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Scabies: hugely irritating and highly contagious

Gill Bedson
RGN DPSN NPDip BScHealthStudies
Lead Nurse
Luton Walk-in Centre
Luton Bedfordshire
E:gill.bedson@luton-pct.nhs.uk

Scabies is caused by infestation by the parasite Sarcoptes scabiei, which is a skin mite that is about 0.35mm long (see Figure 1). The female mite tunnels into the stratum corneum and deposits eggs along the burrow. The larvae hatch after a few days and create new burrows, where they remain until maturity. The main symptoms of scabies are caused by a hypersensitivity reaction to the mites and to their saliva and faeces.(3)

[[NIP13_fig1_25]]

Symptoms
The symptoms usually occur 2-6 weeks after infestation. Itching is the most common presenting symptom and is usually most intense when the person is in bed. This coincides with the appearance of a rash.
The rash is symmetrical and is usually made up of red papules (see Figure 2), although vesicles or nodular reactions can on occasion be seen.

[[NIP13_fig2_25]]

The rash is most prevalent on the inside of the thigh, the axillae, buttocks and umbilical region.

Predisposing factors

  • Scabies is transmitted by close physical contact and is more common in areas of overcrowding or where individuals are in close proximity to each other, such as schools or nursing homes.
  • In infants, young children or ­immunocompromised patients there is more ­likelihood of severe infection with infestation above the neck.
  • Norwegian scabies is more contagious and results in more severe infection. This often imitates eczema or psoriasis and can result in delayed treatment and increased opportunity to spread. This form of ­scabies is less common and tends to affect the ­immunocompromised and elderly ­population.(4)

Diagnosis
A full history and physical examination of the skin are required. It is important to examine the whole body to help with differential diagnosis. Scabies can be confused with a number of other diagnoses, including pubic lice or body lice, insect bites or other dermatological conditions, including atopic eczema, contact dermatitis, lichen planus, dermatitis herpetiformis or papular urticaria.(5)

[[NIP13_fig3_26]]

If a family member is displaying the same symptoms this increases the likelihood of scabies.
The diagnosis is confirmed by the examination of skin scrapings taken from the burrows, revealing mites, eggs or faeces. Burrows can sometimes be difficult to find; they are most common in the finger webs and at the wrist and elbow. They can also be found on the ankles, feet, nipples and genitals. However, in the elderly patient the distribution can be more general.
A scabies burrow appears as a greyish, scaly lesion about 0.5cm in length. It looks like a twisting line on the surface of the skin, which fades at one end and has a small vesicle at the other. The burrow ink test (BIT) can help with identification.(6) This entails applying a felt-tip pen over the suspected area, removing the ink with alcohol and then examining the area for burrows that will be highlighted with the remaining ink.

Complications
The most obvious complication is infestation of a contact. Secondary infection can occur from scratching, and eczematous eruptions can also be a complication.

Treatment
Scabies will persist indefinitely unless treated. All members of the family and sexual contacts should be treated simultaneously (even if they are asymptomatic) as scabies is highly contagious, and there is a latent period before symptoms develop.
People should ideally receive written advice on the correct application of treatment, the importance of treating the whole household and sexual contacts simultaneously, and the possibility that residual itching may persist for several weeks after treatment. The residual itch can be treated with antihistamines.(7)
Outbreaks of scabies in a residential or nursing home should be referred to the local consultant in communicable disease control, so that all residents, staff and their families can be treated simultaneously on an agreed treatment date.(8)
Permethrin dermal cream is the preferred treatment option, and malathion is the secondline treatment option.(9)

Application of treatment
Two applications of treatment should be used, a week apart.
Apply treatment to the whole body from the neck down, especially between the fingers and toes and under the nails.
Thorough application to cool, clean, dry skin is important to prevent treatment failure. Preparations should not be applied after a hot bath because this increases systemic absorption and removes the drug from the treatment site.
Additional treatment of the scalp, neck, face and ears is recommended in elderly people, young children and immunocompromised people and in treatment failure. Mites are more likely to be found at these sites in these individuals.
For children under two years, a single application is usually effective. If the hands are washed, the liquid or cream must be reapplied.
Scabies is not usually transmitted via clothes, towels or bed linen. Washing these articles is not required to prevent reinfestation and transmission to others, unless the person has crusted (Norwegian) scabies.

Treatment of itch
Use of a sedative antihistamine at night may be of value to prevent the intensity of itch when at its worse.
Crotamiton cream/lotion may have a place, although there is no evidence of its antipruritic qualities.(10)

Practice ­pointers

  • History and ­physical ­examination are important in ­distinguishing this infestation from other causes.
  • The burrow ink test can help in diagnosis.
  • The most common ­presenting complaint is ­itching, which is often worse at night.
  • Nurse prescribers can prescribe for this irritating ­problem.
  • Treatment failure is usually due to poor application of skin creams.
  • It is important to treat patient contacts as scabies is highly contagious.

Case study
A 21-year-old woman presented complaining that she was still experiencing symptoms of scabies 6 weeks after treatment of the condition. The rash had started to get worse again, and she was having difficultysleeping due to the increased irritation.
On further questioning it became apparent that she had not understood the instructions that a second application of treatment was required, 7 days after the first, and had therefore only used one application. Examination revealed new evidence of burrows and rash. After discussion it was decided to retreat with permethrin dermal cream and time was spent reviewing how treatment should be applied. Written information concerning this process was given to ensure concordance. Her partner was treated simultaneously.

References

  1. Barrett NJ, Morse DL. The ­resurgence of scabies. CDR Review 1993;3:R32-4.
  2. Downs AMR, Harvey I, Kennedy CTC. The epidemiology of head lice and scabies in the UK. Epidemiol Infect 1999;122:471-7.
  3. Figueroa J. Scabies. In: Figueroa J, Hall S, Ibarra J, editors. Primary health care guide to common UK parasitic diseases. London: Community Hygiene Concern; 1998. p.25-35.
  4. Roberts DT, editor. Lice and scabies: a health professional's guide to ­epidemiology and treatment. London: Public Health Laboratory Service; 2000.
  5. Hunter DJ, Savin RC, Dahl MV. Infestations: scabies. In: Hunter JAA, editor. Clinical dermatology. 2nd ed. Oxford: Blackwell Science; 1995.p.197-201.
  6. Sharbaugh RJ. Scabies: an itchy problem. Home Care Provider 1997;2(3):115-16.
  7. Shuster S. Antihistamines in the treatment of urticarial disorders. Cutis 1988;42:26-8.
  8. Clinical Effectiveness Group. National guideline for the management of scabies. London: Clinical Effectiveness Group (Association for Genitourinary Medicine and the Medical Society for the Study of Venereal Diseases); 1999.
  9. Walker G, Johnstone P. Skin ­disorders: scabies. Clin Evid 2000;3:839-45.
  10. BNF 41. British National Formulary. 41st ed. London: British Medical Association and the Royal Pharmaceutical Society of Great Britain; 2001.

Resources
Department of Dermatology
University of Iowa Provides many dermatology images
W:http://tray.dermatology.uiowa.edu/Home.html