Chapter 13: Infestations and Bites

Arthropods have always feasted on humans and humans have tried countless strategies to keep them from doing so. The societal burden of biting and sucking bugs is significant, costing millions of dollars, tremendous discomfort, and immeasurable emotional distress. They bite, we itch, we scratch, and these facts seem destined to endure.

Introduction

Scabies is a common parasitic infection caused by the mite Sarcoptes scabiei var hominis. Transmission is primarily person-to-person by direct contact and although anyone is susceptible, situations that result in more skin-to-skin contact, such as parents with small children, sexual activity, overcrowding, and institutional settings, increase the incidence of infestation. Although the scabies mite has not been shown to transmit any significant pathogens, the intense itching associated with the infestation, the risk of superinfection of excoriated skin, and the fact that up to 300 million people may be affected worldwide annually make scabies a significant public health problem.¹

Pathophysiology

Sarcoptes scabiei is an obligate human parasite that completes its entire 30-day life cycle within the epidermis. The fertilized female weaves through the epidermis and leaves a trail of 60 to 90 eggs and feces (scybala), in her burrow (Figure 13-1). The eggs hatch into larvae that then mature into nymphs and adults. The rash and pruritus of scabies is a result of a hypersensitivity reaction to the mite and its detritus. The incubation period from infestation to pruritus can range from days to months. The first time an individual is infested, it typically takes 2 to 6 weeks to become sensitized and develop symptoms, but in subsequent infestations, the previously hypersensitized individual can begin itching in as little as 1 to 3 days. Some infested individuals never develop hypersensitivity to the mite and never experience symptoms, but can still transmit the infection; these are asymptomatic "carriers."

Clinical Presentation

History

Intense pruritus is the main presenting complaint, although very young children who cannot verbalize itching are often irritable and eat and sleep poorly. Adults often complain that the pruritus is worse at night. Family members and close contacts frequently report similar symptoms.

Physical Examination

The patient presenting with scabies usually has a nondescript, excoriated, papular dermatitis. The most common physical findings are papules, vesicles, pustules, or nodules. These typically occur on the trunk, arms, hands (Figures 13-2 and 13-3), and genitals in adults and may also involve the head, neck, and feet in infants and young children (Figures 13-4 and 13-5). The burrow, a short, wavy line, is pathognomic of scabies and is typically seen on the wrists, finger webs, and penis (Figures 13-1 and 13-3).

Less common presentations include nodular, bullous, and crusted scabies.²

• Nodular scabies: This typically presents with a few salmon-colored pruritic nodules usually seen in the axillae, groin, and male genitalia. Nodular scabies is a hypersensitivity reaction that typically occurs after a successfully treated scabies infestation and does not necessarily indicate active infection.

• Bullous scabies: While blisters commonly occur on the palms and soles of infants infested with scabies, bullous scabies is a more extensive bullous eruption, most commonly seen in elderly adults. It is often confused with bullous pemphigoid.

• Crusted (Norwegian) scabies: This presents with thick, crusted or scaly plaques and is often confused with psoriasis. Crusted scabies typically affects the immunocompromised, elderly, disabled, or debilitated individuals. These patients often do not exhibit typical pruritus and scratching and are often infested with thousands of mites. They are highly contagious.

Laboratory Findings

Table 4-3 has instructions for collection and examination of a scabies preparation. The presence of a mite, eggs, or scybala in a scabies preparation confirms the diagnosis (Figures 13-6 and 13-7). Scraping the skin for a scabies specimen is not always easy to do without injuring the patient, particularly if that patient is a squirming child; therefore, other identification techniques have been suggested. Dermoscopy has shown to be a sensitive tool for mite identification.³ Another method is to firmly apply adhesive tape to a burrow, pull it off rapidly and then transfer the tape to a slide for microscopic identification. This has also been shown to be an inexpensive, easy and relatively sensitive way to identify burrow contents.³

Diagnosis

The key diagnostic features of scabies are intensely pruritic papules, vesicles or burrows in the finger webs, wrists, breast, axillae, abdomen, or genitals. In children, the lesions can be in any location including the head, neck, or feet.

