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Scabies is caused by skin infestation with the mite Sarcoptes scabiei which is an arthropod (member of the class Arachnida). Like many other infectious diseases, it is transmitted by contact (McCarthy, “Scabies: more than just an irritation” (2003). Poverty and overcorwding are often concomitant. However, scabies is not influenced by hygiene practices or the availability of water.
Life Cycle: The lifecycle of S scabiei begins with the mating of adult male and female mites, after which the adult male dies, while the female beings to lay eggs in the skin buttrow for her lifespan of 4-6 weeks. After 3-4 days the eggs hatch and six legged larvae cut through the roof of the burrow to reach the skin surface. They then dig burrows and pass through two further developmental stages before multing into either males or females.
Symptoms: Classical scabies presents as an intesnely pruirtic rash, particularly involving those region of the skin best suited for the mite, such as the interditial web spaces, wrists, anterior axilary folds, periumbilical skin, pelvic girdle including buttocks, ankles, the penis and the perioreolar region in femails. . Onset of these symptoms in a host with no prior infestation occurs after 3-4 weeks. Patients complain that the pruritis is more intense at night.
Diagnosis: can be made based on a typical history of pruritis, worse at night and the distribution of inflammatory papules. Confirmation can be made by gently scraping the skin off the burrow with a lunt scalpel blade, and placing the material on a glass slide with a drop of 10% potassium hydroxide or minieral oil, and seeking mites, eggs by low power microscopy.
Treatment: Permethrin 5% Lyclear) is considered the treatment of choice in the US.