April 16, 2007

Parasitic Skin Infections


Most skin parasites are tiny insects or worms that burrow into the skin and make their home there. Some parasites live in the skin for part of their life cycle; others would be permanent residents

Creeping Eruption
Creeping eruption (cutaneous larva migrans) is a hookworm infection transmitted from warm, moist soil to exposed skin.

This infection is caused by a hookworm that normally inhabits dogs and cats. The eggs of the parasite are deposited on the ground in dog and cat feces. When bare skin touches the ground, which happens when a person walks barefoot or sunbathes, the hookworm gets into the skin. Starting from the site of infection—usually the feet, legs, buttocks, or back—the hookworm burrows along a haphazard tract, leaving a winding, threadlike, raised, red rash. The eruption itches intensely.

A liquid preparation of thiabendazole applied to the area effectively treats the infection. Thiabendazole or ivermectin given by mouth also is effective.

Lice infestation
Lice infestation (pediculosis) is a skin infestation by tiny wingless insects.

Lice are barely visible wingless insects that spread easily from person to person by body contact and shared clothing and other personal items. Three species of lice inhabit different parts of the body.

Head lice infest the scalp hair. The infestation is spread by personal contact and possibly by shared combs, brushes, hats, and other personal items. Head lice are a common scourge of school children of all social strata. Head lice are less common among blacks.

Body lice usually infest people who have poor hygiene and those living in close quarters or crowded institutions. They live in the seams of garments that are in contact with the skin.

Pubic lice ("crabs"), which infest the genital area, are typically spread during sexual contact. These lice may infest the chest hair, underarm hair, beard hair, eyebrows, and eyelashes as well.

Symptoms and Diagnosis

Lice infestation causes severe itching in the infested area. Intense scratching often breaks the skin, which can lead to bacterial infections. Children may hardly notice head lice or may have only a vague scalp irritation.

Lice themselves are sometimes hard to find, but their eggs are readily apparent. Female lice lay shiny grayish white eggs (nits) that can be seen as tiny globules firmly stuck to hairs near their base. With chronic scalp infestations, the nits grow out with the hair and therefore can be found some distance from the scalp, depending on the duration of the infestation.

Nits are distinguished from other foreign material present on hair shafts by the fact that they are so strongly attached. Adult body lice and their eggs also may be found in the seams of clothing worn close to the skin.


Several effective prescription and nonprescription drugs are available to treat lice. Nonprescription shampoos and creams containing pyrethrins plus piperonyl butoxide are applied for 10 minutes and are then rinsed out. Prescription permethrin, applied as a liquid or as a cream, is also effective. Lindane —a prescription drug that can be applied as a cream, lotion, or shampoo—also cures lice infestation but is not as effective as the other preparations and is not recommended for children because of possible neurologic side effects. Prescription malathion, although highly effective at killing both adult lice and eggs, is not considered a first line of treatment because it is flammable, has an objectionable odor, and must remain on the skin for 8 to 12 hours. All louse treatments are repeated in 7 to 10 days to kill newly hatched lice.

After a drug application, nits must be removed manually, because drugs do not kill all nits and because it is not possible to distinguish between living and dead nits. Removal requires a fine-tooth comb—which is often packaged with the medication—and careful searching (hence the term "nit-picking"). Because the nits are so strongly stuck to the hair, several nonprescription preparations are available to loosen them. The nits of body lice are destroyed simply by throwing away infested clothing.

Sources of infestation (combs, hats, clothing, and bedding) should be decontaminated by laundering or dry cleaning.

Scabies is a mite infestation that produces tiny reddish bumps and severe itching.

Scabies is caused by the itch mite Sarcoptes scabiei. The infestation spreads easily from person to person on physical contact, often spreading through an entire household. In rare cases, mites can be spread on clothing, bedding, and other shared objects, but their survival is brief, and normal laundering destroys them.

The female itch mite tunnels in the topmost layer of the skin and deposits her eggs in burrows. Young mites (larvae) then hatch in a few days. The infestation causes intense itching, probably from an allergic reaction to the mites.

Symptoms and Diagnosis

The hallmark of scabies is intense itching, which is usually worse at night. The burrows of the mites are often visible as very thin lines up to ½ inch long, sometimes with a tiny bump at one end. Sometimes, only tiny bumps are seen, many of which are scratched open because of the itching. The burrows can be anywhere on the body except the face. Common sites are the webs between the fingers and toes, the wrists, ankles, buttocks, and, in males, the genitals. Over time, the burrows may become difficult to see because they are obscured by inflammation induced by scratching. People with a weakened immune system may develop severe infestations, which produce large areas of thickened, crusted skin.

Usually, itching and the appearance of burrows are all that are needed to make a diagnosis of scabies. However, a doctor can confirm the diagnosis by taking a scraping from the bumps or burrows and looking at it under a microscope to confirm the presence of mites, eggs, or mite feces.


Scabies can be cured by applying a cream containing 5% permethrin, which is left on the skin overnight and then washed off. Although only one treatment is usually needed, some people require a second treatment a week later. Ivermectin taken by mouth in two doses given a week apart also is effective and is especially helpful for severe infestations in people with a weakened immune system.

Even after successful treatment, itching may persist for up to 2 weeks because of a continued allergic reaction to the mite bodies, which remain in the skin for a while. The itching can be treated with mild corticosteroid cream and antihistamines taken by mouth Occasionally, the skin irritation and deep scratches lead to a bacterial infection, which may require antibiotics given by mouth.

Family members and people who have had close physical contact, such as sexual contact, with a person with scabies should be treated as well. Clothing and bedding used during the preceding few days should be washed in hot water and dried in a hot dryer or can be dry cleaned.

Adapted from: Merck & Co. Inc.