Section G: Infestations

PATIENT STORY

A 64-year-old homeless woman with schizophrenia presented to a homeless clinic for itching all over her body. She stated that she could see creatures feed on her and move in and out of her skin. The physical examination revealed that she was unwashed and had multiple excoriations over her body (Figure 148-1). Body lice and their progeny were visible along the seams of her pants (Figure 148-2). Treatment of this lousy infestation required giving her new clothes and a shower.¹

INTRODUCTION

Lice are ectoparasites that live on or near the body. They will die of starvation within 10 days of removal from their human host. Lice have coexisted with humans for at least 10,000 years.² Lice are ubiquitous and remain a major problem throughout the world.³

SYNONYMS

Pediculosis, crabs (pubic lice).

EPIDEMIOLOGY

• Human lice (pediculosis corporis, pediculosis pubis, and pediculosis capitis) are found in all countries and climates.³

• Head lice are most common among school-age children. Each year, approximately 6 to 12 million children, ages 3 to 12 years, are infested.⁴

• Head lice infestation is seen across all socioeconomic groups and is not a sign of poor hygiene.⁵

• In the United States, black children are affected less often as a result of their oval-shaped hair shafts that are difficult for lice to grasp.⁴

• Body lice infest the seams of clothing (see Figure 148-2) and bed linen. Infestations are associated with poor hygiene and conditions of crowding.

• Pubic lice are most common in sexually active adolescents and adults. Young children with pubic lice typically have infestations of the eyelashes. Although infestations in this age group may be an indication of sexual abuse, children generally acquire the crab lice from their parents.⁶

ETIOLOGY AND PATHOPHYSIOLOGY

• Lice are parasites that have six legs with terminal claws that enable them to attach to hair and clothing. There are three types of lice responsible for human infestation. All three kinds of lice must feed daily on human blood and can only survive 1 to 2 days away from the host. The three types of lice are as follows:

  • Head lice (Pediculus humanus capitis)—Measure 2 to 4 mm in length and are uniquely adapted to living on human hair (Figure 148-3).

  • Body lice (Pediculus humanus corporis)—Body lice similarly measure 2 to 4 mm in length and live on clothing between feeding on the human body (Figure 148-4).

  • Pubic or crab lice (Phthirus pubis)—Pubic lice are shorter, with a broader body, and have an average length of 1 to 2 mm (Figure 148-5).

• Female lice have a lifespan of approximately 30 days and can lay approximately 10 eggs (nits) a day.⁴

• Nits are firmly attached to the hair shaft or clothing seams by a gluelike substance produced by the louse (Figures 148-6, 148-7, 148-8).

• Nits are incubated by the host's body heat.

• The incubation period from laying eggs to hatching of the first nymph is 7 to 14 days.

• Mature adult lice capable of reproducing appear 2 to 3 weeks later.⁵

• Transmission of head lice occurs through direct contact with the hair of infested individuals. The role of fomites (e.g., hats, combs, brushes) in transmission is negligible.⁶ Head lice do not serve as vectors for transmission of disease among humans.

• Transmission of body lice occurs through direct human contact or contact with infested material. Unlike head lice, body lice are well-recognized vectors for transmission of the pathogens responsible for epidemic typhus, trench fever, and relapsing fever.⁵

• Pubic or crab lice are transmitted primarily through sexual contact. In addition to pubic hair (Figure 148-9), infestations of eyelashes, eyebrows, beard, and upper-thigh, abdominal, and axillary hairs may also occur.

RISK FACTORS

• Contact with an infected individual.

• Living in crowded quarters such as homeless shelters (Figure 148-10).

• Poor hygiene and mental illness.

DIAGNOSIS

CLINICAL FEATURES

• Nits can be seen in active disease or treated disease. Nits closer to the base of the hairs are generally newer and more likely to be live and unhatched. Unfortunately, nits that were not killed by pediculicides can hatch and start the infestation cycle over again. Note that nits are glued to the hairs and are hard to remove, whereas flakes of dandruff can be easily brushed off.

• Pruritus is the hallmark of lice infestation. It is the result of an allergic response to louse saliva.⁷ Head lice are associated with excoriated lesions that appear on the scalp, ears, neck, and back.

