Simple notes on skin infestation

1.SCABIES
Clinical Features
Symptom occurs 3 to 4 weeks after the acquire of the infection. This latency period may not occur if an individual has had a previous infestation. Itchiness is the most obvious symptom of scabies. It is worst at night time when the patient is warm.
The pathognomonic sign of scabies is a burrow; it is a short, wavy, dirty-appearing line crossing skin lines. They may occur on the wrists, the borders of the hands, the sides of the fingers and the finger web-spaces, the feet particularly the instep and in male the genitalia and nodules on scrotum. Burrows are uncommon on the trunk in adult but they may be found in elderly and infants. Pruritic papules which accompany hypersensitivity reaction occur around axillae, peri-areolar regions, peri-umbilical regions, buttock and thighs. The lesions do not occur above the neck-line. Secondary change like eczematous change frequently give confusion to the clinical picture. Inappropriate use of topical steroid may change the clinical picture to mimic other dermatoses.
1.4. Diagnosis
Absolute confirmation can only be made by the discovery of the burrows and microscopic examination. A burrow is gently scraped off the skin with a blunt scalpel, and the material placed in a drop of mineral oil on a microscopic slide. Oil mounting of the specimen sharpens the microscopic image and does not kill the mites which may be present (as potassium hydroxide would). Presence of mites, eggs or fragments of egg-shells confirms the diagnosis. Other diagnostic tests include needle extraction of mite, epidermal shave biopsy and punch biopsy.
1.5. Treatment
It is important that all members of the household and all close contacts should be treated simultaneously. Elderly members of the family often resent for treatment but they can be asymptomatic reservoirs of infection.
Treatment must be given on two consecutive nights but not for longer. Anti-scabies preparations are primary irritants which will eventually cause eczema, patients should be warned about over-use. The patient should first take a bath, and this is followed by a brisk toweling to open the hydrated burrows. Hot bath increases the percutaneous absorption of the drug and may cause toxicity. Benzyl benzoate employed as a 25% emulsion should remain on the skin for 24 hours. The emulsion is most conveniently applied with a 2" paint brush applied to the whole body from the neck down including the genitalia and the soles of the feet. This anointing is repeated on the following morning. On the following evening the patient should take a bath again and has the bed-linen and clothing changed which are then laundered in the usual way.
After the scabicidal treatment, pruritus may persist for a further 2 weeks. A topical antipruritic such as crotamiton cream may be applied on residual itchy areas. Postscabetic eczema can be treated with topic steroid.
Secondary infection should be treated with a systemic antibiotic. If eczematisation is severe, a non-irritant scabicide, preferably in an aqueous base, should be used.
Treatment of neonates - 6.25% benzyl benzoate emulsion may be used. Other alternatives include 10% crotamiton cream (applied nightly for 2 nights and washed off after the second application), 10% sulphur in petrolatum (applied nightly for 3 nights and washed off 24 hours after the last application) and 5% permethrin cream.
Other drugs used:
1) 1% gamma benzene hexachloride (Lindane) - a single application wash off after 12-24 hours is usually recommended. It is not recommended to be used in young children, pregnant and nursing women, and those with neurological diseases.
2) malathion - malathion 0.5% in aqueous base has been used as scabicide. It should be left on the skin for 24 hours. The advantage over BBE is that it is much less stinging and acceptable.
3) permethrin - 5% dermal cream employed as a single application, wash off 8-12 hours. It is of low toxicity, and a single application which is removed in 8-10 hours is adequate. The disadvantage is that it is much more expensive than BBE or malathion.
4) monosulfiram - 25% solution diluted with 2-3 parts of water to be applied daily for 2 or 3 days.
5) crotamiton - 10% crotamiton cream is not highly effective and should not be a first line treatment for scabies. It is at best an adjunctive treatment for post-treatment pruritus and an alternative for BBE in infants and pregnant ladies.
6) topical sulphur e.g. 10% sulphur in petrolatum.

2. CRUSTED SCABIES (NORWEGIAN SCABIES)
Crusted scabies is an infestation with Sarcoptes scabiei hominis in which huge number of mites were present. The grossly thickened horny layer is honeycombed with cavities which contain large number of mites, and these are shed into the environment of the patient. Crusted scabies is highly contagious; an undiagnosed case of crusted scabies may lead to large outbreak of common scabies.
2.1. Aetiology and Pathogenesis
In common scabies there are few mites probably because of scratching destroys the burrows. In some patients skin anaesthesia secondary to neuropathy or spinal injury obviously do not perceive itch and do not scratch crusted scabies is likely to develop.
Crusted scabies has a predilection for patients with physical debilitation, mental retardation, sensory impairment and immunosuppression.
2.2. Clinical Features
Masses of horny debris accumulate beneath thickened and discoloured nails. Large warty crusts form on the hands and feet, and the palms and soles may be irregularly thickened and fissured. Itching is often absent or slight. It may present as exfoliative dermatitis. Differential diagnoses include hyperkeratotic eczema, psoriasis, Darier's disease and contact dermatitis.
2.3. Treatment
There is no single treatment for crusted scabies. The general principle is that multiple treatment is needed and sequential use of several agents may be necessary. The following regimen is suggested with the use of 25% benzyl benzoate emulsion (BBE), which is the most commonly used agent in public hospitals in Hong Kong. Ivermectin, given in a single oral dose, is found to be effective in healthy and HIV subjects in a small study.
Equipment to prepare: Soft brushes to apply the BBE, tooth brushes to rub away the scales, nail clipper to trim the nails.
Treatment is intensive and should be given by nurses well informed and dedicated to give the treatment.
BBE is applied from neck include behind the ear down to the toes.
Application to the face and scalp is necessary. BBE may also apply to those area but may be too stinging. 0.5% Malathion is a good alternative which is also effective and causing less irritation. Crotamiton is an alternative to malathion to the area, but is much less effective.
Nails should be cut short. BBE should be scrubbed into the area under the nail.
Scales, which are usually thick under the nail and on flexural area should be gently rubbed away with brushes.
Repeat the above steps for 4 consecutive days at least.
Repeat examination and isolation for mite on day 5. Continue treatment until identification is negative.
Give oral antibiotics which are effective against staphylococcus and streptococcus unless contraindicated, for 7-10 days.
Change clothing and bed linen daily and these are treated in method mentioned below.
Isolation can be stopped when treatment is completed (e.g. day 5 when identification is negative).
Repeat identification procedure one week after treatment is stopped. Repeat scrapings for identification each week as long as the patient is still in ward.
While BBE is cheap and safe, its use in crusted scabies is less reported in the literature. It causes irritant contact dermatitis especially in areas infected or eczematised. The local profile of resistance to BBE is not reported, but since BBE is the most commonly used scabicide locally, resistance to the agent is not surprising. Physician should be prepared for this possibility and ready to use other agents if clinical response is not satisfactory. The microbiologist،¦s opinion is invaluable.
Management of Contacts:
Adequate treatment of contacts is as important as adequate management of the target patient. Success of treatment depends on an all-inclusive approach: all individuals in the ward and their family members should be treated, and treated simultaneously, no matter whether they are symptomatic or asymptomatic.

