Scabies

Human scabies is caused by an infestation of the skin by the human itch mite (Sarcoptes scabiei var. hominis). The microscopic scabies mite burrows into the upper layer of the skin where it lives and lays its eggs. The most common symptoms of scabies are intense itching and a pimple-like skin rash. The scabies mite usually is spread by direct, prolonged, skin-to-skin contact with a person who has scabies. An infested person can spread scabies even if he or she has no symptoms. Humans are the source of infestation; animals do not spread human scabies.

Scabies occurs worldwide and affects people of all races and social classes. Scabies can spread rapidly in crowded conditions where close body contact is frequent. Institutions such as nursing homes, extended-care facilities, and prisons are often sites of scabies outbreaks

Sexual transmission: transmission is more likely to occur when partners spend the night together than with a brief sexual encounter.

Nonsexual transmission: possibly from sleeping in infested bedding, wearing infested clothing, even routine contact such as shaking or holding hands. Transmission from a toilet seat may be possible, but is unlikely.

The female mite burrows under the skin and begins laying eggs within hours (two to three eggs daily). The eggs hatch and become adult mites within 10 days. Symptoms, primarily itching, appear approximately four weeks from the time of contact as a result of sensitization to the presence of immature mites.

A person with scabies is considered infectious as long as they have not been treated. Infested pieces of clothing and bedding are considered infectious until treated. After treatment, a person may unknowingly reinfest themselves by coming into contact with the same person who had scabies to begin with or with someone else who has scabies.

The most common symptoms of scabies, itching and a skin rash, are caused by sensitization (a type of “allergic” reaction) to the proteins and feces of the parasite. Severe itching (pruritus), especially at night, is the earliest and most common symptom of scabies. A pimple-like (papular) itchy (pruritic) “scabies rash” is also common. Itching and rash may affect much of the body or be limited to common sites such as:

• Between the fingers
• Wrist
• Elbow
• Armpit
• Penis
• Nipple
• Waist
• Buttocks
• Shoulder blades

The head, face, neck, palms and soles often are involved in infants and very young children, but usually not adults and older children.

Tiny burrows sometimes are seen on the skin; these are caused by the female scabies mite tunneling just beneath the surface of the skin. These burrows appear as tiny raised and crooked (serpiginous) grayish-white or skin-colored lines on the skin surface. Because mites are often few in number (only 10-15 mites per person), these burrows may be difficult to find. They are found most often in the webbing between the fingers, in the skin folds on the wrist, elbow or knee, and on the penis, breast or shoulder blades.

Diagnosis of a scabies infestation usually is made based upon the customary appearance and distribution of the rash and the presence of burrows.

Whenever possible, the diagnosis of scabies should be confirmed by identifying the mite or mite eggs or fecal matter (scybala). This can be done by carefully removing the mite from the end of its burrow using the tip of a needle or by obtaining a skin scraping to examine under a microscope for mites, eggs or mite fecal matter (scybala). However, a person can still be infested even if mites, eggs or fecal matter cannot be found; fewer than 10-15 mites may be present on an infested person who is otherwise healthy.

It is important to remember that the first time a person gets scabies they usually have no symptoms during the first two to six weeks they are infested; however they can still spread scabies during this time.

In addition to the infested person, treatment also is recommended for household members and sexual contacts, particularly those who have had prolonged direct skin-to-skin contact with the infested person. Both sexual and close personal contacts who have had direct prolonged skin-to-skin contact with an infested person within the preceding month should be examined and treated.

All persons should be treated at the same time to prevent reinfestation.

Products used to treat scabies are called scabicides because they kill scabies mites; some also kill mite eggs. Scabicides used to treat human scabies are available only with a doctor’s prescription. No “over-the-counter” (non-prescription) products have been tested and approved to treat scabies. The instructions contained in the box or printed on the label always should be followed carefully. Always contact a doctor or pharmacist if unsure how to use a particular medicine.

Scabicide lotion or cream should be applied to all areas of the body from the neck down to the feet and toes. In addition, when treating infants and young children, scabicide lotion or cream also should be applied to their entire head and neck because scabies can affect their face, scalp, and neck, as well as the rest of their body. The lotion or cream should be applied to a clean body and left on for the recommended time before washing it off. Clean clothing should be worn after treatment.

Bedding, clothing and towels used by infested persons or their household, sexual and close contacts (as defined above) anytime during the three days before treatment should be decontaminated by washing in hot water and drying in a hot dryer, by dry-cleaning, or by sealing in a plastic bag for at least 72 hours. Scabies mites generally do not survive more than two to three days away from human skin.

Because the symptoms of scabies are due to a hypersensitivity reaction (allergy) to mites and their feces (scybala), itching still may continue for several weeks after treatment even if all the mites and eggs are killed. If itching still is present more than two weeks to four weeks after treatment or if new burrows or pimple-like rash lesions continue to appear, retreatment may be necessary.

Skin sores that become infected should be treated with an appropriate antibiotic prescribed by a doctor.

Use of insecticide sprays and fumigants is not recommended.

• Abstinence (not having sex) is the best form of prevention.
• Mutual monogamy (having sex with sex with only 1 uninfected partner who only has sex with you) is effective.
• Limit the number of sexual partners to reduce exposure to all STDs.
• Use latex condoms for all types of sexual penetration (oral, vaginal, anal). Note: Latex condoms, when used consistently and correctly, can reduce the risk of transmission of other STDs, but are not considered effective against scabies.
• Know your partner(s). Careful consideration and open communication between partners may protect all partners involved from infection.
• Have regular check-ups if you are sexually active.
• If you have an STD, don't have sex (oral, vaginal, or anal) until all partners have been treated.
• Prompt, qualified, and appropriate medical intervention and treatment and follow-up are important steps in breaking the disease cycle.

• Secondary bacterial infections may be caused by aggressive scratching.
• Scabies is not usually known to cause anything more than discomfort and inconvenience.

HIV/STD Hotline 800-243-2437 (TTY 800-782-0423)

• US Centers for Disease Control and Prevention
• American Sexual Health Association