Scabies

Abstract

Introduction

Scabies is a common public health problem. In many resource-poor settings, scabies is an endemic problem; whereas in industrialised countries, it is most common in institutionalised communities.

Methods and outcomes

We conducted a systematic review and aimed to answer the following clinical questions: What are the effects of topical treatments for scabies? What are the effects of systemic treatments for scabies? We searched: Medline, Embase, The Cochrane Library, and other important databases up to July 2013 (Clinical Evidence reviews are updated periodically; please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA).

Results

We found five studies that met our inclusion criteria. We performed a GRADE evaluation of the quality of evidence for interventions.

Conclusions

In this systematic review, we present information relating to the effectiveness and safety of the following interventions: benzyl benzoate (topical), crotamiton (topical), ivermectin (oral), malathion (topical), permethrin (topical), and sulfur compounds (topical).

Key Points

Scabies is an infestation of the skin by the mite Sarcoptes scabiei. In adults, the most common sites of infestation are the fingers and the wrists, although infection may manifest in older people as a diffuse truncal eruption.

• It is a very common public health problem. In many resource-poor settings, scabies is an endemic problem; whereas in industrialised countries, it is most common in institutionalised communities.

Topical permethrin seems highly effective at increasing clinical cure of scabies within 28 days.

• Topical permethrin use has been associated with isolated reports of serious adverse effects, including death.

Topical crotamiton seems effective at increasing clinical cure of scabies at 28 days, although it is less effective than topical permethrin.

We found insufficient evidence to judge the effectiveness of topical benzyl benzoate, topical malathion, or topical sulfur compounds for treating scabies.

Oral ivermectin seems more effective at increasing clinical cure of scabies compared with placebo. It may be more effective at increasing clinical cure compared with topical benzyl benzoate. However, it may be less effective than topical permethrin in the short-term.

• There have been isolated reports of severe adverse effects with oral ivermectin, including death and convulsion, but these are rare.

• Observational data suggest that oral ivermectin may be effective in certain circumstances, such as when included in the treatment of hyperkeratotic crusted scabies, in people with concomitant HIV, and in treating outbreaks in residential facilities.

• Although tested in RCTs, oral ivermectin is not presently licensed for the treatment of scabies in most countries. It is only available on a named patient basis in the UK.

Topical lindane use has either been restricted or is not available in many parts of the world owing to the mounting evidence for serious adverse effects. We have not included it in this review. However, it may be the most effective treatment that is locally available in some countries. Harms must be carefully weighed against benefits before it is used.

About this condition

Definition

Scabies is an infestation of the skin by the mite Sarcoptes scabiei. Typical sites of infestation are skin folds and flexor surfaces. In adults, the most common sites are between the fingers and on the wrists, although infection may manifest in older people as a diffuse truncal eruption. In infants and children, the face, scalp, palms, and soles are also often affected. Infection with the scabies mite causes discomfort and intense itching, particularly at night, with irritating papular or vesicular eruptions. The discomfort and itching can be especially debilitating in immunocompromised people, such as those with HIV/AIDS.

Incidence/ Prevalence

Scabies is a common public health problem. In many resource-poor settings, scabies is an endemic problem; whereas in industrialised countries, it is most common in institutionalised communities. Case studies suggest that epidemic cycles occur every 7 to 15 years, and that these partly reflect the population's immune status.

Aetiology/ Risk factors

Scabies is particularly common where there is social disruption, overcrowding with close body contact, and limited access to water. Young children, immobilised older people, people with HIV/AIDS, and other medically and immunologically compromised people are predisposed to infestation and have particularly high mite counts. Although not based on RCT evidence, treating family members and other close contacts at the same time as treating the index case is advisable to minimise reinfection and further spread. Clothing and bed linen belonging to the index case should also be washed.

Prognosis

Scabies is not life-threatening but the severe, persistent itch and secondary infections may be debilitating. Occasionally, crusted scabies develops. This form of the disease is resistant to routine treatment and can be a source of continued reinfestation and of spread to others.

Aims of intervention

To eliminate the scabies mites and ova from the skin; to cure pruritus (itching); to prevent reinfestation; to prevent spread to other people; with minimal adverse effects.

Outcomes

Treatment failure new lesions (i.e., visible burrows and papular/vesicular eruptions) and/or recovery of live mites at 7 or more days after treatment, which is the time it takes for lesions to heal and for eggs and mites to reach maturity if treatment fails; serious adverse effects (e.g., adverse effects requiring hospitalisation).