Differential Diagnosis

Scabies should be considered in the differential diagnosis of any patient who presents with an intensely pruritic, eczematous rash of recent onset, especially if family members and other close contacts have similar complaints. Scabies is often misdiagnosed as the following diseases.

• ✓ Atopic dermatitis: Presents with scaly, often crusted, pruritic papules and plaques on the face, and flexural areas in patients with a personal or family history of atopy. Scabies may be difficult to diagnose in patients who have moderate to severe atopic dermatitis.

• ✓ Body and pubic lice: Presents with pruritus and lice on the body or clothing.

• ✓ Other arthropod bites: There are no burrows present.

• ✓ Dermatitis herpetiformis: Presents with lesions very similar to scabies on the elbows, knees, and lower back. The genitals are not affected.

• ✓ Other: Fiberglass dermatitis, tinea corporis, drug rash, lichen planus, contact dermatitis, dyshidrotic dermatitis, prurigo, delusions of parasitosis, acropustulosis of infancy.

Management

Scabies is usually a clinical diagnosis. A patient can be treated based on a suspicious history and clinical presentation. Prescription scabicides are necessary to treat scabies. No over the counter medications are approved for scabies treatment. Table 13-1 outlines scabies treatment options. Permethrin 5% cream is the most effective treatment, according to the Cochrane Review which has the largest review of interventions for treating scabies.⁴ The cream should be applied at bedtime and spread thoroughly from neck to soles, including under the fingernails and toenails. In children under two, permethrin cream should also be applied to the head and neck and mittens or socks should be placed on the hands to avoid rubbing the cream into the eyes. Patients should remove the cream after 8 to 14 hours by showering or bathing. Oral ivermectin, although not approved by the Federal Food and Drug Administration (FDA) for the treatment of scabies, is easier to use and may result in improved treatment compliance. Two doses of ivermectin are required to achieve cure rates equivalent to one application of permethrin cream.⁵ Crusted scabies requires a more aggressive approach, with a combination of 5% permethrin every 2 to 3 days for up to 2 weeks and oral ivermectin in 3 to 7 doses over approximately 1 to 4 weeks, depending on the severity of infection.⁵

Fomite transmission is not considered a major problem in typical scabies infestations and scabies mites generally do not survive more than 2 to 3 days off human skin. Bedding, clothing, and towels used by infested persons or their close contacts anytime during the 3 days before treatment should be washed in hot water and dried in a hot dryer, dry-cleaned or sealed in a plastic bag for at least 72 hours. Persons who had close contact with an infested individual should be evaluated and treated appropriately.

The pruritus from scabies is a result of patient hypersensitivity and neither the immune response nor the itching resolves immediately after treatment. Patients should be advised that it takes up to 4 weeks for symptoms to resolve despite effective treatment. If pruritus persists beyond a month, the patient should be reexamined and if evidence of active infestation is present, the possibilities of poor treatment compliance, reinfestation, or mite scabicide resistance should be considered and addressed.

Indications for Consultation

If symptoms persist despite two courses of appropriate therapy, consider dermatologic consultation. A number of eczematous and vesiculobullous conditions can mimic the presenting signs and symptoms of scabies and occasionally scabies treatment can cause secondary dermatologic sequelae that require intervention.

Patient Information

• Scabies. Centers for Disease Control: www.cdc.gov/parasites/scabies/biology.html

• Scabies Tutorial. Medline Plus. National Institutes of Health: www.nlm.nih.gov/medlineplus/tutorials/scabies/htm/index.htm

• Scabies. American Academy of Dermatology: www.aad.org/skin-conditions/dermatology-a-to-z/scabies

Introduction

Human lice are bloodsucking, wingless insects that have been feeding on mankind for thousands of years.² Head, crab, and body lice remain a bane in modern times, with hundreds of millions of cases of pediculosis worldwide annually.

