11/14/24, 10\:44 AM Scabies

Scabies

Table of contents
Key points ⚡
Succinct notes to superpower your revision
Scabies\: highly contagious skin infestation caused by the mite S a r c o p t e s s c a b i e i var. h o m i n i s , spread by close contact.
Prevalence\: a
facilities.
Risk factors\: direct skin-to-skin contact, fomites (bedding, clothes), poverty, overcrowding, warm/humid environments,
immunosuppression (HIV, immunosuppressive medication).
Symptoms\: severe pruritus worse at night, sleep disturbance, may be asymptomatic for up to 6 weeks in
Rash appearance\: erythematous papules or vesicles, surrounding dermatitis, characteristic burrows (~1cm irregular tracks),
typically found in webbing of
Crusted scabies\: severe form with thousands/millions of mites, very contagious, causes crusted, scaly rash, often less
itchy.
Diagnosis\: clinical, con
Management\:
General advice\: wash all bed linen, clothes, toys; treat close contacts concurrently.
Topical therapies\: permethrin 5% cream (
benzoate 25% emulsion (second-line).
Systemic therapies\: ivermectin (e
Complications\: secondary bacterial infection (commonly S t r e p t o c o c c u s p y o g e n e s or S t a p h y l o c o c c u s a u r e u s ), appropriate antibiotics to prevent sequelae (glomerulonephritis, rheumatic fever).
treated with
Article 🔍
A comprehensive topic overview

Introduction

Scabies is a highly contagious skin infestation caused by a mite. It is spread by close contact and is more common among
disadvantaged populations. It is readily treatable, and a broad approach to treatment is important to ensure eradication.
Estimates of prevalence are highly variable, but scabies is thought to a
the elderly, and people residing in long-term care facilities are at the highest risk.
Prevalence can vary among ethnic groups depending on exposure to risk factors. Scabies is more prevalent in indigenous
and refugee communities, due to socioeconomic disadvantage and overcrowding. It is considered a neglected tropical
disease.
2

Aetiology

Scabies is caused by a parasitic mite, S a r c o p t e s s c a b i e i var. h o m i n i s . It is transmitted through direct skin-to-skin contact,
or less commonly indirectly via fomites.
1
The clinical features of scabies infection primarily result from a local allergic reaction to the presence of the scabies mite,
rather than being directly caused by the mite itself.
https\://app.geekymedics.com/notebook/2609/ 1/511/14/24, 10\:44 AM Scabies

Risk factors

Key risk factors for contracting and transmitting scabies include\:
Direct contact\: skin-to-skin contact with a person with scabies, which can be quite brief (such as through holding hands
or sexual contact).
Fomites\: indirect contact through bedding, clothes, or towels, although this is far less common than direct contact.
Living conditions\: poverty and overcrowding are key risk factors. This includes institutional care facilities, such as
residential aged care homes, hospitals, and prisons.
Environment\: transmission is more common in warm, tropical, humid environments.
Immunosuppression\: HIV infection or immunosuppressive medication increases the risk of infection with scabies and
may also lead to more severe and persistent infection.
3

Clinical features

The clinical features of scabies infection primarily result from a local allergic reaction to the presence of the scabies mite,
rather than being directly caused by the mite itself.

History

In the
shorten signi
severe enough to cause sleep disturbance.
4
On further history taking, patients may have other family members or close contacts with similar symptoms. It is important
to take a detailed social history for potential risk factors (such as poor living conditions and overcrowding), to determine
potential contacts and if additional holistic support may be required.

