Eradication of ectoparasites in children

How to treat infestations of lice, scabies, and chiggers

Jerome Potts, MD

VOL 110 / NO 1 / JULY 2001 / POSTGRADUATE MEDICINE

CME learning objectives

• To be able to identify infestations of head lice, body lice, scabies, and chiggers
• To understand the differences between head lice and body lice, their potential for disease, and methods of controlling their spread
• To review methods for preventing and controlling ectoparasite infestations

The author discloses no financial interest in this article.

This is the second of four articles on critters and kids.

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Preview: Infestations of head lice, body lice, scabies, and chiggers are common causes of rash and pruritus in children. Concern has arisen about development of resistance to often-used treatments, but a comprehensive approach to eradication is usually very effective. In this article, Dr Potts describes the presentation of ectoparasites and discusses conservative treatment and the safe use of pediculicides.
Potts J. Eradication of ectoparasites in children: how to treat infestations of lice, scabies, and chiggers. Postgrad Med 2001;110(1):57-64

 Recently, much discussion has centered on an apparent increase in resistance to commonly used remedies for ectoparasite infestations. Although some resistance has been documented, careful use and dosing of medications, fomite treatment, and follow-up care can eradicate most infestations (1).

Laws will take effect in California in 2002 that prohibit the use of shampoo and lotion containing the pediculicide lindane (G-well) because of neurotoxicity in some very young patients (2). Similar legislative action is pending in other states. The US Food and Drug Administration (FDA) has been petitioned to ban the use of lindane nationally but has not taken action.

Head lice

The head louse (Pediculus humanus capitis), which is responsible for the most common pediatric ectoparasite infestation, easily spreads from person to person. Many treatments have been promoted, but most either have not been thoroughly studied or have proved ineffective. Examples of questionable treatments include application to the scalp of tea tree oil (which may contain neurotoxic ingredients), mayonnaise (which has not been sufficiently studied), and petrolatum (which is difficult to remove) (3).

Epidemiologic factors
The head louse is a blood-sucking insect (figure 1: not shown). The female louse lays 7 to 10 eggs daily in egg casings (nits) that are cemented to the base of hair shafts. Newly formed nits are brown; the eggs, which hatch in 8 to 10 days, are white. Nymphs emerge from the egg, mature in 8 to 15 days, and live 9 to 30 days as adults. Both nits and adult lice can survive separated from their blood source for up to 2 weeks.

The head louse is not a vector of human disease. It is exclusively a human parasite, and no environmental reservoir or nonhuman hosts have been identified. Head lice are transmitted by hair-to-hair contact and through fomites (eg, hats, hair accessories). Parents often fear that head lice infestation reflects poor personal hygiene, but hygiene does not have a role. Healthy children between the ages of 3 and 10 years are most commonly affected. Head lice are rare in African American children, probably at least partially because of differences in hair shaft properties.

Clinical features
Scalp pruritus is the most common presentation. Physical examination reveals excoriations and nits at the proximal ends of hair shafts (figure 2: not shown). Because the nits are laid at the base of hair shafts, the height of the nits above the scalp due to hair growth indicates how long the infestation has been present. Posterior cervical adenopathy is also commonly seen. The identification of nits, especially in warmer parts of the scalp (ie, the retroauricular area and base), confirms the diagnosis. Differential diagnostic considerations include conditions that may cause scalp pruritus and hair findings that mimic nits (eg, irritation from use of hairstyling products, scalp disorders). Nodules on the hair shaft that resemble nits may be caused by fungal infections and certain hair shaft abnormalities (eg, monilethrix, trichorrhexis nodosa). However, these abnormalities encompass the hair shaft completely, while nits hang on only one side. Examination of hair shafts under Wood's light can help distinguish dandruff (which has a bright blue-white appearance) from nits (which have a yellow-green appearance).

Treatment
Recent studies suggest that manual removal of nits and lice with a quality nit comb is the mainstay of care (4). Nit removal can be difficult; application of cooking oil to ease combing or of distilled white vinegar to soften the nit attachment is recommended. Shaving the head is not indicated. Treatment may also involve use of pediculicides (table 1); because no preparations are completely ovicidal, reapplication in 1 week is necessary to eradicate newly emerging lice. Washing fomites in hot, soapy water or placing them in a sealed container for 2 to 3 weeks can eliminate nits and live adult lice. In addition, patient and family education is an important aspect of treatment.

Table 1. Some common pediculicides for eradication of lice and scabies in adults and children
Active ingredient	Examples
Crotamiton 10%	Eurax
Lindane 1%*	G-well
Malathion 0.5%*	Ovide
Permethrin 1%	Nix
Permethrin 5%	Acticin, Elimite
Piperonyl butoxide 4% or pyrethrum extract 0.33%	Several over-the-counter shampoos
*Not for use in children under 2 years of age; caution needed when using in children under 6 years.

