Parasitic Skin Infestation
Lice infestation affects people of all ages. Three varieties of lice infest humans: Pediculus humanus capitis (ie, head louse), Pedicu-lus humanus corporis (ie, body louse), and Phthirus pubis (ie, pubiclouse or crab louse). Lice are called ectoparasites because they live on the outside of the host’s body. They depend on the host for their nourishment, feeding on human blood approximately five times each day. They inject their digestive juices and excrement into the skin, which causes severe itching.
Pediculosis capitis is an infestation of the scalp by the head louse. The female louse lays her eggs (ie, nits) close to the scalp. The nits become firmly attached to the hair shafts with a tenacious sub-stance. The young lice hatch in about 10 days and reach matu-rity in 2 weeks.
Head lice are found most commonly along the back of the head and behind the ears. The eggs are visible to the naked eye as sil-very, glistening oval bodies that are difficult to remove from the hair. The bite of the insect causes intense itching, and the resul-tant scratching often leads to secondary bacterial infection, such as impetigo or furunculosis. The infestation is more common in children and people with long hair. Head lice may be transmit-ted directly by physical contact or indirectly by infested combs, brushes, wigs, hats, and bedding.
Treatment involves washing the hair with a shampoo containing lindane (Kwell) or pyrethrin compounds with piperonyl butox-ide (RID or R&C Shampoo). The patient is instructed to sham-poo the scalp and hair according to the product directions. After the hair is rinsed thoroughly, it is combed with a fine-toothed comb dipped in vinegar to remove any remaining nits or nit shells freed from the hair shafts. They are extremely difficult to remove and may have to be picked off one by one with the fingernails.
All articles, clothing, towels, and bedding that may have lice or nits should be washed in hot water—at least 54°C (130°F)— or dry-cleaned to prevent re-infestation. Upholstered furniture, rugs, and floors should be vacuumed frequently. Combs and brushes are also disinfected with the shampoo. All family mem-bers and close contacts are treated. Complications such as severe pruritus, pyoderma, and dermatitis are treated with antipruritics, systemic antibiotics, and topical corticosteroids.
The nurse informs the patient that head lice may infest anyone and are not a sign of uncleanliness. Because the condition spreads rapidly, treatment must be started immediately. School epidemics may be managed by having all of the students shampoo their hair on the same night. Students should be warned not to share combs, brushes, and hats. Each family member should be inspected for head lice daily for at least 2 weeks. The patient should be in-structed that lindane may be toxic to the central nervous system when used improperly.
Pediculosis corporis is an infestation of the body by the body louse. This is a disease of unwashed people or those who live in close quarters and do not change their clothing. Pediculosis pubis is extremely common. The infestation is generally local-ized in the genital region and is transmitted chiefly by sexual contact.
Chiefly involved are those areas of the skin that come in closest contact with the underclothing (ie, neck, trunk, and thighs). The body louse lives primarily in the seams of underwear and cloth-ing, to which it clings as it pierces the skin with its proboscis. Its bites cause characteristic minute hemorrhagic points. Widespread excoriation may appear as a result of intense itching and scratch-ing, especially on the trunk and neck. Among the secondary le-sions produced are parallel linear scratches and a slight degree of eczema. In long-standing cases, the skin may become thick, dry, and scaly, with dark pigmented areas.
Itching is the most common symptom of pediculosis pubis, particularly at night. Reddish brown dust (ie, excretions of the insects) may be found in the patient’s underclothing. The pubic area should be examined with a magnifying glass for lice crawl-ing down a hair shaft or nits cemented to the hair or at the junc-tion with the skin. Infestation by pubic lice may coexist with sexually transmitted diseases such as gonorrhea, herpes, or syphilis. There may also be infestation of the hairs of the chest, armpit, beard, and eyelashes. Gray-blue macules may some-times be seen on the trunk, thighs, and axillae as a result of ei-ther the reaction of the insects’ saliva with bilirubin (converting it to biliverdin) or an excretion produced by the salivary glands of the louse.
The patient is instructed to bathe with soap and water, after which lindane (Kwell) or 5% permethrin (Elimite) is applied to affected areas of the skin and to hairy areas, according to the product directions. An alternative topical therapy is an over-the-counter strength of permethrin (1% Nix). If the eyelashes are in-volved, petrolatum may be thickly applied twice daily for 8 days, followed by mechanical removal of any remaining nits.
Complications, such as severe pruritus, pyoderma, and der-matitis, are treated with antipruritics, systemic antibiotics, and topical corticosteroids. Body lice can transmit epidemic rickettsial disease to humans such as epidemic typhus, relapsing fever, and trench fever. The causative organism may be in the gastrointesti-nal tract of the insect and may be excreted on the skin surface of the infested person.
All family members and sexual contacts must be treated and ed-ucated in personal hygiene and methods to prevent or control in-festation. The patient and partner must also be scheduled for a diagnostic workup for coexisting sexually transmitted disease. All clothing and bedding should be machine washed in hot water or dry-cleaned.
