Scabies is a common infestation by a mite Sarcoptes scabiei. According to Chosidow, It occurs in both sexes, all age groups, all ethnic groups and in every socioeconomic level. According to Caumes, scabies is the most common cause of generalized pruritus in travelers. It is highly contagious and transmitted by skin to skin contact. It is estimated that the worldwide prevalence of scabies is 300 million cases yearly.
Location of scabies rash
At the site of the bite of the mite are telltale burrows, especially at the flexor surfaces of the wrists, between fingers, on knees, elbows and the penis. In adults, the face, scalp, neck, palms and soles are not involved. The female mite lays eggs. Larvae hatch 2 to 3 days after the eggs are laid and move to the skin surface.
Characteristics
The rash of scabies is due to both infestation and a hypersensitivity reaction to the mite; it consists of papules, nodular lumps or bumps (often on the penis and scrotum) and may spread where burrowing has not occurred as the mite's feces cause itching and skin irritation, which increases at night and after a hot shower. The constant scratching causes sores on the body and these sores may ooze or become infected and be a breeding ground for bacteria. In more advanced cases, the skin becomes crusty and scaly.
For a person who has never been infected (primary exposure) pruritus may manifest after a period of 4 to 6 weeks. A person previously infected (secondary exposure) may experience a severe itch within a few days; a treatment done once does not guarantee immunity.
Transmission
Transfer of mites from person to person can occur by shaking hands or having sex and is aided by crowded conditions, uncleanliness and multiple sexual partners. Outbreaks can occur in institutions, including hospitals and nursing homes.
Diagnosis
The diagnosis is based on the history and physical examination of the patient, as well as the customary appearance and distribution of the the rash and the presence of burrows.
Tests
Whenever possible, definitive diagnosis should be made based on unroofing burrows with a scalpel and examining the skin scrapings with a microscope using low power and looking for a mite, its eggs and excreta. Failure to find a mite does not rule out the diagnosis.
Treatment
According to a CDC fact sheet, permethrin 5% is recommended as standard therapy, with crotamiton or oral ivermectin as alternatives. Topical permethrin must be applied from the top of the neck to the soles of the feet and left overnight, then washed by taking a bath or shower. Itching can persist up to 4 weeks after scabicide treatment. Importantly all clothes, bedding and towels used by the infested person must be washed in hot water and dried at a high temperature to kill any remaining mites/eggs. Household contacts must be treated simultaneously to prevent the spread of the infestation.
References
- Chosidow O. NEJM 354 (2006): 1717-27.
- Caumes E., et. al., Clin Infect Dis 1995: 20:542-548.
- Scabies fact sheet. Atlanta: Centers for Disease Control and prevention, November 10, 2008
