INFESTATIONS  1. SCABIES 1.1 Morphology and Biology of the Scabies Mite  The female mite measures about 0.4 mm long by 0.3 mm broad, the smaller male measures 0.2 mm long by 0.15 mm board. Copulation occur in a small burrow excavated by the female mite. The fertilized female enlarges the burrow and begins egg-laying. The burrow is lengthened 2-3 mm daily. About 50 eggs are laid by each female mite during her life span of 4 to 6 weeks. The mite shows a preference for certain sites in which to burrow. They appear to avoid a high density of pilosebaceous follicles. The average number of female mite on a patient suffering from scabies is about 12. 1.2 Incidence and Epidemiology The incidence of scabies in developed countries show cyclical fluctuation. It affects all races and social classes world-wide. The interval between the end of one epidemic to the beginning of another epidemic is about 10-15 years. Scabies may occur in any age but it is most common in children and young adults. The overall sex incidence is probably equal. Overcrowding associated with poverty and poor hygiene in under-developed countries encourages the spread of scabies. Transmission is by close physical contact like sharing of a bed. Studies have demonstrated that indirect spread by clothing and bedding is not important. The commonest sources of infection are friends and relatives outside the home. Outside the host scabies mite can survive 24-36 hours at room condition. 1.3 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 are burrows. 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. Burrow 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 microscopical examination. A burrow is gently scraped off the skin with a blunt scapel, 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. 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 it 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 clothings changed which are then laundered in the usual way. After the scabicidal treatment, pruritus may persist for a further 10 days i.e. until the dead mites have been shed in the squames. A topical antipruritic such as crotamiton cream may be applied on residual itchy areas. 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 infants and young children - benzyl benzoate should be diluted with 2 or 3 parts water for use on infants and young children. Prolonged or repeated applications of benzyl benzoate should be avoided. Crotamiton cream may be used to treat burrows on the head and neck. Other drugs used : (i) gamma benzene hexachloride (Lindane) - a single application wash off after 12-24 hours is usually recommended. (ii) malathion - malathion 0.5% in aqueous base has been used as scabicide. It should be left on the skin for 24 hours. (iii) permethrin - 5% dermal cream employed as a single application, wash off 8-12 hours. (iv) monosulfiram - 25% solution diluted with 2-3 parts of water to be applied daily for 2 or 3 days. (v) topical thiabendazole. (vi) crotamiton. 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. An undiagnosed case of crusted scabies may cause 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. In some patients physical disability like paresis or severe arthropathy the main reason for the development of crusted scabies is probably a physical inability to scratch in response to itching. Crusted scabies has also resulted from inappropriate use of potent fluorinated topical steroids. 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. Differential diagnosis include hyperkeratotic eczema, psoriasis, Darier's disease and contact dermatitis. 2.3 Treatment Treatment is as for ordinary scabies although several application of a scabicide may be needed. 3. PEDICULOSIS CAPITIS 3.1 Incidence and Epidemiology In 1975 a survey of schoolchildren in England showed an overall prevalence of 2.44%. 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 is 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. There are conflicting opinions about the role of fomites in transmission of head lice, and in practice the involvement of caps, scarves, combs and brushes is difficult to confirm or refute. 3.2 Clinical Features These occur in the long hair of the scalp, but may also invade eyebrows and eyelashes. The characteristics 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" - which are the empty egg-cases are easily identified, and occur in greatest density on the occipital and parietal regions. Adult lice and nymphs may be seen easily in heavy infections. 3.3 Treatment Treatment of pediculosis of the scalp aims at the destruction of the pediculi and the ova. Contacts should also be treated which will involve treating a whole class of school-children. The acetylcholinesterase-inhibiting insecticides malathion is efficient pediculicide and have good ovicidal activity. Malathion 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 remain 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. Oral treatment with cotrimoxazole and topical crotamiton lotion have been used for the treatment of pediculosis capitis. 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, unhygiene 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 Majority of patients have itchiness as their chief complaint. Itchiness is the consequence of sensitization to louse salivary antigens. In some cases who have not become sensitized or have acquired tolerance to the bites are asymptomatic. Excoriation with secondary bacterial infection and hyperpigmented changes are common physical findings. When the lice are not feeding they live in the clothing, so the inner lining of clothing include the seams of underpants must be searched carefully for nits. It is differentiated from scabies by the freedom of hands and feet from involvement and its predilection for the upper back. Pruritus and urticaria may cause some confusion. The principal louse-borne diseases of man 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. Mass delousing of large numbers of persons can be carried out successfully by simply blowing DDT powder under the clothing with a hand dust gun.