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Scabies

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VOL: 97, ISSUE: 22, PAGE NO: 57

Margaret Jenkins, RGN, SCM, is a community infection control sister, Scarborough and North East Yorkshire Healthcare NHS Trust

Scabies (Sarcoptes scabiei) or human itch mite is one of the most common causes of itching dermatoses in the world (Maguire and Spielman, 1994). The prevalence of the disease is cyclical, with peak prevalence occurring every 15-20 years, lasting for approximately two to three years. This fluctuation in incidence in the developed world is thought in part to be due to professional intervention (Meinking et al, 1995).

The mite

The female mite, twice the size of the male, is approximately 0.4mm in length and has four pairs of legs. The mites are situated in the deeper parts of the epidermis and are surrounded by the prickle cell layer, on which they feed and burrow. Burrows are lined by scar tissue which prevent them from collapsing. Mites possess an exceedingly thin membranous skin through which gaseous exchange occurs and this enables them to do away with a complex breathing apparatus. Because it is used, in effect, as a lung, the skin of scabies mites is also permeable to water vapour. Due to this, they are unable to leave the burrows in which they live, as to do so would result in death from dehydration.

Mites produce numerous faecal pellets which they are forced to retain in their tunnels. These pellets, from which an allergen seeps, are glued to the floor of the tunnel along with the large eggs laid by the females. The allergen from within the faeces then diffuses from the burrow into the blood stream, producing an allergic response that causes the characteristic itch associated with scabies. Up until this time, which is approximately four to six weeks, the host is unaware of the hive of industry going on in the epidermis.

Once the itching begins, burrows become excoriated, due to scratching, and mites and eggs are destroyed. In this way their numbers are reduced, leaving most sufferers with an average number of no more than a dozen mites.

Clinical features

Although the major symptoms are dermal, it should be remembered that they are produced by systemic involvement, and presentation depends on the immune status of the patient. Due to this, symptoms and clinical features fall into three categories: classical, crusted and atypical scabies.

Classical scabies

This form is found in healthy people with a normal immune system. The major symptom is an initial inconspicuous rash which is very itchy, particularly at night, and it is not unusual for patients to scratch themselves until they bleed. The distribution of the rash is characteristic, being found on the wrist, finger webs, forearms, axillary folds, side of the chest, around the waist, the lower quadrants of the buttocks and the inside of the legs and ankles. The genitals can also be affected and soles of the feet in children. Only in infancy does this condition affect the face. The rash may not appear in all these areas at once, but is always bilaterally symmetrical, affecting both sides of the body alike.

Crusted scabies

This type is sometimes referred to as Norwegian scabies and is known to be frequently misdiagnosed (Almond et al, 2000; Gach and Heagerty, 2000). Crusted scabies occurs in immuno-compromised patients and has been well documented as being problematic in those with AIDS (Portu et al, 1996).

Due to poor immune response, the itchy rash does not occur, and so in the early stages there is little sign of anything wrong. However, the number of mites may be enormous, with thousands being present anywhere on the body, including the head. The skin eventually becomes thick, crusted and unsightly. This form of the infection is highly contagious and is often the source of outbreaks in residential care and schools (Xavier, 1998; Marshall et al, 1995).

Atypical scabies

This occurs in individuals whose immune system is immature or impaired and often affects very young and elderly people. More mites are produced than in classical scabies, particularly on the hands, and consequently this type of patient is extremely contagious. Symptoms are subclinical, making diagnosis very difficult. However, the rash still tends to be bilaterally symmetrical and avoids the head and centre of the back and chest.

Transmission

Prolonged skin-to-skin contact is required and thus the condition is more commonly spread among families, sexual partners, hospitals and nursing homes. Experiments carried out in the 1940s demonstrated that the scabies mite is not readily transmitted via inanimate objects such as bed linen and clothing (Andrews, 1978).