• Occipital and cervical adenopathy may develop, especially when lesions become super-infected.

• Body lice result in small maculopapular eruptions that are predominantly found on the trunk (see Figure 148-1) and the clothing (see Figure 148-2). Also, the pruritus leads to excoriations (Figure 148-10).

• Chronic infestations often result in hyperpigmented, lichenified plaques known as "vagabond's skin."⁸

• Pubic lice produce bluish-gray spots (macula cerulea) that can be found on the chest, abdomen, and thighs.⁸

TYPICAL DISTRIBUTION

• Head lice—Look for nits and lice in the hair, especially above the ears, behind the ears, and at the nape of the neck. There are many more nits present than live adults. Finding nits without an adult louse does not mean that the infestation has resolved (see Figures 148-6 and 148-7). Systematically combing wet or dry hair with a fine-toothed nit comb (teeth of comb are 0.2 mm apart) better detects active louse infestation than visual inspection of the hair and scalp alone.⁹

• Body lice—Look for the lice and larvae in the seams of the clothing (see Figures 148-2 and 148-4).

• Pubic lice—Look for nits and lice on the pubic hairs (see Figure 148-9). These lice and their nits may also be seen on the hairs of the upper thighs, abdomen, axilla, beard, eyebrows, and eyelashes. Little specks of dried blood may be seen in the underwear as a clue to the infestation.

LABORATORY TESTING

• Direct visualization and identification of live lice or nits are sufficient to make a diagnosis (see Figures 148-2, 148-3, 148-4, 148-5, 148-6, 148-7 and 148-9).

• The use of a magnification lens or dermatoscope may aid in the detection or confirmation of lice infestation (see Figure 148-9).

• Under Wood light, the head lice nits fluoresce a pale blue.

• If you find an adult louse, put it on a slide with a coverslip loosely above it. Look at it under the microscope on the lowest power (see Figure 148-5). You will see the internal workings of the live organs. If the louse was not found in a typical location, you can use the morphology of the body and legs to determine the type of louse causing the infestation.

• In cases of pubic lice infestations, individuals should be screened for other sexually transmitted diseases.⁵

DIFFERENTIAL DIAGNOSIS

• Dandruff, hair casts, and debris should be ruled out in cases of suspected lice infestations. Unlike nits, these particles are easily removed from the hair shaft. In addition, adult lice are absent.

• Scabies is also characterized by intense pruritus and papular eruptions. Unlike lice infestations, scabies may be associated with vesicles, and the presence of burrows is pathognomonic. Diagnosis is confirmed by microscopic examination of the scrapings from lesions for the presence of mites or eggs (see Chapter 149, Scabies).

MANAGEMENT

NONPHARMACOLOGIC

FIRST LINE

• In young children or others who wish to avoid topical pediculicides for head lice, mechanical removal of lice by wet combing is an alternative therapy. A 1:1 vinegar:water rinse (left under a conditioning cap or towel for 15 to 20 minutes) or 8% formic acid crème rinse may enhance removal of tenacious nits.⁸ Combing is performed until no lice are found for 2 weeks. SORⒷ

  • Nits are also removed with a fine-toothed comb following the application of all treatments. This step is critical in achieving resolution.

  • Combs and hairbrushes should be discarded, soaked in hot water (at a temperature of at least 55°C [130°F]) for 5 minutes, or treated with pediculicides.¹⁰

SECOND LINE

• The natural substances of tea tree oil and nerolidol were shown in 2012 to have promising results as a natural alternative to pediculosis resistant cases. In the study, a compound ratio of 1:2 (tree oil 0.5% plus nerolidol 1.0%) when applied to head lice and their eggs resulted in 100% death of all head lice after 30 minutes and an ovicidal effect on louse eggs after 5 days.¹¹ SORⒷ

MEDICATIONS

Pediculus humanus capitis (head lice):

FIRST LINE

• Nonprescription 1% permethrin cream rinse (Nix), pyrethrins with piperonyl butoxide (which inhibits pyrethrin catabolism; RID) shampoo, or permethrin 1% is applied to the hair and scalp and left on for 10 minutes, then rinsed out.¹²

