What is a scabies mite? - briefly
The scabies mite is a microscopic, eight‑legged arachnid (Sarcoptes scabiei) that burrows into human skin to lay eggs, producing intense itching and a contagious rash. Transmission occurs through prolonged skin‑to‑skin contact.
What is a scabies mite? - in detail
The scabies organism is a microscopic arthropod belonging to the family Sarcoptidae. Adult females measure about 0.3–0.4 mm in length, roughly the size of a grain of sand, and possess a rounded body with short, stubby legs adapted for burrowing. Males are slightly smaller and lack the enlarged front legs used by females to dig tunnels in the skin.
Life cycle proceeds through six stages: egg, larva, protonymph, tritonymph, and adult. Eggs are laid within the epidermal burrows and hatch in 3–4 days. Larvae emerge with three pairs of legs, molt into protonymphs after 3–4 days, then into tritonymphs, and finally mature into adults within 10–14 days. The entire cycle can be completed in as little as three weeks under optimal conditions.
Transmission occurs primarily through prolonged skin‑to‑skin contact, allowing the female to deposit eggs directly into the host’s stratum corneum. Indirect spread via contaminated clothing, bedding, or towels is possible but less efficient, because the mite survives off the human body for only 24–36 hours.
Pathogenic effects result from the mite’s feeding activity and the host’s immune response. The female creates a serpentine tunnel approximately 1 mm long, where she deposits eggs and fecal pellets. Mechanical irritation from the burrow, combined with allergic sensitization to mite proteins, produces intense pruritus, especially at night. Secondary bacterial infection may develop if scratching breaches the skin barrier.
Diagnostic features include:
- Presence of characteristic burrows on wrists, interdigital spaces, elbows, or genitalia.
- Microscopic identification of mites, eggs, or feces from skin scrapings.
- Dermoscopic visualization of the “delta wing” sign, representing the anterior portion of a burrow.
Effective treatment requires topical acaricides such as permethrin 5 % cream applied from the neck down and left for 8–14 hours before washing. Oral ivermectin, dosed at 200 µg/kg, offers an alternative for widespread or refractory cases. All close contacts should receive simultaneous therapy to prevent re‑infestation.
Prevention focuses on minimizing prolonged direct contact with infected individuals, laundering clothing and bedding at ≥50 °C, and avoiding shared personal items. Environmental decontamination is less critical given the mite’s limited survival off the host.