Diagnosis

The distribution of the rash and a history of intense itching, particularly at night, is usually indicative of classical scabies, making this type the easiest to diagnose. Checking for the presence of symptoms in family members, colleagues and patients often provides a clue.

Identification of a burrow with the mite at one end is diagnostic. This usually requires the assistance of a hand lens magnified eight or 10 times and a good light, as magnification dims the image.

The assistance of a dermatologist, an experienced GP or an infection control/public health nurse is often required to diagnose this condition, most particularly in the case of atypical and crusted scabies.

Treatment

Treatment involves application of a scabicide to the complete skin surface, including the scalp, whether hair-bearing or not.

Two treatments are required for patients and contacts with symptoms, the second application being applied three to seven days later, as unhatched eggs are not killed by the initial treatment. Only one application of a scabicide is needed for asymptomatic contacts. Everyone identified for treatment should be treated simultaneously or within the same 24-hour period.

Even with fastidious treatment, the cure rate is not 100%. Most apparent failures are due to either inadequate application of the insecticide or failure to identify a contact. The amount of scabicide prescribed should correspond with the size and weight of the patient, or treatment will be compromised.

The success rate will be greatly enhanced by good communication and instructions regarding application of the treatment. Written directions should be provided (Fig 1).

Available treatments are permethrin and malathion benzyl benzoate for adults. For crusted scabies several treatments on consecutive days are required, as crusts impede penetration of the medication.

Management of single cases and individual families is usually fairly straightforward. However, the diagnosis even of a single case in an acute hospital or residential home is fraught with potential problems.

The acute setting

Outbreaks in acute wards are rare and usually only single cases are seen. However, before deciding on management, an assessment needs to be undertaken of the following factors:

- The patient’s length of stay;

- Diagnosis;

- Physical and mental health;

- Dependency;

- Extent of contact with other patients;

- Possibility of transfer from another ward;

- Type of scabies;

- Contacts - family and close friends;

- Symptomatic contacts.

Good communication and support is vital, particularly in relation to such basic information as transmission, incubation period and infection control procedures. The use of a policy relating to this condition is essential.

Universal precautions are all that is required, with the recommendation that gloves be worn for lengthy procedures involving contact with the skin. No special precautions are required for bedlinen or clothing. However, some dermatologists recommend washing bedlinen the morning after completion of treatment, although this does not correlate with research (Andrews, 1978).

Isolation of the patient is not necessary, except in the case of crusted scabies. This could be potentially harmful psychologically, as scabies has always been associated with a degree of stigma.

Once infection control precautions have been implemented, arrangements should be made to treat the patient and any close contacts.

Long-term care

The diagnosis, treatment and management of scabies in nursing and residential care can be extremely difficult, stressful and labour-intensive. Controlling the infection depends on good communication, education and teamwork. The extent of treatment should be based on risk assessment which includes the number of confirmed and symptomatic cases. Management varies but a suggested approach is provided in Fig 2.

In the early stages, discussion needs to take place between representatives of all interested parties, including public health and/or infection control and a dermatologist. Large outbreaks may necessitate an outbreak control meeting. The management and treatment protocol should be explained to all concerned, with copies provided for staff, relatives and, where appropriate, patients.

Prescriptions need to be obtained from GPs and a copy of the protocol supplied. Ideally, everyone should be treated with the same insecticide. Failure to do so causes confusion, extra work and jeopardises the success of the exercise. The treatment day should be planned well in advance and extra staff deployed.

For several weeks afterwards, the home needs to be monitored for early signs of renewed problems. However, it is important to stress that itching remains a common symptom for several weeks after treatment.

Prevention

Education of staff, particularly in relation to early reporting of symptoms, is vital. Other requirements are as follows:

- Universal precautions;

- Early diagnosis;

- Adequate contact tracing;

- Correct application of treatment;

- Post-outbreak monitoring;

- Policy production;

- Ongoing education.

Conclusion

Keeping Sarcoptes scabiei at bay will require all health care staff to be vigilant in order to facilitate early intervention and treatment.

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