• Pyrethrins are only pediculicidal, whereas permethrin is both pediculicidal and ovicidal. It is important to note that treatment failure is common with these agents owing to the emergence of resistant strains of lice. After 7 to 10 days, repeating the application is optional when permethrin is used, but is a necessity for pyrethrin. Lice persisting after treatment with a pyrethroid may be an indication of resistance.¹³ SORⒶ

• Malathion 0.5% (Ovide) is available by prescription only and is a highly effective pediculicidal and ovicidal agent for resistant lice. Malathion may have greater efficacy than pyrethrins.¹⁴ It is approved for use in children age 6 years and older. The lotion is applied to dry hair for 8 to 12 hours and then washed. Repeat application is recommended after 7 to 10 days if live lice are still present. When used appropriately, malathion is 78% to 95% effective.¹⁴ SORⒶ

• Hair conditioners should not be used prior to the application of pediculicides; these products may result in reduced efficacy.¹⁵

• A Cochrane review found no evidence that any one pediculicide was better than another; permethrin, synergized pyrethrin, and malathion were all effective in the treatment of head lice.¹⁶ SORⒶ

SECOND LINE

• Benzyl alcohol 5% lotion (Ulesfia) is a newer treatment option in patients 6 months of age and older. It works by asphyxiating the parasite. It is applied for 10 minutes with saturation of the scalp and hair, and then rinsed off with water. The treatment is repeated after 7 days.¹⁷ SORⒶ

• Spinosad (Natroba) is a topical prescription medication approved by the U.S. Food and Drug Administration (FDA) in 2011 for the treatment of lice. Spinosad is a fermentation product of the soil bacterium Saccharopolyspora spinosa that compromises the central nervous system of lice. It is approximately 85% effective in lice eradication, usually after one application. It is applied to completely cover the dry scalp and hair, and rinsed off after 10 minutes. Treatment should be repeated if live lice remain 7 days after the initial application.¹⁸ SORⒶ

• In February 2012, the FDA approved ivermectin 0.5% lotion for the treatment of head lice. It is applied as a single 10-minute topical application. The safety of ivermectin in infants younger than age 6 months has not been established. SORⒶ

• Permethrin 5% is conventionally used to treat scabies; however, it is anecdotally recommended for treatment of recalcitrant head lice.⁵ SORⒸ

• Oral therapy options include a 10-day course of trimethoprim-sulfamethoxazole or 2 doses of ivermectin (200 mcg/kg) 7 to 10 days apart. SORⒸ Trimethoprim-sulfamethoxazole is postulated to kill the symbiotic bacteria in the gut of the louse.⁴ Combination therapy with 1% permethrin and trimethoprim-sulfamethoxazole is recommended in cases of multiple treatment failure or suspected cases of resistance to therapy.^5,10 SORⒸ

• Abametapir is a new therapy that, in two randomized, double-blind, phase 3 clinical trials published in 2016, was shown to effectively kill both lice and their eggs with one application. Abametapir works by inhibiting metalloproteinases, which are enzymes that are necessary for both egg development and the survival of living lice. The compound comes in a lotion and is applied to dry hair and left to sit for 10 minutes. It is subsequently washed out with warm water and requires no further treatments.¹⁹ Abametapir has yet to be approved by the FDA at the time of writing, but an application is pending.

Pediculus humanus corporis (body lice):

• Improving hygiene and laundering clothing and bed linen at temperatures of 65°C (149°F) for 15 to 30 minutes will eliminate body lice.⁸

• In settings where individuals cannot change clothing (e.g., those who are homeless), a monthly application of 10% lindane powder can be used to dust the lining of all clothing.⁸

• Additionally, lindane lotion or permethrin cream may be applied to the body for 8 to 12 hours to eradicate body lice.

Phthirus pubis (pubic lice):

• Pubic lice infestations are treated with a 10-minute application of the same topical pediculicides used to treat head lice.

• Retreatment is recommended 7 to 10 days later.

