The Topic of This Month Vol.22 No.10(No.260)

Scabies, caused by skin infestation with a human itch mite (Sarcoptes scabiei ), has been recognized as a sexually transmitted disease. Recently, it has become a serious problem among medical staffs and nursing helpers as its outbreaks have been on the increase in hospitals and homes for the aged and handicapped individuals.

The following is a summary of the problems involved in examination, treatment, countermeasures and the prevention of scabies outbreaks in helping toward the better understanding of those concerned and for the future control proposals of scabies.

The scabies mite and the mode of transmission

An oval disk-shaped female adult of the scabies mite has body length of 400µm and width of 325µm. The size of a male adult is about 60% that of a female. The mite grows up from egg→larva→nymph→adult in roughly two weeks. Since the larvae, nymphs and male adults wander freely over the human skin, bury themselves in the cornified epithelium, or hide themselves in the hair follicles, it is difficult to locate their shelters. The male adults look for females in the cornified epithelium to mate with. A female adult after mating keeps on burrowing in the cornified epithelium and lays 2-4 eggs a day in the tunnel for 4-6 weeks to the end of its life. The mite is vulnerable to drying and dies within 2-3 hours after it no longer has a direct contact with the skin (see p. 246 of this issue). Animal scabies caused by a variant of S. scabiei is also known in Japan (see p. 247 of this issue). It might produce a complex of symptoms resembling those of typical human scabies by accidental infestation, but it is only a transient infestation since they do not fertilize in the human skin.

Transmission occurs mostly through close physical person-to-person contact. Therefore, family members, helpers, or sexual partners as well as dancing partners, mah-jongg playmates played on "kotatsu" (a warmer covered with a quilt) are infested. Transmission might take place also when people sleep in huddle on "tatami" and rarely from bedclothes or clothes. Since scabies mites do not move actively below the human body temperature, the possibility of acquiring infestation by sitting with a patient side by side for a few hours in ordinary social life is very low. A period of 4-6 weeks often elapses before onset of itching, which develops as an allergic response to the mite bodies or their feces.

At a nursing home for the aged or handicapped individuals, where people live together, admission of an infested person might result in an outbreak. In April 1996, Ohtaki N. conducted a questionnaire survey by mail of 506 nursing homes and extended care facilities for the aged in Tokyo, Kanagawa, Chiba, and Saitama Prefectures. The responding rate was 64%, and the answer letters from 45% of the former and 79% of the latter indicated experiences of scabies outbreaks in the past (Fig. 1). Most of these outbreaks involved 10 or fewer cases, but those involving more than 41 cases were reported from five facilities. The duration of outbreaks was 1-6 months in 89%, 6 months to one year in 8.2%, one to 2 years in 2.6%, and longer than 2 years in one facility (Hifubyoh-Shinryoh 19:468, 1997).

Clinical symptoms and diagnosis

There is severe itching, especially at night, which causes sleep disturbance. In some elderly patients, however, itching is much less pronounced. Burrows in the cornified epithelium are the characteristic lesions of scabies. They appear as fine, tortuous, blackish threads on the flexor surfaces of the wrists, the palms, the palmer and lateral aspects of fingers, the web spaces between fingers, the elbows, and the Achilles' heels. Papules, tiny vesicles, scabs, and small nodules are also seen. Since small nodules might develop on the genitals of man and papules only on the lower portion of the abdomen, dorsum back and the axilla, careful examination of the whole body is necessary.

A definitive diagnosis of scabies can be made only by demonstration of the scabies mites from skin specimens. Since the rate of detection of the mite from cases suspected of scabies from their complaining itch and dermal symptoms is about 60% according to dermatologist tests (Fig. 2), improved mite detection is dependent on the efforts of the physicians in charge. Therefore, if peculiar rash with intense itching is found, the physician should request a medical dermatology specialist for further examination. Even if it turned out to be negative, examinations at a few weeks' interval are necessary until itching and other dermal symptoms have subsided.

For histological examinations of scabies patients, an epidermal biopsy specimen of a papule or an entire burrow is taken with curved ophthalmic scissors or a biopsy specimen is taken by scraping the surface of a papule with a scalpel. The specimen is placed on a slide glass and examined under a microscope after dropping a 20% potassium hydroxide solution to increase the transparency of the tissue. Not only the mite bodies or their eggs, but also various accessories of mites are detected. The blood picture and the blood biochemistry data are normal. No serological test is available.

Crusted scabies (Norwegian scabies)

Crusted scabies is a severe form caused by infestation with an extraordinarily large number of mites. The mite-infested areas are covered with grayish-white or yellowish-white thick keratotic crusts, sometimes with fissures. The mite population of ordinary scabies is a few dozens, but it is reported to be one or two millions in crusted scabies. Since there are a number of scabies mites in scales or crusts exfoliated from patients, they might cause outbreaks. Crusted scabies cases may have such underlying conditions as disability of movement, which is often seen in aged persons, or immunological abnormality. Oral administration, injection or topical application of corticosteroids may result in worsening the disease. Crusted scabies, affecting also nails, shows itching of variable intensities and is resistant to treatment by anti-mite drugs. Scabies mites are easily isolated from crusted scabies cases; nevertheless no examination would be conducted unless scabies is suspected when characteristic rash is observed.

Treatment and prevention

Currently used anti-scabies medicines are shown in the Table (see p. 244-245 of this issue). Sulfur-containing preparations are only available drugs approved by health insurance coverage in Japan, but ointment and lotion are only feebly effective and not well accepted. Sulfur-containing bath is to some extent effective, but frequent bathing or high concentration of sulfur might cause roughing of the skin. The current preferable treatment is application of crotamiton ointment. It is important to apply the lotion or the ointment to the whole body from neck to toes, including the hands, fingers and genitals. Since these are only feebly effective and laborious to apply, highly effective oral ivermectin is eagerly desired, and approval of commercialization of such drugs and that of health insurance coverage are expected. For itching, antihistamines are orally administered. In crusted scabies, it is necessary to remove thick scabs.

If scabies is misdiagnosed as other dermatological conditions and treated with corticosteroid liniment, rash and itching might temporally heel but will worsen before long. Corticosteroid ointment should be avoided for treating scabies. To prevent the spreading of infection, early diagnosis is important. When scabies is suspected, request a dermatologist for examinations, and if one patient is diagnosed, his or her family members or those who stayed together, even if asymptomatic, should also be examined. If an outbreak occurs, the source of infection in the facility such as a case of crusted scabies should be identified and admitted persons and staff members who might have had chances of infestation should also be examined. If avoidance of skin-to-skin contact with cases of typical scabies is feasible, isolation of cases is not necessary. Crusted scabies cases, however, should be isolated from others, and care must be taken to prevent infestation when such patients are treated (see p. 243 of this issue).

Future problems

There has been no nationwide survey for current status of scabies in Japan; such a survey should immediately be conducted. In addition, it is necessary to give developmental education on scabies to physicians, nurses and helpers and to make efforts for early diagnosis and treatment and for prevention of outbreaks. It is also necessary to be careful on outbreaks in facilities for not only the aged but also for infants and children. More attention should be paid to prevent such immune-depressed cases as AIDS patients from scabies. Since it is not easy to obtain highly effective medicines nowadays, it will take more than several months for alleviation once scabies starts to spread to patients, admitted persons, medical personnel and helpers in a hospital or facility. An outbreak of scabies will inflict a great loss to the facility involved, e.g., the loss of the facility's reputation. To solve these problems in a short notice, responsible people should immediately direct their efforts on highly effective drugs and to make them available in Japan.

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