What is scabies?

(Revised on February 12, 2015)

Scabies is a disease in which itch mite (Sarcoptes scabiei) parasitizes the outermost layer of the skin, the stratum corneum, and is transmitted from person to person. There are keratinized scabies (scabies) in which a large number of mites are infested, and normal scabies (usually scabies), which is a minor infestation but is accompanied by severe itching (Table 1) . In recent years, cases of outbreaks have been increasing in hospitals, facilities for the elderly, nursing homes, etc. in Japan, and manuals for preventing scabies infection have been created, but there is confusion in prevention and treatment methods, and medical care and long-term care It is a problem among the parties concerned.

Transmission route

Itch mite is vulnerable to dryness and dies in a few hours when separated from the skin. Accidental cases of animal scabies such as dogs and raccoon dogs have been reported, and infected people show skin symptoms, but because mites do not propagate in the skin, they end up with temporary infestation. The number of scabies patients is estimated to be 80 to 150,000 per year. Most of the transmission routes are human-to-human contact. Therefore, in addition to family members, caregivers, and sex partners, there is a possibility of infection by dance partners, mahjong friends who perform with kotatsu, and sleeping on tatami mats. In rare cases, it may be transmitted from bedding or clothing. Itch mite moves slowly at temperatures lower than human body temperature, and hardly moves at 16 ° C. In normal social life, sitting side by side with a scabies patient for several hours is unlikely to cause infection. Immediately after infection, there are no symptoms at all, but about 4 to 6 weeks after infection, a large number of mites grow and are sensitized by their worms, molting shells and excrement (feces), resulting in severe itching as an allergic reaction. Begins. When infected from a patient with keratinized scabies, a large number of mites are transferred, so the incubation period is very short, 4 to 5 days. In welfare facilities for the elderly and nursing homes where group life is carried out, there is a risk of outbreaks when one patient with keratinized scabies is admitted. In 1996, a questionnaire survey on the outbreak of scabies was conducted at 506 nursing homes and special nursing homes in Tokyo, Kanagawa, Chiba, and Saitama prefectures. Nursing homes accounted for 45%, and special nursing homes accounted for 79%. Most were outbreaks of 10 or less, but there were also 5 outbreaks of 41 or more. The duration of development of patients was 89% for 1 to 6 months, 8.2% for 6 months to 1 year, and 2.6% for 1 to 2 years, and one facility was found for more than 2 years (skin disease treatment 19: 468, 1997). .. Her situation hasn't changed much even now.

Clinical symptoms / diagnosis

Severe itching can increase, especially at night, and disturb sleep. However, elderly people and patients with keratinized scabies may have less complaints of pruritus. The characteristic rash of scabies is the scabies tunnel (small raised brown tone, winding linear rash), which is found on the flexion side of the wrist, palm ulnar side, fingers, fingers, elbows, and Achilles tendon. In addition, papules, blisters, crusts, and nodules are also seen. Nodules may be found in the scrotum. In addition, papules may be found in the lower abdomen, back, and axilla, so it is necessary to observe him all over the body. The definitive diagnosis of scabies is the detection of itch mite. However, the detection rate of itch mite from patients suspected of having scabies due to interviews and skin symptoms is around 60% even when performed by a dermatologist, and improvement of the detection rate depends on the efforts of the attending physician. Therefore, if you have a suspicious rash with severe pruritus, seek medical attention from a dermatologist at an early stage. Even if the test is negative, it is necessary to repeat the test several weeks before the pruritus and skin symptoms subside. The method of detecting itch mite is to observe the tip of the scabies tunnel with a magnifying glass (dermoscope, eyepiece of a microscope, etc.). Can be observed. Also, cut off the tip of the scabies tunnel or rash with a curved ophthalmic scissors, or place a piece of tissue collected by rubbing the surface of the rash with a scalpel on a slide glass, and apply 20% potassium hydroxide solution to a small piece of skin. Drop it into the scabies, allow it to pass through, and inspect it under a microscope. In addition to insect bodies and eggs, some insect bodies and egg shells are detected. Blood images, blood biochemical examinations, etc. are normal. No immunological test has been developed.

Keratinized scabies (scabies, crusted scabies)

The scales and scabs that have fallen off the patient have a large number of itch mite, which makes them a source of outbreaks. Patients with keratinized scabies have various underlying diseases such as motor dysfunction / disorder or immunological abnormalities that are often seen in the elderly, and systemic administration such as oral administration and injection of steroids and external use are also becoming more severe. It contributes to. In the keratinized type, the nails are also affected, and pruritus is indefinite and resistant to treatment. Since itch mite is easy to detect in the keratinized type, it is diagnostically important to diagnose a characteristic rash and suspect scabies.

Treatment / prevention

Drinking medicines and ointments aimed at killing itch mite are used (Table 2) . Apply the ointment to the entire body below the neck so that there is no leftover, including normal areas. For itching, use an oral medicine to prevent itching. ≪Drugs≫ Take ivermectin on an empty stomach. ≪Ointment≫ There are phenothrin lotion, sulfur agent, crotamiton cream, and benzyl benzoate. However, the consent of the patient or substitute is required when using benzyl benzoate. In addition, γ-BHC should not be used due to the relationship with the Stockholm Convention on Persistent Organic Pollutants. Early detection of patients is important to prevent the spread of infection, and if scabies is suspected, ask a dermatologist for examination at an early stage. It is necessary to carry out tests even for asymptomatic patients. In addition, in the event of an outbreak, it is necessary to identify the source of infection at the facility, such as patients with keratinized scabies, and to inspect residents and staff who have had the opportunity to become infected.

Isolation is not necessary because there is no risk of infection if the skin is not in direct contact with normal scabies patients, but keratinized scabies patients should be managed in a private room for a short period of time and efforts should be made to prevent infection. Also, in the case of keratinized scabies, the number of mites is extremely large, so there is a possibility that mites may be present in the linen, blankets, duvets, bed his domats, etc. used by the patient. In one study, bedding that the patient directly touched was soaked in hot water above 50 ° C for at least 10 minutes or a large dryer, as it is said to survive for 3 days at 25 ° C and 90% humidity. It is possible to kill all mites by treating with 20-30 minutes.

(National Institute of Infectious Diseases Hansen's Disease Research Center Norihisa Ishii Faculty of Infectious Diseases and Medical Sciences Kyoko Sawabe, Mutsuo Kobayashi)