Scabies is an infestation of the skin by the itch mite Sarcoptes sca-biei. The disease may be found in people living in substandardhygienic conditions, but it is also common in very clean individ-uals and among the sexually active, although infestations do not depend on sexual activity. The mites frequently involve the fin-gers, and hand contact may produce infection. In children, overnight stays with friends or the exchange of clothes may be a source of infection. Health care personnel who have prolonged hands-on physical contact with an infected patient may likewise become infected.
The adult female burrows into the superficial layer of the skin and remains there for the rest of her life. With her jaws and the sharp edges of the joints of her forelegs, the mite extends the bur-row, laying two or three eggs daily for up to 2 months. She then dies. The larvae hatch from the eggs in 3 to 4 days and progress through larval and nymphal states to form adult mites in about 10 days.
It takes approximately 4 weeks from the time of contact for the patient’s symptoms to appear. The patient complains of severe itching caused by a delayed type of immunologic reaction to the mite or its fecal pellets. During examination, the patient is asked where the itch is most severe. A magnifying glass and a penlight are held at an oblique angle to the skin while a search is made for the small, raised burrows. The burrows may be multiple, straight or wavy, brown or black, threadlike lesions, most commonly ob-served between the fingers and on the wrists. Other sites are the extensor surfaces of the elbows, the knees, the edges of the feet, the points of the elbows, around the nipples, in the axillary folds, under pendulous breasts, and in or near the groin or gluteal fold, penis, or scrotum. Red, pruritic eruptions usually appear between adjacent skin areas. The burrow, however, is not always visible. Any patient with a rash may have scabies.
One classic sign of scabies is the increased itching that occurs at night, perhaps because the increased warmth of the skin has a stimulating effect on the parasite. Hypersensitivity to the organ-ism and its products of excretion also may contribute to the itch-ing. If the infection has spread, other members of the family and close friends also complain of itching about a month later.
Secondary lesions are quite common and include vesicles, papules, excoriations, and crusts. Bacterial superinfection may re-sult from constant excoriation of the burrows and papules.
The diagnosis is confirmed by recovering S. scabiei or the mites’ byproducts from the skin. A sample of superficial epidermis is scraped off the top of the burrows or papules with a small scalpel blade. The scrapings are placed on a microscope slide and exam-ined through a low-powered microscope to demonstrate the miteat any stage (eg, egg, egg casing, larva, nymph, adult) and fecal pellets.
Elderly patients living in long-term care facilities are more sus-ceptible to outbreaks of scabies because of close living quarters, poor hygiene due to limited physical ability, and the potential for incidental spread of the organisms by nursing staff.
Although the older patient itches severely, the vivid inflam-matory reaction seen in younger people seldom occurs. Scabies may not be recognized in the elderly person; the itching may erroneously be attributed to the dry skin of old age or to anxiety.
Health care personnel in extended-care facilities should wear gloves when providing hands-on care for a patient suspected of having scabies until the diagnosis is confirmed and treatment ac-complished. It is advisable to treat all residents, staff, and fami-lies of patients at the same time to prevent reinfection. Because geriatric patients may be more sensitive to side effects of the scabi-cides, they should be closely observed for reactions.
The patient is instructed to take a warm, soapy bath or shower to remove the scaling debris from the crusts and then to dry thor-oughly and allow the skin to cool. A prescription scabicide, such as lindane (Kwell), crotamiton (Eurax), or 5% permethrin (Elim-ite), is applied thinly to the entire skin from the neck down, spar-ing only the face and scalp (which are not affected in scabies). The medication is left on for 12 to 24 hours, after which the patient is instructed to wash thoroughly. One application may be cura-tive, but it is advisable to repeat the treatment in 1 week.
The patient should wear clean clothing and sleep between freshly laundered bed linens. All bedding and clothing should be washed in hot water and dried on the hot dryer cycle, because the mites can survive up to 36 hours in linens. If bed linens or clothing cannot be washed in hot water, dry-cleaning is advised.
After treatment is completed, the patient should apply an ointment, such as a topical corticosteroid, to skin lesions because the scabicide may irritate the skin. The patient’s hypersensitivity does not cease on destruction of the mites. Itching may continue for several weeks as a manifestation of hypersensitivity, particu-larly in atopic (allergic) people. This is not a sign that the treat-ment has failed. The patient is instructed not to apply more scabicide because it will cause more irritation and increased itch-ing and advised not to take frequent hot showers because they can dry the skin and produce itching. Oral antihistamines such as diphenhydramine (Benadryl) or hydroxyzine (Atarax) can help control the itching.
All family members and close contacts should be treated simul-taneously to eliminate the mites. Some scabicides are approved for use in infants and pregnant women. If scabies is sexually transmitted, the patient may require treatment for coexisting sexu-ally transmitted disease. Scabies may also coexist with pediculosis.
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