Rudolph's Pediatrics, 22nd Ed.

CHAPTER 368. Infestations

Denise W. Metry

SCABIES

Scabies is a common condition in children caused by an infestation of the Sarcoptes scabiei mite. Scabies is primarily contracted by direct contact with an infested person; therefore, the acquisition and spread of scabies, particularly from parents to children, or mother to infant, occurs with relative ease. The highest prevalence is in children younger than 2 years. The disease affects all age groups, races, and social classes; however, poor socioeconomic conditions, in particular, crowding, lack of proper hygiene, and immunosuppression, are risk factors for the disease. The female mite burrows through the skin, leaving behind a trail of debris, eggs, and feces. Clinical findings result from hypersensitivity and irritation to the mite and mite products. Scabies infestation is extremely pruritic and notoriously worse at night. Frequently, other family members also complain of itching.

The distribution of scabies lesions is helpful in making the diagnosis. In infants, the insteps of the feet are commonly affected, often with vesicles or pustules. An important diagnostic clue is an infant who is vigorously rubbing his or her feet together in an attempt to relieve itching. Unlike older children, infants commonly have involvement of the palms and soles, axillae, and scalp. The characteristic distribution of scabies lesions at any age is wrists, finger web spaces, and waistline. Pruritic, nodular lesions of the area around the nipples, umbilicus, axillae, or genitalia are also suspicious for scabies. Lesions in children are generally more inflammatory than in adults and are often vesicular or bullous. A unique clinical feature is the finding of the scabies burrow, which, although difficult to find in children, can be seen as a gray threadlike trail of scale on the skin.

Clinical variants of scabies may present diagnostic difficulties. For example, scabies incognito occurs when treatment with topical or oral glucocorticoids masks the characteristic symptoms and signs of scabies. Lesions may be atypical in both appearance and distribution and are generally more widespread. Crusted (Norwegian) scabies is a highly contagious form of scabies often seen in immunocompromised or debilitated, often institutionalized, patients. Widespread scale and crust formation is present, which may be remarkably thick over the palms, soles, and nails. Nodular scabies presents with discreet, orange-red nodules affecting the axillae and groin. Similar to the tick granuloma, nodules most likely represent a hypersensitivity reaction to retained mite parts or antigens. Lesions may persist for weeks to months and are often resistant to therapy.1

The scabies preparation is a simple and rapid means of establishing the diagnosis of scabies. Using a mineral oil–coated Joseph knife or sterile scalpel blade, multiple lesions are scraped. It is ideal to perform this procedure on the child’s caregiver if he or she has skin findings suspicious for scabies. The best lesions for diagnosis are burrows, vesicles, and unexcoriated papules, and the best scrapings obtain the material underneath the tops and crusts of lesions. The material obtained is then transferred onto a glass slide and examined microscopically under low power. Actively moving mites, eggs, and/or feces can often be found in patients in whom the diagnosis is strongly suspected, but skin scrapings have low sensitivity and should not be used to exclude the diagnosis. Dermoscopy (examination of the skin surface with a dermatoscope) may be a useful tool for diagnosis in situations where equipment for scraping is available and the clinician is trained in its use.2

First-line therapies for scabies in adults and children are permethrin 5% cream or oral ivermectin. Permethrin is reasonably safe even when applied to infants younger than 1 month because less than 2% of the applied amount is absorbed and rapidly detoxified. Permethrin has less potential for neurotoxicity than lindane, particularly in children, in whom lindane should be avoided. Adverse reactions to permethrin most commonly result from sensory irritation and are typically mild and short lived. However, the US preparation of permethrin also contains 0.1% formaldehyde, which is a common cause of allergic contact dermatitis. Permethrin is applied at bedtime and washed off in the morning, after 8 to 14 hours. Patients should massage the cream thoroughly into the skin from the neck to the soles of the feet. In infants, the hairline, temples, and forehead should also be treated. A repeat application is often recommended after 1 week.

