Scabies (the itch)
Scabies is a highly irritant condition occurring on the skin of an individual sensitized to the female mite of Sarcoptes scabiei or its products.
MODE OF TRANSMISSION
Transmission is by skin-to-skin contact with an affected individual and usually occurs in bed. Holding hands is a less common mode of spread from infested children, as warmth is necessary for the mite or acarus to remain mobile.
Most individuals will only harbour about a dozen mature female acari. However, many thousands of mites may be associated with crusted or Norwegian scabies, and the affected individuals seem unable to mount the same sensitizing responses. This condition is more common in the mentally subnormal and immunocompromised individuals.
Sites of predilection for burrows include the finger webs, wrists, elbows, ankles, breasts and genitalia. Linear or curved tracts may be seen with a tiny vesicle at one end that contains the mite. The mite can be removed on the end of a needle, or the burrow scraped to reveal eggs, mite fragments or faeces as firm evidence of infestation.
Sensitivity to the mites’ products occurs after 4-6 weeks, when individuals develop most commonly a widespread, highly irritant, excoriated and often secondary infected folliculopapular eruption. Secondary eczematous changes may be evident, or the patient (especially a child) may present with impetigo.
The diagnosis should be suspected if symptoms of itching are severe, when papules appear over genitalia and the history indicates that bedfellows, family or friends are also complaining of irritation. Infants develop papules on the palms, soles or the axillary folds and some adults suffer postscabetic papules for up to several months after sensitization. Mites from dogs or birds may produce vesicular lesions, crusting or urticaria but infestation from these sources is not associated with burrows.
All infested individuals and their close contacts should be treated. A lotion containing gamma-benzene hexachloride (lindane 0.1-1%) must be applied to all parts of the skin surface save the face and kept in contact with the skin for a full 24 hours, so that hand-washing must be followed by reapplication. The process is then repeated 24 hours later and all personal garments, night attire and bed-linen should then be laundered in a washing machine. Neurotoxic effects from the absorption of lindane in young children occasionally occur and malathion or permethrin should be used instead.
Pediculosis capitis (head lice)
This condition is prevalent in schoolchildren in the UK, with infestation also occurring (though less commonly) in those who have close contact with the children, e.g. mothers. The head louse itself is difficult to find within a thick head of hair but evidence of its presence is seen in the many eggs or ‘nits’ laid along the hair shafts. The initial lesions occur close to the scalp, especially over the occipital region and the nape of the neck. In children, infestation should be suspected when excoriation is seen and impetigo is evident around the hair margin. Infestation occurs from the close touching of heads and is
often widespread within a class of schoolchildren.
Malathion 0.5% and carbaryl are often used because of lindane-resistant strains of lice. These drugs are left on for 12 hours overnight and removed with shampoo (repeated twice at intervals of 3 days). Cutting the hair facilitates the use of local applications. Eggs are killed by this treatment and it is not necessary to continually attempt to remove them.
Pediculosis corporis (body lice)
This condition is usually found only in those with a gross lack of hygiene, such as vagrants. The skin of affected individuals is often thickened, pigmented and excoriated; lice, often few in number, may be evident on the seams of clothing worn next to the skin. The clothes should be autoclaved.
Pediculosis pubis (pubic lice)
Infestation is evident over the pubic hair, with occasional spread in hairy individuals on to the body or even the eyebrows. Contracting the disease is often related to promiscuity. Irritation is the initial symptom and patients are able to detect movement of the louse on skin covered by relatively sparse hairs. Treatment of the infestation is the same as that for head lice.
Development of these diseases depends on contact with the animals or birds that form the primary host for the causative organisms. These include Cheyletiella, most commonly C. yasgouri or C. parasitovorax; from dogs, cats, rabbits and other pets. On close inspection of their coats such animals will often have evidence of scaling and thickening of the skin, on which mites are sometimes evident by their movement. Brushings are taken on to dark paper, which is then scanned for evidence of mites, fleas or their products. Bites should be suspected in those who have close contact with animals; the area of skin affected shows grouped vesiculopapular lesions.
This must begin with the elimination of the arthropod at its source. All other manoeuvres that attempt to produce symptomatic relief of itching associated with bites, such as repellants, calamine lotion, cream or antihistamines, give only temporary relief.