Scabies is due to invasion of the epidermis by a mite Acarus scabiei (Sarcoptes scabiei var. hominis). The adult female is the form in which the mite is usually isolated and is approximately of an inch in length—just visible to the naked eye; the male is about half this size. Successful infection of a new victim is accomplished by a newly fertilized female which moves over the warm body at about 1 inch a minute until it selects a site for burrowing. This therefore requires fairly prolonged contact with an infected person and infection may be spread in hand holding games at school, as with a ‘venereal infection’ and particularly between members of a family. Having burrowed into the horny layer of the skin the female remains in the burrow for the rest of her life. Two or 3 eggs a day are then layed for several weeks as the mite burrows along the skin. The eggs hatch in 3 to 4 days, the larvae then leaving the burrow and sheltering in hair follicles. The nymphs moult to give rise to the adult form. Mating occurs on the surface of the skin and the cycle recommences, the whole cycle from egg to oviparous female taking 14 days.
The mites burrow in certain parts of the body, the majority being found on the hands and wrists. The burrows are most visible on the sides of the fingers or the flexor aspects of the wrists. The other area in which burrows are most commonly found is the sole of the foot; they may also be found on elbows, buttocks an axillae. On the penis and scrotum the burrow is obliterated in an inflammatory nodule and such lesions in an itchy patient are virtually diagnostic. Similar nodules resembling small abscesses also appear scattered over the trunk in infants. In these areas there are very few acari and the average number on a sufferer is about 12; as 60 per cent of these are to be found on hands and wrists this is obviously the area to search first for bu:rows.
When the mite first burrows into the skin of a patient who has never before had scabies the infestation remains symptomless for about a month. After this an erythematous reaction occurs round the burrows, a papular urticarial eruption appears on the forearms, axillary folds, waist, inner thighs, buttocks and round the ankles. The patient then commences to itch, the irritation being most severe when warm in bed at night. This stage appears to be one of sensitisation of the host and in the presensitisation phase the host acts as a symptomless carrier. When such a sensitised patient acquires scabies on another occasion he develops a reaction within a few hours to the entry of the mite and may therefore scratch it out before further infestation can occur, thus developing a type of immunity by sensitisation.
The degree of reaction which follows sensitisation varies and when severe can cause vesiculation on the hands and feet, especially in children and a scratched eruption which may sometimes become eczematous on the limbs and trunk. If secondary pyogenic infection occurs, pustules and boils appear on the affected areas and it is not uncommon to see large ecthymatous ulcers on the buttocks.
In adults the rash is confined to trunk and limbs but in young babies lesions may appear on the face and scalp.
The distribution of the rash, the intense itching and the usual story of other affected members of the family should suggest the diagnosis, which can then be confirmed by isolating an acarus. A watchmaker’s lens for magnification leaves both hands free: a good light and an ordinary pin are necessary. A search should be made on hands, wrists and feet until a burrow is found. At-the anterior end of the burrow the mite is visible as a white oval with a black dot at its front. The burrow in this area is opened with the pin point and the acarus can easily be induced to adhere to the pin. Placed on a slide, a ring of ink round it makes it easier to find under the microscope, where it is not only satisfying evidence of a correct diagnosis but also a horrifying inducement to the patient to carry out treatment with meticulous care.
In mental defectives and psychotics infestation with the acarus becomes overwhelming, possibly because of a diminished sense of itching and therefore little scratching. In these patients the epidermis becomes thickened, crusted and infected and can be seen to be teeming with mites on biopsy even though actual burrows may be obliterated by infection and hard to find. Such cases may be diagnosed as eczema or even exfoliative dermatitis until they become recognised as the source of scabetic infection in others.
Treatment Before carrying out treatment the nature of the infection should be explained to the patient and the importance of all in the household being treated whether yet itching or not.
On the first day a bath should be taken. After drying the skin benzyl benzoate lotion is applied to the whole body from the neck down, preferably with a paint brush by someone else, care being taken to cover every inch especially round hands and feet. This is allowed to dry and the same clothes then reworn.
On the second day the same procedure. On the third day, after bathing and painting, clean clothes should be worn and the dirty clothes washed or sent to the cleaners. Clean bedclothes should also be used.
Stoving clothes is not necessary and it is probable that the impregnation with benzyl benzoate which the dirty clothes receive is sufficient to kill any wandering acari. Nevertheless, such a routine impresses upon the patient the need for care in treatment.
Itching should cease within a week and no more benzyl benzoate should be used, though if the itching subsides slowly calamine lotion with 1 per cent phenol may be used to allay this. In babies and young children benzyl benzoate lotion applications sting unbearably and, when the family includes these, monosulfiram lotion (Tetmosol) should be used in the same routine as benzyl benzoate on all members of the family. Nodules on the scrotum and trunk may be persistent and itchy and can be controlled with crotamiton cream (Eurax).