The oral antihelmintic ivermectin can also successfully treat scabies. The Centers for Disease Control and Prevention (CDC) recommends ivermectin (200 mcg/kg by mouth as a single dose with a repeat dose 2 weeks later) as an equivalent option to topical permethrin. However, due to greater toxicity risks, the CDC does not recommend its use in pregnant or lactating women. Furthermore, safety has not been determined in children who weigh less than 15 kilograms. It is recommended that patients with crusted scabies be treated simultaneously with both permethrin and ivermectin as directed previously. Topical keratolytics may also be needed for cases with particularly thick areas of crusting.3 To avoid reinfestation, the child and all close contacts must be treated simultaneously. All clothing, bedding, and other items that have been in intimate contact with the child must be simultaneously washed and thoroughly dried, preferably on high heat settings, bagged for several days, or dry cleaned. Under average conditions, mites can survive off a host for 24 to 36 hours, and thus contraction can occur from heavily infested bedding or clothing.1Symptomatic scabies treatment includes oral antihistamines and the application of low-potency hydrocortisone creams.

Papular and pustular skin lesions generally resolve within 1 week following treatment. Nodular lesions may persist for months, and can be treated with intralesional corticosteroid injections or occluded topical steroids. Pruritus may continue for up to 6 weeks secondary to continued hypersensitivity to dead mite parts. This phenomenon must be explained to parents, who often believe that their child has been inadequately treated. The development of new skin lesions more than 2 weeks after initial therapy, however, does suggest either reinfestation or inadequate treatment. The diagnosis of scabies carries significant social implications and requires patience, understanding, and thorough explanation by the treating physician.

LICE

Infestations with head lice are an increasing problem in the United States and other countries; the causative organism is the Pediculus humanus capitis louse. Infestation with head lice can occur at any age and within any socioeconomic group. However, the incidence is most common in female, school-age children and is 35 times higher in Caucasians than African Americans. The latter predilection is believed to be the result of differences in the hair shaft structure, which is oval shaped and may be more difficult for a louse to grasp. Head lice are most commonly spread by direct head-to-head contact or from shared fomites such as brushes, combs, or hats. Adult lice can survive up to 55 hours without a host, but do not jump, fly, or use pets as vectors. Infestation is not related to poor hygiene or hair length.

Lice infestation most commonly manifests as intense scalp itching, particularly at the occipital or retro auricular areas, as a result of sensitization to louse salivary or fecal antigens. Pruritic papules may be seen on adjacent areas of the face and nape of the neck. Other common findings are secondary infection, cervical adenopathy, and fever, although children may manifest no signs or symptoms for 4 to 6 weeks following infestation. Close examination will reveal multiple, oval, grayish-white egg capsules (nits) that are firmly attached to the hair shaft. The louse itself is gray, 2 to 3 millimeters long, and lives on the hair closest to the scalp. Diagnosis is confirmed by plucking the visibly affected hairs, which can then be examined microscopically under low power. Active infestation is based on the finding of adult lice, immature nymphs, and/or viable eggs. Nits are not diagnostic of active infestation because they may persist for months after successful therapy.

Topical insecticides, including permethrin, synthetic pyrethrin, natural pyrethrin, or malathion, are the initial treatment of choice for lice, although emerging resistance is a widely recognized problem. Over-the-counter permethrin 1% cream rinse (Nix) is still considered first-line therapy due to its excellent safety profile. Notably, prescription-strength permethrin (5%) is no more effective than the over-the-counter preparation. Lotions containing pyrethrins and piperonyl butoxide (Rid, A-200, Pronto, Clear), made from a natural chrysanthemum extract, are neurotoxic to lice but have extremely low mammalian toxicity. These products are contraindicated in patients who are allergic to ragweed, chrysanthemums, or other permethrin products. Importantly, cross-resistance among pyrethroids is common; therefore, new pyrethroid preparations will likely add little to existing treatment options.4

The hair is washed with a regular shampoo, rinsed with water, and towel dried. The insecticide is then generously applied, left on for 10 minutes, and rinsed with water (permethrin) or shampoo (pyrethrin). A second application in 10 days is recommended because of current US resistance patterns. Resistance should be suspected if live lice are still present 2 to 3 days after a product has been used correctly and no other cause for treatment failure can be identified.5

Malathion lotion 0.5% (Ovide), available by prescription in the United States, is an alternative topical insecticide that is applied for 8 to 12 hours before washing. Malathion resistance appears to be relatively uncommon in the United States at present, and so is a reasonable alternative to consider in resistant cases.6 It is also considered safe in pregnant or breast-feeding women. Malathion has an unappealing odor, can cause stinging of the skin and eyes, and is flammable.

