SCABIES - NOTES

 INTRODUCTION-

 Scabies is caused by the mite, Sarcoptes scabiei var. hominis, which burrows into the upper layer of the skin - the stratum corneum. The female lays eggs in the tracks of the burrows. The eggs and mite proteins produce an allergic reaction and this reaction, is responsible for the characteristic itching and rash. Scabies is normally acquired from skin-to-skin contact with another individual who has scabies. It is frequently acquired among children and can also be sexually transmitted.  It is sometimes transmitted from care providers or beddings. The incubation period for those without previous exposure to scabies is 2 to 6 weeks. Individuals who have been previously infested with scabies develop symptoms within 1 to 5 days of re-exposure. 

CLINICAL MANIFESTATION-

 Classical Symptoms

 • The main symptom is itch, which usually develops within 2 to 6 weeks after infestation.

 • The itch is generalized, very intense and intractable. 

• The itch is worst at night.

 • History of itch among family members within the same period Physical Examination

 • Presence of small erythematous papulovesicular lesions predominantly over anterior axillary folds, nipple area, periumbilical skin, elbows, volar surface of the wrists, interdigital web spaces, belt line, thighs, buttocks, penis, scrotum, ankles and typically except for the head, face, and neck in adults.

 • Infants and young children may develop similar lesions diffusely, but unlike adults, lesions are common on the face, scalp, neck, palms and soles.

 2 • Scabies burrows are most easily found on the hands, especially finger webs and on the wrists; other sites of predilection are the feet, axillae, umbilicus, male genitalia and breast areolas in women. 

• In infants, burrows are common on the palms and soles, and sides of the feet. They can also be found on the heads of infants particularly post auricular folds.

 • The typical burrow is a serpiginous tract that measures 1cm in length. It may be obscured by excoriation marks or by vesiculation in infants.

 • The reddish-brown nodules of scabies are seen in axillary and inguinal regions, wrists and male genitalia and these may persist for several months. These nodules are caused by delayed hypersensitivity reaction to the female mite, its eggs and faeces (scybala) deposited in the epidermis, rather than by an active infection.

 • Some of the lesions may be altered by excoriations, eczematisation and secondary bacterial infection.

Crusted (Norwegian)-

 • It is an uncommon form of scabies  

• It is highly contagious with huge numbers of mites 

• More common in immunocompromised and neurologically impaired individuals, but may also occur in otherwise healthy subjects.

 • Pruritus may be minimal or absent, or the host may be physically incapable of scratching.

 • Characterized by diffuse hyperkeratosis, associated with variable degree of underlying erythroderma.

 • Hyperkeratosis and crusting are particularly severe on the hands, including the palms and soles, under the fingernails, on the ears, trunk and extremities.

DIAGNOSIS-

 • It is important to establish a firm diagnosis of scabies before treatment. Antiscabetic therapy may aggravate other dermatoses such as atopic dermatitis and cause unnecessary skin irritation.

 • Scabies should be suspected in infants or children with generalized pruritus of recent onset and the characteristic eruptions.

 • Other family members are usually, but not invariably affected. A history of scabies in a family member or contact with scabies should be sought out specifically.

 • Scabies diagnosis is confirmed by microscopic identification of the mite, eggs or scybala.

 Dermatoscopy and digital photography are non-invasive and effective methods for identifying the presence of scabies mites.

TREATMENT - 

General measures

 • Patients must receive detailed information about scabies infestation and therapeutic options, including the amount of drug to be used and proper administration.

 • Topical treatment must be applied to the entire skin surface, from jawline downwards including all body folds, groin, navel and external genitalia, as well as the skin under the nails (especially crusted scabies).

 • In adults with classical scabies, treating the face is controversial, but in babies, the face must be treated, because transmission may occur from breastfeeding. At any time during treatment, medications should be re-applied if it is washed off i.e. after hand washing. 

• If the treatment is applied by someone without scabies, this person should wear medical gloves during application.