• Petroleum ointment applied 2 to 4 times a day for 8 to 10 days will eradicate eyelash infestations.

• Clothing, towels, and bed linen should also be laundered to eliminate nit-bearing hairs.⁸

PREVENTION

• Washing clothing and linen used by the head or pubic lice-infested person during the 2 days prior to therapy in hot water and/or drying the items on a high-heat dryer cycle (54.5°C [130°F]). Items that cannot be washed may be dry cleaned or stored in a sealed plastic bag for 2 weeks.

FOLLOW-UP

• Patients should be reexamined upon completion of therapy to confirm eradication of lice.

PATIENT EDUCATION

• Patients should be instructed to wash potentially contaminated articles of clothing, bed linen, combs, brushes, and hats.

• Nit removal is important in preventing continued infestation as a result of new progeny. Careful examination of close contacts, with appropriate treatment for infested individuals, is important in avoiding recurrence.

• In cases of pubic lice, all sexual contacts should be treated.

REFERENCES

PATIENT STORY

A 17-year-old young man is seen with severe itching of his hands and feet. He has no lesions between his fingers and no one else in the family is itching. He has seen multiple clinicians in the past 5 months and has been given many types of topical steroids and antihistamines. The last clinician referred him for psychotherapy, thinking that this must be psychogenic. On close examination, there are multiple burrows on the hands (Figure 149-1). Dermatoscopy shows the typical pattern of a "jet plane with a contrail," clinching the diagnosis of scabies (Figure 149-2). The patient is treated with permethrin cream overnight and repeated in 7 days. At the following visit his itching is gone, and he is so thankful. This case demonstrates the importance of looking for burrows as the morphologic manifestation of the mite under the skin. Although it was nice to have a dermatoscope to confirm the diagnosis, this diagnosis could easily have been made clinically just by careful observation. Not every patient with scabies has lesions between the fingers and contacts at home with pruritus.

INTRODUCTION

Scabies may be one of the most overdiagnosed and underdiagnosed conditions in medicine. Not every patient with a pruritic rash has scabies, and the patterns of scabies are multiple and variable. Scabies may present with papules, pustules, nodules, and/or crusts, and while there are typical patterns of distribution, each case does not read the textbook (not even this textbook). Looking for burrows is always worthwhile, as it is the pathognomonic feature of scabies. Although there may be nodules in the axilla or on the penis, there probably will be some burrows somewhere, such as on the wrist or between the first and second interspace of the hand. Having a dermatoscope to see the real mite is a great advance in the diagnosis of this potentially elusive condition (see Figure 149-2).

SYNONYMS

Crusted scabies has been called Norwegian scabies. The preferred term is now crusted scabies.

EPIDEMIOLOGY

• Three hundred million cases per year are estimated worldwide.¹ In some tropical countries, scabies is endemic.

• The incidence of scabies in a study performed in general practices in England and Wales was 351 per 100,000 person-years in men and 437 per 100,000 person-years in women.²

• Data from the Royal Infirmary in Edinburgh show that 5% of patients with skin disease between 1815 and 2000 had scabies; the prevalence during wartime reached over 30%.³

ETIOLOGY AND PATHOPHYSIOLOGY

• Human scabies is caused by the mite Sarcoptes scabiei, an obligate human parasite: without contact with human skin, the scabies mite can live only 24–36 hours (Figure 149-3).^1,4

• Adult mites spend their entire life cycle, around 30 days, within the epidermis. After copulation the male mite dies and the female mite burrows through the superficial layers of the skin, excreting feces (Figure 149-4) and laying eggs (Figure 149-5), which then hatch and repeat the cycle.⁵

• Mites move through the superficial layers of skin by secreting proteases that degrade the stratum corneum.

• Infected individuals usually have fewer than 100 mites. In contrast, immunocompromised hosts, those with HIV, older patients, and people affected with Down syndrome⁵ can have up to 1 million mites and are susceptible to crusted scabies (Figures 149-6, 149-7, 149-8, 149-9).¹

• Transmission usually occurs via direct skin contact. Scabies in adults is frequently sexually transmitted.⁶ Scabies mites can also be transmitted from animals to humans.¹

• Mites can also survive for 3 days outside of the human epidermis, allowing for infrequent transmission through bedding and clothing.