Although off label, an alternative to topical agents is ivermectin 200 mcg/kg as a single dose by mouth, with a repeat dose 2 weeks later. Ivermectin should be avoided in pregnant or lactating women and children weighing less than 15 kg because adequate safety data in these populations have not been established.7 Resistance to ivermectin has not been reported to date. The benefit of combining oral sulfa with a topical pediculicides is controversial.8,9Veterinary agents, such as fipronil (commonly used as a topical flea preventative) and imidacloprid, show some promise, but human toxicology data are sparse, and therefore, use is not currently recommended in children.10 Piperonal is a pediculicides with excellent repellent action against lice, but data are limited and no commercial preparation is yet available in the United States.11 Physical agents with less potential toxicity (eg, “hot air” devices) are of interest, but evidence suggests that a 30-minute application may be necessary and thus compliance may be poor. Furthermore, although such methods result in high egg mortality, more variable success is seen with killing hatched lice.12

Empty nits may be removed with either 8% formic acid or a 1:1 mixture of vinegar and water, which is applied to the hair for 15 minutes. The nits can then be removed with gentle combing of the hair using a fine-toothed comb. Similar to scabies infestation, all family members should be simultaneously treated, even if asymptomatic. Intimate fomites such as hats, towels, and pillowcases must be washed and dried on hot settings. Clothing that is not washable can be dry cleaned or bagged for several days. Brushes, combs, and other hair items should be washed in hot (130°F), soapy water for 10 to 20 minutes. Alternatively, these items may be pretreated with a pediculicides (alcohol, bleach) for 15 minutes and then washed in hot, soapy water. Floors, play areas, and furniture should be thoroughly vacuumed to remove any shed hairs that may have viable eggs attached.

Community education about the signs of louse infestation and routine screening of schoolchildren by the school nurse are important. “No nit” policies, however, have done little to prevent the spread of lice and exclude many children from the classroom unnecessarily. Children should be allowed to return to school or childcare facilities after the first application of a pediculocide.13

Body lice and pubic lice are responsible for pediculosis corporis and pediculosis pubis, respectively. The pubic louse can be distinguished from the head or body louse by its short body and longer crablike legs. Body lice are a correlate of poor hygiene, whereas pubic lice should be considered a sexually transmitted disease. Natural or synthetic permethrins can be used either as a 10-minute shampoo or as a lotion left on for 8 to 12 hours. Lindane is also effective. Treatment should be repeated in 1 week. Sexual partners of patients with pediculosis pubis should be treated simultaneously.

MITES AND OTHER BITES

 FLEAS

Household pets (cats and dogs) are usually responsible for bringing fleas into households from the immediate outdoors. The itching of flea bites is caused by an allergic reaction. Sensitivity to flea bites varies between people, although children often have especially severe reactions and are more likely to be symptomatic because tolerance to flea bites generally develops with age.

Typical lesions are pruritic papules that may have a tiny central punctum, indicative of the bite itself. Extremely sensitive and/or very young patients may develop bullous lesions. Most commonly, the majority of lesions are present below the knees because fleas are able to jump to a height of only about 18 centimeters. Microscopic evaluation of debris from the suspected pet’s bedding material often confirms the diagnosis. Close examination of the animal may also reveal dried flea feces, crusting, or hair loss, especially over the lower back and base of the tail.

Pruritus should be treated with topical anti-pruritics (eg, calamine lotion) and/or oral antihistamines in order to minimize secondary infection from excessive scratching. Effective flea eradication requires treatment of both the infested animal and its living quarters. Sandy soil and gravel driveways are especially suitable environments for larvae. Spraying the lawn or driveway 20 feet beyond the area frequented by people or pets is recommended. One application of carbaryl, malathion, or rotenone will prevent fleas from being carried into the home. Pets must be treated with an insecticide (most commonly, carbaryl, resmethrin, malathion, pyrethrins, rotenone, or flea collars) from the pet shop or veterinarian. In the home, a vacuum cleaner will help remove fleas, with the bag sealed in a plastic bag before disposing. For light flea infestations, it is often adequate to treat only areas where fleas are most likely to be found. Preferred insecticides are pyrethroids such as resmethrin, allethrin, and tetramethrin, as well as malathion, propoxur, dichlorvos, and rotenone, all of which have some residual effect. Pyrethrins can also be used, but will primarily kill only fleas that are actually sprayed and have little residual effect. For heavy flea infestations, a vacuum should be used to remove lint or dust from cracks or folds in the floor, rugs, and furniture, followed by use of a time-release aerosol insecticide bomb. A treated home should not be reentered for at least 4 hours.14,15

