Scabies

Notification requirement for scabies

Notification is not required.

Primary school and children’s services centres exclusion for scabies

Exclude until the day after appropriate treatment has commenced.

Infectious agent of scabies

The Sarcoptes scabiei mite is a tiny eight-legged creature that is barely visible to the naked eye. Females are 0.3–0.4 mm long and 0.25–0.35 mm wide. Males are less than half the size of the female.

Scabies life cycle

The mite undergoes four stages in its life cycle: egg, larva, nymph and adult. The female mite burrows into the skin and lays eggs. Eggs hatch after 2–3 days, and larvae travel to the skin surface, where they moult into nymphs and become adult mites. The period from fertilisation to adult mite ranges from 10 to 15 days. Female mites live for about 2 months, lay three eggs a day and can travel up to 3 cm per minute.

Identification of scabies

Clinical features

Scabies is a highly contagious parasitic skin infestation, characterised by thin, slightly elevated, wavy grey–white burrows that contain the mites and eggs. Multiple papules and vesicles soon appear.

The most common sites for burrows are between the fingers and toes, anterior surfaces of the wrists and elbows, axillae, lower abdomen, beneath breasts and genitalia. The face, head, palms and soles are seldom involved in adults. In infants, the elderly and immunosuppressed people, any area of skin may be infested.

Nodular scabies results from an exaggerated hypersensitivity reaction, and is characterised by chronic, pruritic nodules that are often localised to the axilla, groin and genitalia.

Itching varies from person to person but may be severe. It tends to be more marked at night or following a hot bath. Scratching may lead to secondary bacterial infections.

Crusted (Norwegian) scabies

This is a particularly virulent infestation that can occur in elderly, debilitated or immunosuppressed patients, including those with HIV infection. These patients are highly infectious and difficult to treat. Large areas of the body may appear scaly and crusted, with thousands of mites and eggs. Topical treatments may not penetrate the crusted, thickened skin, leading to treatment failure.

Crusted scabies may be misdiagnosed as psoriasis or eczema.

Diagnosis

Diagnosis is commonly made clinically by examining the burrows or rash. The diagnosis may be confirmed by scraping the burrows with a needle or scalpel blade, and identifying the mites or eggs under a microscope. A negative result on skin scraping is not always conclusive, as the infested person may have few mites (on average 10–15), and these can easily be missed on skin scraping. In atypical cases, biopsy may help confirm the diagnosis.

Incubation period of scabies

It may take 2–6 weeks before itching occurs in a person not previously exposed to scabies.

Symptoms develop much more quickly if a person is re-exposed, often within 1–4 days.

The incubation period may be shorter if infestation is acquired from a person with crusted (Norwegian) scabies. In this case, it is between 10 and 14 days.

Public health significance and occurrence of scabies

Scabies occurs worldwide regardless of age, sex, race, socioeconomic status or standards of personal hygiene.

Cyclical epidemics occur at intervals of 10–15 years.

Outbreaks may occur in childcare centres and kindergartens, and are frequently reported in nursing homes and institutions. Scabies is more likely to spread in situations of overcrowding.

Superinfections secondary to crusted (Norwegian) scabies are more prevalent among high-risk groups, and therefore affected patients should be screened for HIV and/or HTLV-1 infection.

Reservoir for scabies

Humans are the primary reservoir. Other species of mite from animals or birds can also live on humans but do not reproduce in the skin.

Mode of transmission of scabies

Scabies is transmitted:

• primarily via skin contact with an infected person (e.g. sex partners, children playing, healthcare providers)
• less commonly via contact with towels, bedclothes and undergarments, if these have been contaminated by infested people within the previous 4–5 days.

The mites cannot jump or fly. Adult scabies mites may survive off the skin for up to 48 hours under room conditions.

Period of communicability of scabies

Scabies is communicable until mites and eggs are destroyed by treatment, usually two courses 1 week apart. Itching may persist for 2 or more weeks after successful eradication of the mite.

Susceptibility and resistance to scabies

Fewer mites succeed in establishing themselves in people previously infested than in those with no previous exposure. Diminished resistance to infestation is also suggested by the observation that immunologically compromised people are most susceptible to severe infestations.

Control measures for scabies

Preventive measures

Educate the public about the mode of spread, and early diagnosis and treatment, and promote good personal hygiene.

Control of case

For simple scabies, the usual treatment is permethrin applied topically to the whole body, including face and hair (avoid eyes and mucous membranes), and left overnight, or benzyl benzoate 25 per cent emulsion applied topically, including face and hair (avoid eyes and mucous membranes), and left for 24 hours. This should be repeated after 7–14 days.

For children less than 2 months of age, sulfur 5 per cent cream or crotamiton 10 per cent cream are alternatives (see the current edition of Therapeutic guidelines: antibiotic).

For crusted (Norwegian) scabies, the addition of oral ivermectin 200 µg/kg followed by additional doses is suggested, depending on the severity of the infestation. Ivermectin therapy may also be applicable to patients unable to comply with topical administration. For Norwegian scabies, seek specialist infectious diseases or dermatological advice. With ivermectin therapy, caution should be taken in pregnancy and children less than 5 years of age.

Infested people should be excluded from school or the workplace until the day following the first application of appropriate treatment.

For hospitalised patients or patients in nursing homes, contact isolation should be used until appropriate treatment has commenced. To prevent nosocomial infection, affected staff should be excluded until appropriate treatment has commenced.

Control of contacts

Investigate contacts and the source of infestation.

Simultaneously treat all household contacts, sexual contacts, and those considered ‘at risk’ by virtue of close contact in nursing homes and institutions.

Control of environment

Clothing, towels and bedclothes used by the infested person in the 48 hours before treatment should be laundered using the hot cycle, or drycleaned. Alternatively, items may be placed in a plastic bag and sealed for 1 week before laundering, as the mite cannot survive lengthy periods off the human body.

Outbreak measures for scabies

Special settings

School and childcare facilities

Exclude the case until the day after appropriate treatment has been given.

Advise staff and parents of other children who may have had direct contact with the infested person and may require treatment. Treat all those who have had close skin-to-skin contact with the case. This includes family members, playmates and staff. Treatment should occur simultaneously to reduce the risk of re-infestation. Generally, prolonged close contact is required for transmission.

Nursing homes, aged care and other residential facilities

See 'Guidelines for the control of scabies’.