3. PEDICULOSIS CAPITIS
3.1. Epidemiology
The infection rate was higher in urban than in rural areas. In the early 1980s, there was a resurgence of infection due to the emergence of the so-called 'super-louse' which was resistant to DDT powder.
Lice are more common on children than on adults, and female of all ages are more frequently infected than males. There does not appear to be any direct correlation between hair length and louse infection rates, and it has been suggested that large masses of hair may, in fact, impede transmission of lice from scalp to scalp. The vast majority of head louse infections are acquired by direct head-to-head contact. Spread of lice is encouraged by poverty, ignorance, poor hygiene and overcrowding. Overcrowding is perhaps the most important factor. Transmission of head lice by sharing personal articles such as hair brushes, combs and towels is possible.
3.2. Clinical Features
These occur in the long hair of the scalp, but may also invade eyebrows and eyelashes. The characteristic manifestation of head louse infection is scalp pruritus. Secondary bacterial infection may occur as a result of scratching, and concomitant head louse infection must always be considered in cases of scalp impetigo. Pruritic papular lesions may occur on the nape of the neck, and occasionally a generalized non-specific pruritic eruption develops. In severe, neglected cases pus and exudate may produce matting of the hair.
Nits are egg-cases. They occur in greatest density on the occipital and parietal regions. Most of the unhatched nits are within 5 mm of the scalp surface. The eggs can be distinguished from dandruff by the fact that they are firmly attached to the hair. Moreover, if the affected hair is cut off and observed under microscope, the oval egg capsule can be easily identified. Adult lice and nymphs may be seen in heavy infestation.
3.3. Treatment
Treatment of pediculosis of the scalp aims at the destruction of the lice and the ova. Other members of the family and the whole class of school children should be examined, otherwise re-infestation will occur.
Malathion is effective and has good ovicidal activity. It is adsorbed onto keratin, a process which takes approximately 6 hours, and has a residual protective effect against re-infection for about 6 weeks. Malathion should be left on the scalp for 12 hours before washed off. The insecticide is degraded by heat, and a hot-air dryer should not be used. Treatment should be repeated 2 weeks later when the larvae have hatched out. Lotions are preferable to shampoos, as the latter expose the insects to relatively low concentrations of insecticide which will favour the development of resistance.
Empty egg-cases are difficult to dislodge, they persist for some time until they are gradually worn away by repeated washing. They may be removed with a fine-tooth comb or forceps. A cream rinse containing formic acid may facilitate the removal.

4. PEDICULOSIS CORPORIS
4.1. Incidence and Epidemiology
Pediculosis corporis is now uncommon in developed countries. It mainly affects the poor and neglect and flourishes in overcrowded, dirty situations where individuals seldom change their clothes. There is great variation in the number of eggs and lice on the clothing. In most cases the number of lice is small but in some thousand of lice may be present. Transmission is mainly by direct close body contact or by sharing infested clothing. Lice on a cooling dead body will look for alternate lodgings, and doctors asked to certify death in a vagrant should be aware of this.
4.2. Clinical Features
Intense pruritus is the chief complaint. It is due to sensitization to salivary antigens of the lice. Excoriation with secondary bacterial infection and hyperpigmented changes are common physical findings.
When the lice are not feeding, they stay in the clothing. Therefore, it is important to examine the inner lining of clothing including the seams of underpants.
Hands and feet are usually not involved and there is a predilection for the upper back. The characteristic distribution helps to distinguish it from scabies. The principal louse-borne diseases are epidemic typhus, trench fever and louse borne relapsing fever.
4.3. Treatment
It is the clothing rather than the patients which require treatment. Destruction of the lice is accomplished by laundering or boiling the clothing and bedding. High temperature laundering of underpants and dry-cleaning of outer clothing are also effective. Tumble-drying is the most effective means of killing both lice and eggs.
The patient should bath thoroughly with soap and water. Theoretically, this is sufficient. However, many dermatologists would prescribe gamma benzene hexachloride to treat the body as well. Mass delousing of large number of persons can be carried out successfully by simply blowing DDT powder under the clothing with a hand dust gun.