Scabies varies in its incidence over the years and from 1935 until the outbreak of war, scabies was already on the increase and wartime conditions determined its further spread. After the war it died out, until by 1950 it had become almost a rare disease. Since the mid 1960s there has been a steady increase in its incidence which has now reached worldwide epidemic proportions. It is possible that su^h fluctuations depend on the lowered incidence of sensitised individuals and the increase in non-immune carriers, institutions of various types acting as reservoirs of infection.
The head louse, although indistinguishable from the body louse localises to the scalp and its incidence is still remarkably high among school children in industrial areas where 15 to 20 per cent may be infested in the poorer areas of towns. The present vogue for lacquered piled hair, which may be undisturbed for weeks, and long hair in males is spreading this infestation among an older age group. Often infestation is symptomless, the clue being the presence of nits on the hair shafts. They are seen best with a magnifying glass as shiny, pearl-coloured, oval bodies with a cuff which embraces the hair shaft. In mild infestations the adult louse may not be found, but in more severe cases itching is intolerable the scalp becomes secondarily infected, dotted with impetiginous crusts or even oozing over the whole scalp. The lymph nodes in the posterior triangles of the neck become enlarged and tender and usually in such cases the lice can be seen in the scalp. Sometimes a papular urticarial eruption may be present on the upper trunk or, more misleadingly, this may be a macular erythematous rash.
Treatment. The scalp should be soaked with malathion 0-5 per cent lotion (Prioderm) and left to dry naturally. After 12 hours the scalp is shampooed and combed with a Durbac comb while wet. The process is repeated in 7 to 9 days. In cases where the scalp is secondarily infected an antibiotic cream is applied to the scalp when the hair has been dried after shampoo. It is rarely necessary to cut the hair.
Body lice are rarely seen in this country except in vagrants and unwashed eccentrics. The patient complains of generalised itching and the trunk and limbs are covered with excoriations and, in longstanding cases, pigmented. The lice are more likely to be found in the clothes than on the body and the best way to make the diagnosis is to search the seams of the clothes where collections of the small pearly eggs are to be found.
Treatment. The patient should be bathed and calamine lotion with 1 per cent phenol applied to relieve the itching. The clothing should be dusted with D.T.T. powder to prevent spread of the lice, then placed in a bag and sent for disinfestation by washing or stoving.
The crab louse affects the pubic hair causing intense itching in the genital area. It may also spread to other body hairs. In adults it spreads as a venereal infection.
Treatment. The affected areas should be washed for three successive days in gamma benzene hexachloride (Lorexane shampoo).
Many children after infancy and before puberty suffer attacks of papular urticaria. The lesions are small, round, shotty wheals which may blister, commonly called ‘heat spots’, often ascribed to food allergies, they are in fact what they look like—multiple insect bites. A careful search will usually show lines of lesions along which the insect has fed.
Reactions to insect bites vary according to the degree of sensitivity of the sufferer. Infants are not sensitised and show little reaction; the sensitised adult produces an itchy urticarial lump within half-an-hour of being bitten. Between these two stages is one of delayed hypersensitivity in which the reaction to a bite is delayed 48 hours and then produces a persistent urticarial papule which may not only last for many days but may be followed by a flare of activity in other previous insect bites. For this reason the lesions may be profuse.
Diagnosis. Allergic urticaria is unusual in childhood and its transient wheals which fade without trace are unlike the crusted papules of papular urticaria. When more than one child in a household is affected the condition may be confused with scabies but it is uncommon to see papular urticaria round the hands and wrists, whereas a careful search in these areas will eventually reveal a scabies burrow from which an acarus can be prized. On the lower limbs large bullae may occur especially in girls. Other bullous diseases are uncommon in children and the only other bullous lesion likely to be seen is erythema multiforme which predominantly affects the upper limbs.
Just as demonstration of the acarus in scabies puts the diagnosis beyond argument so does demonstration of fleas from the domestic dog or cat allay the resentment with which the diagnosis of insect bites is often received. The parents should be instructed to brush the dog or cat over a sheet of black polythene and bring the brushings and hairs for inspection, when a search with a magnifying glass or microscope will usually be rewarding.
Treatment. Removal of the source of insects is the only cure. If this is the family dog or cat it should be dusted with an insecticide and any chairs or rugs on which it may have sat should be similarly dusted and vacuum cleaned. In the autumn midges in the garden, in the summer sand fleas at the seaside, mites from the family budgerigar, mites from birds’ nests in the eaves of the house are all possible sources which must be eliminated. Where these are outside sources and uncontrollable the child can be protected with an insect repellant cream containing dimethylphthallate when it goes out to play. For crusting lesions antihistamines are of little value and the antipruritic effect of 1 per cent phenol in calamine lotion is useful.