Methods

Clinical Evidence search and appraisal July 2013. The following databases were used to identify studies for this systematic review: Medline 1966 to July 2013, Embase 1980 to July 2013, and The Cochrane Database of Systematic Reviews 2013, issue 2 (1966 to date of issue). Additional searches were carried out in the Database of Abstracts of Reviews of Effects (DARE) and the Health Technology Assessment (HTA) database. We also searched for retractions of studies included in the review. An information specialist identified the titles and abstracts in an initial search, which an evidence scanner then assessed against predefined criteria. An evidence analyst then assessed full texts for potentially relevant studies against predefined criteria. An expert contributor was consulted on studies selected for inclusion. An evidence analyst then extracted all data relevant to the review. Study design criteria for inclusion in this review were: published RCTs and systematic reviews of RCTs in the English language, at least single-blinded, and containing more than 20 individuals, of whom more than 80% were followed up. There was no minimum length of follow-up. We excluded all studies described as 'open', 'open label', or not blinded unless blinding was impossible. We included RCTs and systematic reviews of RCTs where harms of an included intervention were assessed, applying the same study design criteria for inclusion as we did for benefits. In addition, we use a regular surveillance protocol to capture harms alerts from organisations such as the FDA and the MHRA, which are added to the reviews as required. To aid readability of the numerical data in our reviews, we round many percentages to the nearest whole number. Readers should be aware of this when relating percentages to summary statistics such as relative risks (RRs) and odds ratios (ORs). We have performed a GRADE evaluation of the quality of evidence for interventions included in this review (see table). The categorisation of the quality of the evidence (high, moderate, low, or very low) reflects the quality of evidence available for our chosen outcomes in our defined populations of interest. These categorisations are not necessarily a reflection of the overall methodological quality of any individual study, because the Clinical Evidence population and outcome of choice may represent only a small subset of the total outcomes reported, and population included, in any individual trial. For further details of how we perform the GRADE evaluation and the scoring system we use, please see our website (www.clinicalevidence.com).

Table.

GRADE Evaluation of interventions for Scabies.

Important outcomes	Treatment failure
Studies (Participants)	Outcome	Comparison	Type of evidence	Quality	Consistency	Directness	Effect size	GRADE	Comment
What are the effects of topical treatments for scabies?
2 (194)	Treatment failure	Topical permethrin versus topical crotamiton	4	–2	0	0	+1	Moderate	Quality points deducted for sparse data, unclear allocation concealment, and unclear blinding; effect-size point added for RR <0.5
3 (457)	Treatment failure	Topical permethrin versus oral ivermectin	4	–1	–1	0	0	Low	Quality point deducted for incomplete reporting of results; consistency point deducted for inconsistent results among studies (at 2 weeks)
1 (158)	Treatment failure	Topical benzyl benzoate versus topical sulfur ointment	4	–2	0	0	0	Low	Quality points deducted for sparse data and short follow-up
What are the effects of systemic treatments for scabies?
1 (55)	Treatment failure	Oral ivermectin versus placebo	4	–2	0	0	+1	Moderate	Quality points deducted for sparse data and short follow-up; effect-size point added for RR <0.5
2 (102)	Treatment failure	Oral ivermectin versus topical benzyl benzoate	4	–1	-1	0	0	Low	Quality point deducted for sparse data; consistency point deducted for inconsistent results among studies

We initially allocate 4 points to evidence from RCTs, and 2 points to evidence from observational studies. To attain the final GRADE score for a given comparison, points are deducted or added from this initial score based on preset criteria relating to the categories of quality, directness, consistency, and effect size. Quality: based on issues affecting methodological rigour (e.g., incomplete reporting of results, quasi-randomisation, sparse data [<200 people in the analysis]). Consistency: based on similarity of results across studies. Directness: based on generalisability of population or outcomes. Effect size: based on magnitude of effect as measured by statistics such as relative risk, odds ratio, or hazard ratio.

Glossary

High-quality evidence

Further research is very unlikely to change our confidence in the estimate of effect.

Low-quality evidence

Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.

Moderate-quality evidence

Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate.

Onchocerciasis

A tropical disease caused by the filarial worm Onchocerca volvulus. The disease affects the skin, causing disfiguration and itching, and is a major cause of blindness, particularly in West Africa. The worm is transmitted to humans in its larval stage through the bite of the black fly, genus Simulium.

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