from a dog or a cat?
Animals have their own specific species of scabies mites. Upon close contact, they can transfer to humans, causing "pseudoscabies", but they do not survive long on a non-specific host.
What do chigger mites feed on when on humans?
Parasitic chigger larvae feed on tissue fluid, not blood. After engorgement, they drop off into the soil.
What is the difference between sarcoptiform and trombidiform mites?
Sarcoptiform mites (e.g., the itch mite) have biting or chewing mouthparts, whereas trombidiform mites (chiggers, follicle mites) have sucking mouthparts.
What else to study on this topic
- Sense organs of acariform mites: trichobothria, solenidia, tactile setae.
- Structural features of the reproductive system and reproduction in mites.
- Stored-product mites: the family Acaridae and their significance.
- Prevention of scabies and treatment of clothing and linens.
- Mechanisms of transmission of tsutsugamushi fever in natural foci.
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