A tolerance to the standard formulation of permethrin 1% creme rinse (Nix) generally can be overcome through careful use of a permethrin 5% cream (Acticin, Elimite). Simultaneous treatment of close contacts (eg, children living in the same household, those who share clothes or hats) is recommended. Other pediculicide therapies include malathion 0.5% lotion (Ovide) and crotamiton 10% lotion or cream (Eurax). Oral ivermectin (Stromectol), an antihelmintic agent used to treat various parasites, and oral trimethoprim-sulfamethoxazole (Bactrim, Cotrim, Septra) also have been studied (5). Treatment with pediculicides should be avoided in persons with allergies, asthma, epilepsy, open wounds, or preexisting medical conditions. Children who have received more than one treatment for head lice or scabies or who have been exposed to lice sprays or flea bombs may be at increased risk for neurologic side effects, including seizures. More information on complications of use of pediculicides in children can be found at the National Pediculosis Association Web site, http://www.headlice.org.

Body lice

The body louse (Pediculus humanus corporis) looks similar to but is larger than the head louse. The female louse can lay up to 150 eggs a day during her 20-day adult life span. Eggs hatch in 7 to 10 days, and the larvae mature into adults in 9 days.

Epidemiologic factors
Unlike the head louse, the body louse does not live on the skin but, instead, lives and lays eggs in the seams of clothing. The adult louse emerges from clothing to take a blood meal, usually at night. It is also a vector of a variety of human diseases, including typhus, relapsing fever, and trench fever. Body lice are transmitted through use of infested clothing and linens and primarily affect the underprivileged (vagabonds' disease). Poor hygiene plays a major role in transmission of body lice; the best way to control outbreaks is by changing and laundering clothes and linens.

Clinical features
Pruritus with nocturnal exacerbation is the most common symptom of body lice. Examination may show small erythematous papules (bite sites) on covered areas (eg, trunk, axillae, groin). Generally, the face, forearms, and feet are spared. Pyodermas may develop following bacterial infection. Diagnosis rarely is made by identification of live lice on skin. Lice and eggs are most often found by examination of clothing seams (eg, in areas that cover the waist or axillae). Maculae ceruleae, the hemosiderin-stained purpuric spots where lice have fed, suggest a body lice infestation (5). Differential diagnostic considerations include impetigo, acne, folliculitis, bites from other insects, scabies, molluscum contagiosum, and xerosis with subsequent excoriations (6).

Treatment
For isolated infestations, simple hygiene measures (eg, bathing, washing of infested clothing and linens) are adequate. Use of pediculicides such as lindane or permethrin may be useful to augment hygiene measures in epidemic cases.

Scabies

The adult female scabies mite (Sarcoptes scabiei var hominis) is about 0.4 mm long (figure 3: not shown). It burrows into the stratum corneum layer of the skin and lays 2 or 3 eggs a day. The eggs hatch in 3 to 4 days, and the larvae rise to the skin surface and mature in 14 to 17 days. Adult females have a life span of 30 days; the male, which is smaller than the female, dies shortly after mating.

Epidemiologic factors
The highest prevalence of infestations is in children under 2 years of age. Scabies is more prevalent during times of war, in poor or crowded living conditions, and in institutionalized people. The mite is transmitted by close personal contact, including sexual contact. Some researchers believe that the mite may live for up to 3 days on furniture and tiled floors (6).

Clinical features
Pruritus is a common symptom of scabies, when the human host becomes sensitized to the mite. Burrows and erythematous papules typically are noted. Burrows usually appear on the hands, wrists, and genitalia but also may be seen on the axillae, umbilicus, buttocks, and nipples. Erythematous papules typically are seen on the trunk and likely represent an immune response. Excoriations may change the appearance of the lesions, and pustules may develop as a result of infection; this may lead to an inaccurate diagnosis of eczema or another skin problem.

Scabies should be suspected in all patients with a pruritic rash, especially those with nightly worsening. The diagnosis is strengthened if household members have similar signs and symptoms. Erythematous papules on the genitalia or breasts are nearly pathognomonic. Diagnosis can be confirmed on microscopic examination of scrapings from burrows and papules. Mineral oil is placed on a No. 15 scalpel blade, and scrapings from several skin lesions are transferred to a slide, where mite eggs or fecal pellets (scybala) may be seen. However, this technique is often not definitive, even when performed by a physician experienced in it. A trial of antiscabietic therapy after negative results also may confirm the diagnosis (6). Differential diagnostic considerations include atopic and contact dermatitis and lichen planus, which present with similar pruritic papules. Dermatitis herpetiformis or bullous pemphigoid is suggested by bullous or vesicular lesions.