Clinical examination

Scabies is typically found in the webbing and sides of
is due to a local hypersensitivity reaction to the mite.
The appearance of the rash is quite variable but can include erythematous papules or vesicles, and surrounding
dermatitis.
Burrows are characteristic and appear as small irregular tracks ~1cm in length, classically found in the webbed spaces
between the
https\://app.geekymedics.com/notebook/2609/ 2/511/14/24, 10\:44 AM Scabies
Figure 1.Scabies a
5

Clinical presentations

Crusted scabies (sometimes called Norwegian scabies) is a severe variant of scabies where an individual is infected with
thousands or millions of mites (compared with 5-20 in a typical infection). It is very contagious and causes a crusted, scaly,
keratotic rash, often in the
6
Figure 2.Severe crusted scabies.
7
Representative images in diverse skin types
Because of image reproduction rules, we are only able to directly include images with creative commons licencing.
Unfortunately, the majority of images of dermatological conditions available under this licence are in Caucasian
patients and fair skin tones.
We have included representative images here that we are not able to reproduce in this article directly, which we
encourage you to review\:
Scabies on the hands and feet of children with pigmented skin (ethnicity not speci

Di

Because the scabies rash can be quite variable in appearance, di
skin infections, urticaria and more. It is important to always consider scabies when evaluating itchy rashes.

Investigations

Scabies can be diagnosed clinically, but investigations can assist with the diagnosis.
Dermatoscopy is a useful adjunct to clinical examination, to assist with visualising burrows that may be too small to see
macroscopically.
Skin scraping and biopsy can be useful for histopathology, but it is important to sample the burrow itself, rather than the
surrounding rash.
https\://app.geekymedics.com/notebook/2609/ 3/511/14/24, 10\:44 AM Scabies

Management

General advice

Scabies can be di
Good hygiene is important. Washing all bed linen, clothes, toys, and other items is recommended to eradicate scabies from
the household. Close contacts of a person with scabies will need to be examined and treated concurrently.

Topical therapies

Permethrin 5% cream is the treatment of choice for scabies, applied to the entire body (excluding the face) and left on for 8
hours, with treatment repeated in 7 days. Some guidelines do not recommend permethrin for use in children younger than
2 months of age, so it is important to check local guidelines.
Benzyl benzoate 25% emulsion is used as a second-line treatment in cases of allergy or treatment failure but can cause
skin irritation.
8

Systemic therapies

Ivermectin is an e
It is usually given at a dose of 200µg/kg.
Ivermectin is e
contain widespread outbreaks (e.g. in care facilities).

Complications

Secondary bacterial infection of scabies rashes is common, due to patients scratching the highly pruritic rash, most
commonly with S t r e p t o c o c c u s p y o g e n e s (a group A streptococcus) or S t a p h y l o c o c c a l a u r e u s .
It is important to recognise and treat secondary infections early with appropriate antibiotics, because of the risk of
sequelae from group A streptococcus including glomerulonephritis and rheumatic fever.
Due to the underlying social determinants of health, many patients who are at highest risk of scabies are also at risk of
these signi
3

References

DermNet NZ. S c a b i e s . 2015. Available from\: [LINK]
WHO. S c a b i e s a n d o t h e r e c t o p a r a s i t e s . 2020. Available from\: [LINK]
Australian Family Physician. S c a b i e s . 2017. Available from\: [LINK]
British Association of Dermatologists. H a n d b o o k f o r M e d i c a l S t u d e n t s a n d J u n i o r D o c t o r s . 2020. Available from\: [LINK]
Wikimedia Commons. S c a b i e s a CC BY-SA]. Available from\:
[LINK]
DermNet NZ. S c a b i e s . 2015. Available from\: [LINK]
DermNet NZ. S e v e r e c r u s t e d s c a b i e s . Licence\: [CC NC BY-SA]. Available from\: [LINK]
eTG Complete. S c a b i e s . 2020. Available from\: [LINK]

Reviewer

Consultant Dermatologist
https\://app.geekymedics.com/notebook/2609/ 4/511/14/24, 10\:44 AM Scabies

Related notes

Acne vulgaris
Basal Cell Carcinoma (BCC)
Cellulitis
Cutaneous Squamous Cell Carcinoma (SCC)
Erythema Multiforme

Test yourself

Contents

Introduction
Aetiology
Risk factors
Clinical features
Di
Investigations
Source\: geekymedics.com
https\://app.geekymedics.com/notebook/2609/ 5/5