• The incubation period is on average 3 to 4 weeks for an initial infestation. Sensitized individuals can have symptoms within hours of reexposure.

RISK FACTORS

• Scabies is more common in young children, healthcare workers, homeless and impoverished persons, and individuals who are immunocompromised or suffering from dementia.¹

• Institutionalized individuals and those living in crowded conditions also have a higher incidence of the infestation.¹

DIAGNOSIS

CLINICAL FEATURES

• Pruritus is a hallmark of the disease.¹

• Skin findings include papules (see Figure 149-9), burrows (Figures 149-10 and 149-11), nodules (Figure 149-12), and vesiculopustules (Figure 149-13).

• Burrows are the classic morphologic finding in scabies and the best location to find the mite (see Figures 149-10 and 149-11).

• Infants and young children can also exhibit irritability and poor feeding.

• Pruritic papules/nodules around the axillae (see Figure 149-12) or umbilicus, or on the penis and scrotum (Figures 149-14 and 149-15), are highly suggestive of scabies.

TYPICAL DISTRIBUTION

• Classic distribution in scabies includes the interdigital spaces (see Figures 149-10 and 149-11), wrists (see Figure 149-6), ankles, waist (Figure 149-16), groin, axillae, palms, and soles.

• Genital involvement can also occur. Especially on the penis (see Figures 149-14 and 149-15).

• In young children, the face and head can also be involved (Figure 149-17).

LABORATORY STUDIES AND IMAGING

• Light microscopy of skin scrapings provides a definitive diagnosis when mites, eggs, or feces are identified (see Figures 149-3, 149-4, 149-5). This can be challenging and time-consuming, even when mites, eggs, or feces are present. Packing-tape stripping of skin has also been used instead of a scalpel to find mites for examination under the microscope.⁷

• Dermatoscopy is a useful and rapid technique for identifying a scabies mite at the end of a burrow. The mite has been described as a jet plane (delta wing) with a contrail (Figure 149-18). The advantage of the dermatoscope is that multiple burrows can be examined quickly without causing any pain to the patient. Children are more likely to stay still for this than scraping with a scalpel or skin stripping with tape.

• If a dermatoscope is available, start with this noninvasive examination.⁸ If the findings are typical, then a microscopic examination is not needed. If the findings are not convincing, or a dermatoscope is not available, perform a scraping. It is best to scrape the skin at the end of a burrow. Use a #15 scalpel that has been dipped into mineral oil or microscope immersion oil. Scrape holding the blade perpendicular to the skin until the burrow (or papule) is opened (some slight bleeding is usual). Transfer the material to a slide and add a coverslip.

• Tips for microscopic examination—Start by examining the slide with the lowest power available, as mites may be seen under 4× power, and the slide can be scanned most quickly with the lowest power. If no mites are seen switch to 10× power and scan the slide again looking for mites, eggs, and feces. Forty power may be used to confirm findings under 10× power.

• One study comparing dermatoscopic mite identification with microscopic examination of skin scrapings found the former technique to be of comparable sensitivity (91% and 90%, respectively) with specificity of 86% vs. 100%, even in inexperienced hands.⁹ Another study reported sensitivity of dermatoscopy at 83%.¹⁰ In this study, the negative predictive value was identical for dermatoscopy and the adhesive tape test (0.85), making the latter a good screening test as long as a microscope is available.

• Video dermatoscopy can also be used to diagnose scabies.¹¹ Video dermatoscopy allows for higher skin magnification than standard dermatoscopy but at a much greater cost for equipment.

• S. scabiei recombinant antigens have diagnostic potential and are under investigation for identifying antibodies in individuals with active scabies.¹²

BIOPSY

Rarely necessary unless there are reasons to suspect another diagnosis.

