Scabies

Definition

Scabies is a highly contagious skin infestation caused by the mite *Sarcoptes scabiei var. hominis*, characterized by intense pruritus, especially at night, and a papular or vesicular rash.

Epidemiology

• Affects all age groups worldwide; more common in crowded living conditions.
• High prevalence in children, elderly, and immunocompromised individuals.
• Outbreaks are common in nursing homes, schools, and prisons.
• Incidence is higher in tropical and subtropical regions.
• Crusted (Norwegian) scabies occurs in immunocompromised patients and is highly infectious.

Etiology

• Caused by infestation with the mite *Sarcoptes scabiei*.
• Transmitted primarily by prolonged direct skin-to-skin contact; rarely via fomites in crusted scabies.
• Risk factors: overcrowding, poor hygiene, immunosuppression, institutional settings.
• Secondary bacterial infection may occur due to scratching.

Pathophysiology

• Female mites burrow into the stratum corneum of the epidermis, laying eggs.
• Immune response to mite antigens and feces triggers intense pruritus and inflammation.
• Burrows appear as linear or S-shaped tracks on the skin.
• Scratching can cause excoriations and secondary bacterial infection (commonly *Staphylococcus aureus* or *Streptococcus pyogenes*).
• In crusted scabies, there is hyperinfestation with thick crusts containing thousands of mites.