Treatment
Scabies treatment generally involves application of a pediculicide (eg, crotamiton, lindane, permethrin). These agents are washed off several hours after application. Lindane 1% lotion has been the treatment of choice. It should be applied from the neck to the toes at bedtime and washed off 12 to 24 hours later. To avoid increased cutaneous absorption, it should not be applied to wet skin or after bathing. A second application 1 week later is recommended because lindane is not ovicidal, and newly hatched mites may appear after the first treatment. Lindane should not be used in children under 2 years of age, in patients who have undergone multiple scabies treatments, or in those who have asthma, significant coexisting medical problems, or allergies (especially to chrysanthemums, from which lindane is derived).

Permethrin 1% or 5% probably can be safely used in patients as young as 2 months. Like lindane, it should be applied at bedtime and washed off in the morning, and an additional treatment should be completed 1 week later. All household contacts should be treated at the same time. In addition, fomites such as clothing and linens should be washed in soap and hot water, dry-cleaned, or placed in a closed container for 5 to 7 days (7).

Although not approved by the FDA for oral use, orally administered ivermectin has been shown to be safe and effective. One study (6) revealed that a single dose of ivermectin (200 micrograms/kg) is more effective than lindane. Mild and transient adverse effects included headache, hypotension, abdominal pain, and vomiting. No laboratory abnormalities were noted.

Chiggers

Eutrombicula alfreddugesi is the most common cause of chigger infestation in the United States. The adult mite is not a human parasite like the larval form, which hatches from eggs after 1 to 2 weeks and is known as a chigger, red bug, or harvest mite. The adult female lays 40 eggs a month in the soil. The larval form of the mite lives in the grass, soil, and weeds and requires a meal from a vertebrate host to mature.

Epidemiologic factors
The chigger does not feed on blood. Rather, it crawls onto the human host, anchors itself to the skin, injects proteolytic enzymes, and ingests the degraded tissue. The chigger may remain attached to the host for 3 to 4 days, then drops off into the soil to complete its maturation.

Clinical features
Outdoor exposure is a hallmark feature. The bite of a chigger is painless but produces a 2- to 3-mm pale macule. Early on, the larva may still be attached, appearing as a 1-mm red dot in the center of a macule. Over time, the lesions enlarge and become erythematous and pruritic. Lesions typically are found on the ankles and lower extremities but also appear on moist areas of the body (eg, axillae, genitalia, popliteal and antecubital fossae). Pruritus starts within a few hours of a bite and ceases in a few days. Lesions heal in 1 to 2 weeks, although infections of the excoriated lesions are common. In the Far East, the mite is a vector of Rickettsia tsutsugamushi, the infectious agent of scrub typhus (also known as tsutsugamushi fever) (8).

Treatment
Treatment is aimed at relief of pruritus. Prevention primarily involves avoiding areas where the mite is known to live, wearing protective clothing, and using insect repellents, such as 5% to 15% concentrations of DEET (6). However, DEET should not be applied to the hands of small children, who often put their hands into their mouth.

Conclusion

Head lice infestations are easily diagnosed and can almost always be treated conservatively without resorting to pediculicide agents. Body lice can best be controlled by good personal hygiene and the washing of clothes and bed linens. Scabies can be difficult to diagnose because examination of lesion scrapings is often inconclusive. A trial of an antiscabies agent may help with the diagnosis. Chiggers are a common cause of a pruritic rash in persons that spend significant time outdoors.

References

1. Drugs for head lice. Med Lett Drugs Ther 1997;39:6-7
2. Calif Safety Code section 111246
3. Downs AM, Stafford KA, Coles GC. Monoterpenoids and tetralin as pediculocides. Acta Derm Venereol 2000;80(1):69-70
4. De Maeseneer J, Blokland I, Willems S, et al. Wet combing versus traditional scalp inspection to detect head lice in schoolchildren: observational study. BMJ 2000;321(7270):1187-8
5. Elston DM. What's eating you? Pediculus humanus (head louse and body louse). Cutis 1999;63(5):259-64
6. Angel TA, Nigro J, Levy ML. Infestations in the pediatric patient. Pediatr Clin North Am 2000;47(4):921-35
7. Mazurek CM, Lee NP. How to manage head lice. West J Med 2000;172(5):342-5
8. Blankenship ML. Mite dermatitis other than scabies. Dermatol Clin 1990;8(2):265

Dr Potts is assistant chief and medical director, department of family practice, Hennepin County Medical Center, Minneapolis. Correspondence: Jerome Potts, MD, Hennepin County Medical Center, 5 W Lake St, Minneapolis, MN 55408.