DIFFERENTIAL DIAGNOSIS

• Bed bugs live in the sleeping area and feed on people sleeping in their beds (Figure 149-19). Therefore, the pruritic papules of bed bug bites tend to appear in the morning. The skin manifestations of these bites can appear anywhere on the body, especially in skin not covered by pajamas. The bites may occur in a linear pattern of 3 bites in a row (Figure 149-20). The mnemonic for this is breakfast, lunch, and dinner. However, bed bug bites do not have to follow this pattern. Bed bug bites do not follow the typical scabetic pattern and will not show burrows in the skin. If bed bugs are suspected, it is best to have a professional come out to investigate for their presence.

• Arthropod bites—Bites may exhibit puncta that allow for differentiation from scabies. They usually don't follow the typical scabies distribution. Consider body lice as a possible diagnosis if the patient is living on the streets or in a homeless shelter. Look for the lice in the seams of the clothing rather than on the skin (see Chapter 148, Lice).

• Acropustulosis of infancy—A vesiculopustular recurrent eruption limited to the hands, wrists, feet, and ankles. It is rare after 2 years of age (see Chapter 116, Pustular Diseases of Childhood).

• Cutaneous larva migrans (CLM)—The serpiginous burrows of CLM may be mistaken for scabies burrows. CLM tends to have longer serpiginous lesions than does scabies. Also, the lesions of CLM are found in areas of the skin that have contacted soil contaminated by feces containing hookworm larvae (see Chapter 150, Cutaneous Larva Migrans).

• Dermatitis—All kinds of dermatitis (atopic dermatitis, contact dermatitis, seborrheic dermatitis, and drug eruptions) with pruritus can be mistaken for scabies. A good history and physical exam should help to distinguish the various patterns of dermatitis from scabies.

MANAGEMENT

FIRST LINE

• Treatment consists of administration of a scabicide and an antipruritic.^1,13 The two most commonly used scabicidal medications are permethrin and ivermectin (see Table 149-1 comparing these two medications). Antipruritic medications are typically oral antihistamines as needed.

• All household or family members living in the infested home and their sexual contacts should be simultaneously treated. SORⒸ Failure to treat all involved individuals often results in recurrent infestation within the family. Use of insecticide sprays and fumigants is not recommended.

• Environmental decontamination is a standard component of all therapies. SORⒷ Clothing, bed linens, and towels should be machine washed in hot water. Clothing or other items (e.g., stuffed animals) that cannot be washed may be dry cleaned or stored in sealed bags for at least 72 hours.

• Topical permethrin—First-line therapy often begins with topical permethrin 5% cream. Permethrin 5% cream is the most effective treatment based on a systematic review in the Cochrane database.¹³ SORⒶ It has the advantages of having a quick onset of action and FDA approval for scabies. The cream should be applied before bed to all areas from neck down in adults and children and head to toe in infants. Make sure to get under all fingernails and toenails, while sparing the eyes and mouth if applied to the face. The cream should be washed off 8 to 14 hours later. Repeat treatment is often recommended in 7 to 10 days. In patients with crusted scabies, use of a keratolytic cream may facilitate the breakdown of skin crusts and improve penetration of the cream.¹⁴ Unfortunately, scabies resistance to permethrin is increasing. Although permethrin is now available generically, the prescription cost is still high.

• Oral ivermectin is available in 3 and 6 mg tablets and is prescribed as a single dose based on weight (0.2 mg/kg).¹³ SORⒷ Dosing often needs to be rounded up to accommodate the use of whichever tablets are available. The need for a second dose at 7–10 days is debated, and the evidence for this is not strong. It is recommended that the tablets be taken with food to enhance absorption.¹⁴ Although ivermectin is routinely prescribed for scabies, it is not FDA approved for this indication. It is not recommended in children weighing less than 15 kg.

SECOND LINE

• Other topical treatments include crotamiton, benzyl benzoate, malathion, and sulfur in petrolatum.¹³

• Lindane is no longer used in the United States. It is contraindicated for infants because of high risk for neurotoxicity, seizures, and aplastic anemia. It is also contraindicated in pregnancy.