 • Patients with scabies and their close physical contacts, even without symptoms, should receive treatment at the same time. Prescriptions must be provided for all household members and sexual partners. 

 • After completion of treatment, patients should use fresh, clean bedding and clothing. If possible, potentially contaminated clothes and bedding should be washed at high temperature (>50°C) or kept in a plastic bag for up to 72 hours, because mites that are separated from the human host will die within this time period.

 • The use of insecticidal powder or aerosol products should be reserved for materials or objects that cannot be washed.

Treatment of infection in scabies-

 Secondary bacterial infection is a common complication in scabies due to disruption of the epidermal barrier caused by excoriations.

 • Treat with systemic antibiotics which covers gram positive organism – for a minimum of 7 days 

• The timing of antibiotic commencement depends on the condition of the patient; it can be started concurrently with scabicides or delayed for 48 hours to allow partial healing of the erosions.

 • Use antiseptic soaks/bath e.g. KMnO4 (1:10,000) in impetiginized scabies

 • Topical antibiotic is not indicated in patients who are already treated with systemic antibiotics 

Treatment of Nodular Scabies-

 • Individual nodules can be treated with: o Topical anti-inflammatory agents; e.g. topical corticosteroids of mid potent to potent for a short duration of 2 weeks.  Crotamiton cream twice daily for 7 to 14 days.

Treatment of itch in scabies-

 Itching usually persists for about one to two weeks after successful treatment but it should be evaluated if prolonged. Causes of persistent itching include cutaneous irritation, allergic contact dermatitis to medicaments, post-scabetic eczema or possible treatment failure (please refer below). 

The treatment includes: 

 i. Antihistamines: chlorpheniramine, hydroxyzine, diphenhydramine, dexachlorpheniramine. Sedative antihistamines must be used with caution in children less than 2 years old.

 ii. Corticosteroids: topical or short course of oral steroids (0.5mg/kg depending on the severity).

 iii. Emollients: regular application of emollients for dry and eczematous skin.

Treatment of contacts 

A contact is defined as someone who has had prolonged (greater than 10 minutes on any one occasion) skin to skin contact over the previous two months. Members of the affected household and all close contacts should be treated, even in the absence of symptoms, at the same time. All contacts need to be managed in exactly the same way as the patient; however for most, only one treatment is needed. Only symptomatic contacts require two treatments (with permethrin 5%).

Treatment for fomites Fomites 

should be treated concurrently, these include:

 • Underwear, clothing, towels, bed linen and personal effects such as slippers, bed jackets and dressing gowns used by the affected person in the 72 hours prior to treatment should be laundered using a hot wash cycle (>50°C) or hot tumble dried to kill the mites.

 • If items are unable to be laundered or hot tumble dried, place them in a plastic bag and leave them for 72 hours before airing and reusing.

 • Mattresses should be thoroughly vacuumed, ironed or steam cleaned, paying particular attention to the seams.

 • Where possible, amenities such as toilets and chairs should not be shared (until 24 hours after the first treatment).

FOLLOW UP

• Repeat visits 2 weeks and 4 weeks after initial treatment are recommended

. • Patients should be reviewed again at the end of one month to ensure that he/she is cured from scabies. This is the length of time taken for lesions to heal and in case where there is inadequate treatment, for residual eggs and mites to reach maturity causing symptoms to reappear. Patients can be re-treated if necessary.

References 

1. Strong M, Johnstone P. Interventions for treating scabies. Cochrane Database of Systematic Reviews 2007, Issue 3. 2. European guideline for the management of scabies G R Scott. International Journal of STD & AIDS 2001; 12 (Suppl. 3): 58 - 61 3. Guideline for the diagnosis and treatment of scabies in Japan (second edition). N. Ishii et al. Journal of Dermatology 2008; 35: 378–393 4. Treatment of scabies: newer perspectives. K Karthikeyan. Postgrad Med J 2005;81:7–11 5. Scabies therapy for the Millennium. Terri L. et al. pediatric dermatology. 2000. Vol 7(2): 154-156