 BEDBUGS

The common bedbug Cimex lectularius and the tropical bedbug Cimex hemipterous are small (ie, 4–5 mm × 3 mm), red-brown, dorsoventrally flattened insects that feed almost exclusively on human blood. They usually hide in cracks and crevices during the day and become active at night, feeding on individuals while they are sleeping. It generally takes 5 to 10 minutes for a bedbug to complete a feeding, after which it retreats to its hiding place (eg, the mattress or behind a piece of loose wallpaper). There often are telltale blood stains on the night clothes overlying the site of the bites or on the bedding, or small reddish-brown specks of dung.

Initially affected, individuals may have few complaints; however, once hypersensitivity develops, the bites can be intensely pruritic. Typically, one can find several linear red urticarial or papular lesions in a row (the “breakfast, lunch, and dinner” sign), usually on exposed areas. At times, bullae may be seen. Bites typically take 3 to 6 weeks to heal; treatment is symptomatic.

The only way to definitively identify a bedbug infestation is to collect a specimen in a plastic pill bottle, zipper top plastic bag, or taped to a piece of white paper and send it to an expert for evaluation and identification. Most states in the United States have an extension office or entomology department at a university that can provide this service; other options include contacting the local health department or pest control service. If human bedbugs are definitively identified, a licensed pest control service should be contacted to inspect the area, design a treatment plan, and apply chemical insecticides as appropriate. Elimination of bedbugs requires trained and knowledgeable professionals. In general, bedbugs are not known to spread pathogens that cause disease in humans.16,17

 MOSQUITOES

The annoyance of mosquitoes is second only to their significance as vectors of disease. Mosquito bites commonly cause local allergic reactions, but may also cause severe systemic reactions in individuals susceptible to the mosquito’s irritating salivary secretions, which the mosquito injects to anticoagulate its blood meal. Mosquitoes are most active during the cooler, shadier times of day and typically infest areas of tall grass, bush, wetlands, and swamps. They are attracted to their victims by sight, temperature, and, most important, smell. In general, they prefer men to women, African Americans to Caucasians, bright to dark clothing, and warm, sweaty skin to cool, dry skin. Mosquitoes also prefer young adults to older adults or children. Carbon dioxide released from the human breath and skin can attract a mosquito from up to 36 miles away.

The best all-purpose insect repellent available against biting insects is deet (N, N-diethyl-3-methylbenzamide, previously called N, N-diethyl-m-toluamide), which is active against biting flies, gnats, chiggers, and ticks, but does not repel stinging insects, such as bees, wasps, or fire ants. The American Academy of Pediatrics recommends concentrations of 30% or less in products intended for use in children, although deet should never be applied to newborns younger than 2 months. A repellent should be applied to all exposed skin except the hands (particularly of small children), the areas near the eyes and mouth, and any broken or irritated skin, and should be sprayed in an open area to avoid inhalation. The duration of efficacy of deet is generally 3 to 8 hours, depending on the concentration, the dose applied, and child’s gender; girls demonstrate less protection, independent of serum estradiol levels. The repellent should be washed off the child with soap and water on returning indoors. Clothing should be sprayed with either deet or permethrin. When applied to clothing, permethrin remains efficacious even after several washings, but should not be applied directly to a child’s skin. Of note, products that combine deet with sunscreen are not recommended because the deet may make the sun protective factor of the sunscreen less effective, thus leading to more frequent application of the sunscreen and potential overexposure to deet.18,19

Repellents made from essential oils found in plants, such as cedar, citronella, eucalyptus, and soybean, are generally much less effective repellents; most give short-term protection only. Of note, the following types of repellents are ineffective: wristbands soaked in chemical repellents, garlic or vitamin B1 taken by mouth, ultrasonic devices that give off sound waves designed to keep insects away, bird or bat houses, or backyard bug zappers, which actually serve to attract insects to your yard.20-23

The application of a topical glucocorticoid will effectively reduce the swelling, redness, and pruritus of a mosquito bite. Corticosteroid use on the face or genitalia should be limited to low-potency preparations. Over-the-counter topical antihistamines and anesthetics are popular among parents but should be discouraged because of the potential for associated allergic contact dermatitis. The prophylactic use of the oral antihistamine cetirizine has proved effective in alleviating both immediate and delayed mosquito bite symptoms.