• Symptomatic treatment with antipruritics such as diphenhydramine, hydroxyzine, and mid-potency steroid creams can be used for symptom management. SORⒸ

• Antibiotics are needed if there is evidence of a bacterial superinfection (see Figure 149-7). SORⒸ

Special populations:

• Infants—First-line therapy in infants is topical permethrin 5% cream. However, in infants younger than 2 months of age, a sulfur preparation is recommended as safe.^14,15 It is used as 5% to 10% precipitated sulfur in petrolatum and applied as described earlier for permethrin. Unfortunately, it has a bad odor.

• Elderly—First-line treatment for geriatric patients with scabies is either oral ivermectin or topical 5% permethrin cream. In elderly patients topical permethrin should also be applied to the scalp and face, as mites can infest the hairline and forehead in these patients. Patients should be advised to avoid applying cream to the eyes and mouth.¹⁵

• Pregnant women—First-line treatment in pregnancy is permethrin 5% cream, which is classified as category B in pregnancy; no category A treatments are available. Second-line treatments include topical sulfur and benzyl benzoate. Ivermectin is not recommended in pregnancy as it is category C.

• Breastfeeding women—Permethrin 5% cream is the drug of choice for breastfeeding women because there is no known risk to infant safety. Ivermectin is not recommended due to inadequate data on infant safety.

• Crusted scabies (severe scabies with crusting especially on the hands and feet)—The patient may be immunosuppressed and there are many more mites present, so the CDC recommends the use of both oral ivermectin and topical permethrin together.¹⁵ SORⒸ Depending on the severity of the crusted scabies, the oral ivermectin may be prescribed in three doses (approximately days 1, 2, and 8), five doses (approximately days 1, 2, 8, 9, and 15), or seven doses (approximately days 1, 2, 8, 9, 15, 22, and 29).¹⁵ SORⒸ The CDC also recommends prescribing the topical permethrin to be applied overnight every 2–3 days for 1–2 weeks to treat crusted scabies.¹⁵ SORⒸ

COMPLEMENTARY AND ALTERNATIVE THERAPY

• Tea tree oil contains oxygenic terpenoids, found to have rapid scabicidal activity.⁵

• Anise seed oil displays antibacterial and scabicidal activity and is used topically, but should not be used in pregnancy.¹⁶

PREVENTION

• Avoid direct skin-to-skin contact with an infested person or with items such as clothing or bedding used by an infested person.

• Treat members of the same household and other potentially exposed persons at the same time as the infested person to prevent possible reexposure and reinfestation.

• Prophylactic treatment to prevent infestation of those with skin-to-skin contact has been shown by Cochrane database to have unknown outcomes.¹⁷

• Oral ivermectin may reduce the prevalence of scabies at 1 year in populations with endemic disease more than topical permethrin.¹⁸ SORⒷ

PROGNOSIS

• The prognosis with proper diagnosis and treatment is excellent unless the patient is immunocompromised; reinfestation, however, often occurs if environmental risk factors continue.¹

• Postinflammatory hyper- or hypopigmentation can occur.¹

FOLLOW-UP

• Routine follow-up is indicated when symptoms do not resolve.

• Consider an immunologic work-up for individuals with crusted scabies.

PATIENT EDUCATION

• Patients should avoid direct contact including sleeping with others until they have completed the first application of the medicine.

• Patients may return to school and work 24 hours after first treatment.

• Patients should be warned that itching may persist for 1 to 2 weeks after successful treatment but that if symptoms are still present by the third week, the patient should return for further evaluation.

REFERENCES

PATIENT STORY

A mother brought her 18-month-old son to the physician's office for an itchy rash on his feet and buttocks (Figures 150-1 and 150-2).¹ The first physician examined the child and made the incorrect diagnosis of tinea corporis. The topical clotrimazole cream failed. The child was unable to sleep because of the intense itching and was losing weight secondary to his poor appetite. He was taken to an urgent care clinic, where the physician learned that the family had returned from a trip to the Caribbean prior to the visit to the first physician. The child had played on beaches that were frequented by local dogs. The physician recognized the serpiginous pattern of cutaneous larva migrans (CLM) and successfully treated the child with oral ivermectin. The child was 15 kg, so the dose was 3 mg (0.2 mg/kg), and the tablet was ground up and placed in applesauce.

SYNONYMS

Creeping eruption, plumber's itch.

