Scabies

Victorian statutory requirement

Notification is not required.

School exclusion: exclude until the day after appropriate treatment has commenced.

Infectious agent

The Sarcoptes scabiei mite is a tiny eight legged creature barely visible to the naked eye. Females are 0.3 to 0.4mm long and 0.25 to 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, lays eggs, larvae travel to the skin surface where they moult into nymphs and become adult mites. The period from fertilization to adult mite ranges from 10 to 14 days. Female mites live about two months, laying three eggs a day and travel up to three centimetres a minute.

Identification

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 female breasts and genitalia. The face, head, palms and soles are seldom involved in adults but in infants any area of skin may be infected.

Immunosuppressed people, those living in institutions and the elderly may also show a clinical pattern of infestation similar to that in infants.

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

Crusted (Norwegian) scabies
This is a particularly virulent infestation that can occur in the elderly, debilitated or immunosuppressed patients including those with HIV infection. These patients are highly infective and difficult to treat. Large areas of the body may appear scaly and crusted with thousands of mites and eggs. Treatment applied directly to the skin such as creams and lotions may not penetrate the crusted thickened skin and result in treatment failure.

Crusted scabies may be misdiagnosed as psoriasis or eczema.

Method of 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 to 15) and these can easily be missed on skin scraping.

Incubation period

It may take two to six 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 one to four 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 to 14 days.

Public health significance & occurrence

Scabies occurs worldwide regardless of age, sex, race, socio-economic status or standards of personal hygiene.

Cyclical epidemics occur at intervals of 10 to 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.

Reservoir

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

Scabies is transmitted by:

skin contact with an infected person
contact with towels, bedclothes and under-garments if these have been contaminated by infested persons within the last four to five days.

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

Period of communicability

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

Susceptibility & resistance

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

Control measures

Preventive measures
Educate the public about the mode of spread, 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% emulsion applied topically, including face and hair (avoid eyes and mucous membranes) and left for 24 hours.

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

For crusted (Norwegian) scabies, the addition of oral ivermectin may also be considered. Seek specialist infectious disease or dermatological advice.

For moderate and severe infections, repeat scabicide treatment in 14 days.

Infested persons should be excluded from school or 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. In order to prevent nosocomial infection, affected staff should be excluded until appropriate treatment has commenced.

Control of contacts
Investigate contacts and source of infestation.

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

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

Outbreak measures

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 reinfestation. Generally, prolonged close contact is required for transmission.

Nursing homes, aged care and other residential facilities

See below, Guide to scabies management in residential care facilities.

Additional sources of information

Centres for Disease Control and Prevention, Scabies fact sheet
Centres for Disease Control and Prevention 1988, ‘Epidemiologic notes and reports scabies in health-care facilities – Iowa’, MMR Weekly, vol. 37, no. 11, pp. 178–9.
Degelau J 1992, ‘Scabies in long-term care facilities’, Infection Control and Hospital Epidemiology, vol. 13, no. 7. pp 421–425.

Infectious diseasesepidemiology and surveillance