Infants and children, particularly those with no previous exposure to indigenous mosquitoes (eg, immigrants or visitors), are at risk for severe reactions to mosquito bites. Also at risk are individuals with Epstein-Barr virus-associated natural killer/T lymphoproliferative diseases, who may develop necrotic ulcers at the sites of mosquito bites. Cytotoxic chemotherapy in such patients successfully improves these reactions. In rare cases of severe local reactions, oral corticosteroids are beneficial. Recombinant mosquito salivary allergens with biologic activity are now available at a few centers.24–26

 TICKS

Ticks transmit the organisms that cause Rocky Mountain spotted fever, babesiosis, ehrlichiosis, tularemia, typhus, and Lyme disease, among others, and have been implicated in certain viral encephalitides and hemorrhagic fevers. Most reports of tick bites occur in the spring and summer. Ticks have unique barbed mouthparts called chelicerae, which they use to attach to their victims’ skin. A cementlike salivary gland substance is then secreted, which allows the insect to remain securely on the skin while feeding. Feeding occurs for approximately 7 days, until the tick is satisfactorily engorged with blood. The bite is painless.

Reactions to tick bites may result from hyper-sensitivity, injected toxins, or irritation to salivary gland secretions. The typical skin lesion is a solitary, erythematous papule, with or without an attached tick. In severe cases, local swelling, blistering, bruising, and/or pruritus may develop as well as secondary cellulitis. Although most bites heal in 2 to 3 weeks, a persistent, hypersensitivity-type nodule, or tick granuloma, may remain for months to years.

A neurotoxin injected by the feeding tick can cause reversible tick paralysis, which is more common in children. This is an acute, ascending, lower motor neuron paralysis, which may result in respiratory failure and even death. The tick must be attached at least 4 days for signs of paralysis to appear, and the condition will reverse itself if the tick is promptly removed by using a forceps to apply gentle, slow, reverse traction. Careless removal runs the risk of leaving the chelicerae behind in the skin, which then require surgical excision. In some cases, the insect may be so firmly attached that forceps extraction is unsuccessful. In such instances, it is best to infiltrate the area with local anesthesia and then superficially excise the skin underneath the area of attachment. Persistent tick granulomas may be treated surgically or with a local corticosteroid injection.

The best protection available against tick bites is permethrin, which kills ticks on contact. It is recommended that permethrin repellents only be applied to a child’s clothing because the safety profile of skin application has not been established. This chemical is also effective against mosquitoes, biting flies, chiggers, and scabies mites. A spray form is available, which can safely be used on clothing and outdoor equipment. The combined application of deet to the skin and permethrin to clothing creates a formidable barrier against many of the biting insects.27

 CHIGGER BITES

Chigger bites are due to infestation with the larval form of Trombiculid mites, which are most common to the southern United States. Larvae are encountered in outdoor areas such as grasslands, forests, and around lakes and streams, particularly in more humid environments. The mite tends to migrate to areas constricted by clothing (eg, ankles, waistlines). Chigger bites are initially painless but typically become intensely pruritic after a few hours.

The initial lesion is a small, red macule or papule. A minute red point in the center of the lesion may indicate the location of the chigger itself. By 24 hours, the lesion evolves into an intensely pruritic, urticarial papule that is surmounted with a tiny vesicle containing clear fluid. Depending on the site, the lesion can become purpuric or hemorrhagic. Symptoms resolve over a few days, and lesions resolve over 1 to several weeks. Secondary bacterial infection is a common consequence of excoriation. In boys, the triad of penile swelling, pruritus, and dysuria has been referred to as “summer penile syndrome” and likely represents a local hypersensitivity reaction to chigger bites.28

Vigorous cleansing of the skin with soap and water may be helpful in removing the mites. Clothing should also be washed in hot water to kill mites. Symptomatic treatment of pruritus includes topical antipruritics such as menthol or topical corticosteroids, or oral antihistamines. Deet is the most effective repellent against chigger mites, and is best applied to both skin and clothing.29 Pant legs can be tucked inside socks, or knee-high socks can be worn to minimize accessibility of skin to the mites.