EPIDEMIOLOGY

• Endemic in developing countries, particularly Brazil, India, South Africa, Somalia, Malaysia, Indonesia, and Thailand.^2,3

• Peak incidence in the rainy seasons.³

• During peak rainy seasons, the prevalence in children is as high as 15% in resource-poor areas, but much less common in affluent communities in these same countries with only 1 to 2 per 10,000 individuals per year.⁴

• In the United States, it is found predominantly in Florida, southeastern Atlantic states, and the Gulf Coast.²

• Children are more frequently affected than adults.⁴

ETIOLOGY AND PATHOPHYSIOLOGY

• Caused most commonly by dog and cat hookworms (i.e., Ancylostoma braziliense, Ancylostoma caninum, Uncinaria stenocephala).⁴

• Eggs are passed in cat or dog feces.²

• Larvae are hatched in moist, warm sand/soil.²

• Infective-stage larvae penetrate the skin.²

DIAGNOSIS

The diagnosis is based on history and clinical findings.

CLINICAL FEATURES

• Elevated, serpiginous, or linear reddish-brown tracks 1 to 5 cm long (Figures 150-1, 150-2, 150-3).^2,5

• Intense pruritus, which often disrupts sleep.³

• Symptoms last for weeks to months, and, rarely, years. Most cases are self-limiting.⁵

TYPICAL DISTRIBUTION

• Feet and lower extremities (73%), buttocks (13% to 18%), and abdomen (16%).^6,7

• Areas that come in contact with contaminated skin.

  • Most commonly the feet, buttocks, and thigh.³

LABORATORY AND IMAGING

• Not indicated, but rarely blood tests shows eosinophilia or elevated immunoglobulin E levels.⁵

DIFFERENTIAL DIAGNOSIS

May be confused with the following conditions:

• Cutaneous fungal infections—Lesions are typically scaling plaques and annular macules with central clearing. If the serpiginous track of CLM is circular, this can lead to the incorrect diagnosis of "ringworm." The irony is that ringworm is a dermatophyte fungus whereas CLM really is a worm (see Chapter 144, Tinea Corporis).

• Contact dermatitis—Differentiate by distribution of lesions, presence of vesicles, and absence of classical serpiginous tracks (see Chapter 152, Contact Dermatitis).

• Erythema migrans of Lyme disease—Lesions are usually annular macules or patches and are not raised and serpiginous (see Chapter 227, Lyme Disease).

• Phytophotodermatitis—The acute phase of phytophotodermatitis is erythematous with vesicles; this later develops into postinflammatory hyperpigmented lesions. This may be acquired while preparing drinks with lime on the beach and not from the sandy beach infested with larvae (see Chapter 208, Photosensitivity).

MANAGEMENT

• Ivermectin (Stromectol) lacks FDA indication, but has been well studied and is the current drug of choice.³

  • A single dose of ivermectin 0.2 mg/kg is recommended.³ SORⒷ

  • Cure rates of 77% to 100% with a single dose.⁸

  • Ivermectin has been used worldwide on millions with an excellent safety profile.³

  • Ivermectin is contraindicated in pregnancy, in breastfeeding mothers, and in children weighing less than 15 kg.³

• Albendazole has been successfully prescribed for more than 25 years and is the Centers for Disease Control and Prevention (CDC) drug of choice.⁵

  • Albendazole also lacks FDA indication, and the recommended dose is 400 mg daily for 3 to 7 days.^3,5

  • Cure rates with albendazole exceed 92%, but it is less with single dosage.³

  • Studies on compounded ivermectin and albendazole for topical use are limited, but promising for use in children.³

• Oral thiabendazole was the first proven therapy with FDA approval. It was removed from the U.S. market in 2010 but continues to be used outside the United States.

ADJUNCT THERAPY

• Antihistamines may relieve itching.

• Antibiotics may be used if secondary infection occurs.

PATIENT EDUCATION

• Wear shoes on beaches where animals are allowed.

• Keep covers on sand boxes.

• Pet owners should keep pets off the beaches, deworm pets, and dispose of feces properly.

FOLLOW-UP

• Follow up if lesions persist.

REFERENCES