Scabies

Scabies is one of the commonest dermatological conditions, accounting for a substantial proportion of skin disease in many low- and middle-income countries. Globally, it is estimated to affect more than 200 million people at any time and more than 400 million people every year.

Scabies is caused by infestation of the skin with a microscopic mite (Sarcoptes scabiei var. hominis) characterized by itch and a skin eruption. Scabies is frequently complicated by bacterial skin infection (impetigo). In turn, impetigo may result in abscesses, sepsis and invasive infections with bacteria, most frequently Staphylococcus aureus and Streptococcus pyogenes, the latter of which may result in kidney disease and rheumatic heart disease. Scabies also impacts quality of life: itch and visible rash often lead to poor sleep, stigmatization and social exclusion, interrupting school and work attendance.

Scabies affects the world’s most disadvantaged populations, especially people living in crowded and impoverished conditions, from island communities in the Pacific to favelas of Latin America, remote and rural communities across Africa and Australia, and displaced populations living in camps. In resource-poor settings, scabies and its complications impose a major cost on health care systems. In high-income countries, cases are sporadic, yet outbreaks in health institutions and vulnerable communities contribute to significant economic costs for national health services.

Scabies mites burrow under the upper layer of the skin to lay their eggs, resulting in intense itching. Characteristics of scabies are papules or burrows in typical locations, including the web spaces of the fingers and toes, wrists, buttocks, breasts in females, and genitals. In young children and the elderly, scabies lesions may also be present on the palms, soles and scalp. The itching and rash cause poor sleep, stigmatization and social exclusion, as well as absenteeism from education and employment, resulting in reduced learning potential for children and economic impacts for families and communities. Presence of redness, pus or crusts may indicate a secondary bacterial infection. This should be differentiated from crusted scabies, a severe form of scabies, that is characterized by thick, scaly, plaques over the skin and, in severe cases, deep fissures.

 

Primary management of affected individuals involves application of a topical scabicide such as 5% permethrin, 0.5% malathion in aqueous base, 10–25% benzyl benzoate emulsion or 5–10% sulfur ointment. Oral ivermectin is also highly effective and is approved in several countries. The safety of ivermectin in pregnant women or children below

15 kg body weight has not been established, so ivermectin should not be used in these groups until more safety data are available. Itch commonly intensifies with effective treatment for 1–2 weeks and treated individuals should be informed accordingly.

Because people in the early stage of new infestation may be asymptomatic, it is critical to treat the whole household at the same time as the diagnosed case. Repeating treatment in the time frame appropriate for the chosen medication (typically after 7–14 days) will lead to a higher efficacy, particularly for oral ivermectin, which does not kill mite eggs.