Overview of scabies mite
Scabies is a ubiquitous skin infestation caused by the mite Sarcoptes scabiei. It is a common condition with up to 130 million people infected worldwide. It is thought to affect most countries but those most at risk are the young and elderly/frail in poor communities. The highest prevalence is seen in countries with a hot and humid climate along with significant overcrowding problems.1
In the UK, scabies is most common in densely populated urban areas, in women and children, in the north of the UK and during the winter months.5 Clusters can occur in highly populated environments such as schools, nurseries, hospitals and nursing homes.6
The scabies mite is highly contagious as it is transmitted by prolonged direct skin to skin contact.2,9 It is theoretically possible for transmission to occur from bed linen and clothes but only if used by an infested person immediately prior to contact.3
Infestation is complete when a female mite burrows into the skin and lays eggs. Two to three days later the larvae emerge and dig new burrows. The cycle is repeated over 10 to 19 days.4 A person with scabies usually has about 10-15 mites.9
The mite itself is only just visible to the naked eye with the use of a magnifying glass as the female is slightly less than 0.5 mm in size.
History of itch in the patient, and usually the rest of the family, is almost pathognomonic, although some patients are reluctant to admit to itch and others appear genuinely not to suffer with this.4,9 The pathognomonic sign is the burrow (superficial wavy and scaly line) but other features include papules, vesicles, pustules and nodules.4
The healthcare professional should look for burrows at the sites commonest for the age and sex of the patient. In infants and children these are palms and soles, face, head, neck and scalp.4 In adults it is rare to have face and neck involvement; hands and feet are more common sites. It is also worth considering the breasts in women and genitalia in men.
Very young children can often develop eczematous erythema in reaction to the infestation that can be florid, targeting the trunk.4 It is common for young babies not to scratch so other signs must be sought such as being miserable or off their feeds.4
Patients with the crusted or Norwegian form of scabies can have thousands of mites compared to the normal infestation of around 10-15 mites per patient.7
If crusted scabies is present, clinicians should explore immunodeficiency as an underlying cause.9
Diagnosis is often clinical, relying either on the signs or history of contact with an affected individual.
Microscopy can be taken from the skin in order to aid the diagnosis.9
The females can be removed from the burrows with sterile forceps for laboratory confirmation if required. However, the typical track of the mite in the skin, with darker areas in the track resulting from its faeces is characteristic and often negates the need for laboratory confirmation.
The management of scabies is in three parts:...