Pediculosis is a superficial infestation caused by lice. The three types of lice that contribute to human disease are Pediculus humanus capitis (head louse) (Fig. 90-1), Pediculus humanus corporis (body louse) (Fig. 90-2), and Pthirus pubis (pubic or crab louse) (Fig. 90-3). The head louse is, by far, the most common louse infection seen in children. The prevalence of head lice is about 10% in school children with 6 to 11 year olds the most affected age group.9 Females are preferentially affected which is thought to be due to their longer hair and greater sharing of fomites.9 Contrary to popular belief, head lice can also be found in children with proper hygiene.9,10
Adult female human head louse (Pediculus capitis) on a nit (louse egg) comb.
Pediculosis humanus corporis, the body louse.
Pediculosis Phthirus pubis, the crab louse.
Lice are bloodsucking obligate parasites of humans. They attach their eggs (nits) firmly to hair shafts of their hosts, close to the skin (Fig. 90-4). They are transmitted by direct human contact or the sharing of clothing or other personal articles. Lice require a hair-bearing surface to survive, with the adult viable for only 2 days and the nit for 10 days off of the host. The female may lay up to 300 nits (eggs) which will hatch in 6 to 10 days and assume the adult form 10 days after hatching. Itching is the most common patient complaint but local erythema or papules at the site of infection is sometimes reported.10
Pediculosis capitis: multiple nits on scalp hair. Myriads of nits (oval, grayish-white egg capsules) are firmly attached to the hair shafts, visualized with a lens. On close examination, these have a bottle shape.
The diagnosis of a head lice infestation is made by checking the patient's scalp for nits and live lice. A confirmation of the diagnosis is made only when live lice are found. The scalp may be examined by combing through the hair with a fine toothed comb (louse comb) looking for live lice. Most of the eggs are laid at the nape of the neck or behind the ears, so the clinician should inspect these areas with particular attention. Eggs may remain after the larvae have hatched therefore the detection of nits alone does not confirm an infestation.10
When the diagnosis of head lice is made, a concerted effort to decontaminate the environment is recommended. Furniture needs to be vacuumed and clothing dried at >60°C. Clothing and fomites that cannot be dried should be placed in a bag for at least 3 days and possibly 13 to prevent hatching of nits.9 Boiling of hairbrushes will kill the lice and nits.9 An adjunctive treatment to chemical agents is wet-combing of hair with a fine-toothed comb every 3 to 4 days to remove live lice as they hatch.10 It is recommended that all close the contacts of the affected individual be treated as well to increase cure rates. Permethrin supplied as a 1% cream rinse is a more potent pediculocidal agent than natural pyrethrins and has a residual activity of 2 weeks. Cure rates are increased if reapplied a week after the initial application. It is applied to the scalp on shampooed hair and washed off after 10 minutes. The patient may experience burning, tingling, numbness, and erythema after application. There are reports of increasing resistance to permethrin.11 Recently a new pediculocidal medication spinosad (Natroba) topical suspension 0.9% has been approved by the Federal Drug Administration for the treatment of lice.9 This medication is often effective with one dose and unlike permethrin, parents do not have to comb for nit removal.9 Spinosad can cause benzyl alcohol toxicity and is not recommended for patients younger than 6 months of age.9 Lindane is a topical ovicidal agent that has been encountering resistance and is therefore no longer recommended for treatment in children due to potential neurotoxicity.9 Malathion has been used to treat lice infestations as well but because of its flammability, bad odor, and 8 to 12 hours application time, it is not as popular as other options.11
Typically, no ancillary studies are necessary to diagnose pediculosis.
Sarcoptes scabiei (scabies) are human mites which cause superficial skin infestation. There are an estimated 300 million infected individual worldwide with no predilection for age, gender, or socioeconomic class.10
Scabies are primarily transmitted by direct close and prolonged human contact but can also be spread by fomites. Human scabies may survive for 24 to 36 hours off of a host.9 Although it only takes a mite 30 minutes to create a burrow, patients are often not symptomatic until 4 to 6 weeks after infestation because of a delayed immune response.9,10 Scabies can cause secondary skin infection, sepsis, or even glomerulonephritis.10
Symptoms of scabies infection include pruritis, which is worse at night, infants will often sleep poorly, rubbing their hands and feet together because of the itching. Small red, raised, papules are formed which may progress to vesicles and pustules. Secondary excoriations are also commonly present. There are three forms of scabies—classical, crusted, and nodular. Classical scabies is the most common and reflects a lower mite burden while crusted scabies generally reflects a higher mite burden and is often seen in the immunocompromised and mentally/physically handicapped.9 Classic scabies presents as a rash in the interdigital web spaces, in the genital region, or around the nipples.10 The burrow made by the female mite is the pathognomonic sign of scabies.10 Nodular scabies is the least common and appear as red/brown nodules representing a hypersensitivity reaction to the mites and their byproducts.9 The diagnosis of scabies is made clinically. One may also scrape burrows or papules overlaid with mineral oil and inspect the scraping for adults, eggs, and excreta for confirmation (Fig. 90-5). Of note, scabies in infants and very young children may not be seen in the classic skin areas and instead are seen as vesicles, papules, and pustules in the hands, feet, body folds, the head, and behind the ears.10
Scabies. Microscopic examination of a mineral oil preparation after scraping a burrow reveals a gravid female mite with oval, gray eggs and fecal pellets
A single application of 5% permethrin cream is curative for children older than 2 months. The cream may be applied to the face and scalp and needs to be left for 8 hours. Permethrin has been found to have a 97.8% cure rate with one application.9 Permethrin may cause burning and stinging as well as exacerbation of itching although it is generally very well tolerated and has low potential for toxicity.10 Younger children may be treated with sulfur precipitated in petrolatum.9 The long incubation period makes treating the entire family advisable. Because the parasite lives for only 24 to 36 hours off the host, environmental decontamination may not be necessary; however, it is recommended that fomites be dried at 60°C for 10 minutes and surfaces such as furniture should be vacuumed.9
A clinical diagnosis of scabies should be confirmed by obtaining a skin sample demonstrating the presence of the mite, its eggs, or feces in skin samples. To find the mite, one may either use a scalpel or sterile needle to remove the mite from its burrow or perform skin scrapings. It is preferable to use mineral oil or saline to visualize evidence of a scabies infection. 11
Cimex lecularius is the blood-feeding insect parasite that causes the symptoms associated with bed bugs. The adult is flat and reddish brown and can be visualized without a microscope. Bed bugs have recently emerged as a problem in developed countries in part due to increased travel and insecticide resistance. They rely on the human host for survival.9,12
Bed bugs preferentially feed on the blood of their human hosts at night. They are not known to transmit disease such as HIV and hepatitis. Patients usually present with an allergic reaction to the bites which are usually clustered in small areas of exposed skin. The skin reactions are varied and may appear as anything from macules to indurated bullous lesions.9
A bed bug infestation is usually discovered when a patient presents with pruritis and bug bites with an unknown etiology. Confirmation of an infestation occurs when one sees the insect and/or their fecal specks in the seams of the mattress or box spring. Blood spots may also be found on the mattress.9,12
Treatment of bed bug bites is largely symptomatic with antihistamines and glucocorticoids treating pruritis; however, secondary infections should be treated with systemic oral antibiotics. To eradicate bed bugs, a professional exterminator should be utilized and the environment should be vacuumed and clothing/bedding dried at a high temperature.9,12
No ancillary studies are typically necessary to diagnose bed bug's infections.