 PARASITES (TUNGIASIS, MYIASIS)

Tungiasis and myiasis are common ectoparasitic infestations that occur in tropical developing countries, particularly where poverty and poor standards of basic hygiene exist. Presentation in nonendemic countries usually occurs from international travel to and from these regions. Although these infestations are usually self-limited and present few complications, secondary infections and complications can occur.

 CUTANEOUS MYIASIS

Cutaneous myiasis is an infestation of the skin by developing larvae (maggots) of a variety of fly species within the arthropod order Diptera, the two-winged true fly. The two main clinical types are wound and furuncular (or follicular) myiasis. The most common flies worldwide causing human infestation are Dermatobia hominis (human botfly) and Cordylobia anthropophaga (tumba fly). The route of transmission of fly larvae to human hosts differs among the various fly species. D hominis lays her eggs on mosquitoes, which in turn deposit them on a warm-blooded mammal. C anthropophaga deposits her eggs on moist clothing, soiled blankets, or sand, and can live up to 2 weeks without feeding before making contact with and penetrating a host, initiating further maturation. In wound myiasis, any open wound or orifice may attract flies to deposit their eggs in the vicinity. More serious infestations occur when the scalp, nasal cavity, or sinuses are involved.

Furuncular cutaneous myiasis, caused by the botfly and tumbu fly, results in boillike lesions. Botfly lesions are most common on exposed areas of the body (scalp, face, extremities), whereas lesions from the tumbu fly more commonly occur on the trunk, buttocks, or thighs. An initial pruritic papule at the site of penetration slowly enlarges to a tender nodule that may develop a central necrotic center, crust, and/or purulence. Not uncommonly, the child may relate a sensation of movement. Cochliomyia hominivorax (screw-worm) is the most common cause of wound myiasis in the Americas, whereas Chrysomyia bezziana is most common to Africa, Asia, and Australia. Larvae may be visible on the wound surface or burrow below. Creeping (migratory) cutaneous myiasis resembles cutaneous larva migrans and may be obtained by working with infested horses (Gasterophilus intestinalis) or cattle (Hypoderma bovis).

Myiasis is a self-limiting infestation, typically without serious sequelae, although treatment is often sought to improve pain and cosmesis, or provide psychologic relief. A number of treatment modalities are employed in the management of cutaneous myiasis. Forcible removal of the larva through the punctum is not advised because the larva contains rows of spines and hooks that prevent any simple extraction. Popular methods include suffocation/occlusion of the central punctum, or efforts to “coax” the larva to the surface with the application of bacon to the surface or injection of lidocaine to the base of the nodule. Wound myiasis requires surgical debridement/irrigation or removal. Oral ivermectin, which alters larval development, is an alternative treatment option for all types of myiasis.30

 TUNGIASIS

Tungiasis is caused by the chigoe or sand flea Tunga penetrans and occurs throughout warm, dry soils of the coastal and southern United States, Central and South America, and tropical West and East Africa. Because the fleas possess poor jumping ability, the most common location for bites is the feet. The adult impregnated female burrows into the upper dermis with the posterior tip of the abdomen facing out to breathe, via a central punctum that is seen as a small black dot. This initial burrow is usually asymptomatic. After 2 to 3 weeks, the female has grown to approximately 1 centimeter in diameter, manifesting as a tender nodule. She then begins discharging more than 100 eggs through the central punctum, after which she dies and is sloughed in approximately 20 days, often leaving a small ulcerated site. Tungiasis usually occurs on the lower parts of the lower extremities, especially between the toes and under the toenails, and is painful. Individuals who are barefoot or wear sandals are especially vulnerable, although almost any site can be infected. The condition is self-limited, and the majority resolves without sequelae, although ulceration, secondary infection, lymphangitis, tetanus, gangrene, and amputation of a digit have all been reported. Early removal of the flea can often be done with a sterile needle; in more advanced cases, surgical curettage or excision may be needed. Systemic thiabendazole can be given for severe infestation. Tetanus prophylaxis should also be considered. Tungiasis can be prevented by wearing shoes and by using insect repellents such as deet.30