Head lice are the most common of the three pediculosis and are a ubiquitous nuisance. They are found in people of all age, sex, race, and socioeconomic class. School children ages 3 to 11, especially girls with long hair and a propensity to share hair care tools and accessories, are at greatest risk. African-American children are less commonly affected, perhaps because their hair shape or texture creates a less amenable environment for lice survival and reproduction.⁶

Crab (pubic) lice are transmitted primarily by sexual contact and the highest incidence is seen in men who have sex with men, ages 15 to 40.

Body lice give all lice a bad name. Not only are they associated with poor hygiene, they serve as disease vectors for epidemic typhus, relapsing fever, trench fever, and bacillary angiomatosis or endocarditis.^2,7

Pathophysiology

All three lice species are obligate human parasites that feed exclusively on human blood and do not survive for long off their human host. They vary in size, shape, and preference for body area location.

• The head louse, Pediculosis capitis, as the name suggests, favors scalp hair. It is light tan to medium brown and is about the size of a sesame seed (Figure 13-8). Although it is unable to jump or fly, it moves extremely quickly and thus can be difficult to see. The female louse lives about 30 days and lays 5 to 10 eggs a day. Oval egg capsules or nits are cemented to hair shafts close to the scalp for warmth (Figure 13-9). Transmission is via direct contact or by fomites such as combs, brushes, hats, helmets, headphones; although static electricity and blow dryers have been shown to launch lice into the air, creating another possible mode of transmission.⁸

• Crab lice, Phthirus pubis, are smaller and wider than head lice and resemble tiny crabs. (Figure 13-10). Often referred to as pubic lice, this is a misnomer; as crab lice are adapted to ambulate over the entire body surface. The infestation can involve not only pubic hair, but also the scalp, eyebrows, eyelashes, moustache, beard, axillae, and perianal area.

• The body louse, Pediculosis corporis, at 2 to 4 mm long, is slightly larger than the head louse, but otherwise looks similar. It differs from head and crab lice in that while it feeds on humans it does not live on them; it lives in clothing and lays its eggs along the seams (Figure 13-11).

Clinical Presentation

History

A patient with lice will usually present with intense itching in the area of infestation, and a history compatible with exposure.

Physical Examination

Clinical findings are nonspecific eg, erythema, papules, wheals, excoriations, hemorrhagic crusts, and occasionally scale. The occipital scalp, posterior ears, and neck are the most common sites involved with head lice; lower abdomen, pubic area, and thighs with crab lice; and back, neck, shoulders, and waist with body lice. Pyoderma and regional lymphadenopathy may be present. Macula cerulea, small bluish dots, may be seen at the site of lice and flea bites.

Nits may be seen on examination of proximal hair shafts or on clothing seams in cases of body lice. Identifying a live louse is the only way to make a definitive diagnosis of active infection, but since lice shy away from light and move very quickly, this is not easy to do. Systematically wet-combing detangled and lubricated hair with a specially designed nit comb has been shown to be a sensitive method to harvest and identify live lice.⁹

Laboratory Findings

A skin biopsy demonstrates nonspecific inflammation.

Diagnosis

The key diagnostic features of pediculosis are the presence of lice or nits on hair, skin or clothing seams.

Differential Diagnosis

For body and crab lice

• ✓ Scabies, flea bites, other arthropod bites, atopic dermatitis, and folliculitis.

For head lice

• ✓ Seborrheic dermatitis, residual hair styling products, and hair casts.

Management

• Body lice are usually successfully treated by bathing the patient and bagging and discarding infested clothing and bed linen. If clothing cannot be discarded, it can be washed in hot water (at least 149°F) for 30 minutes, dry cleaned or hot ironed (especially in seams). If nits are found on body hair, the best treatment option is a single 8- to 10-hour application of 5% permethrin cream to the entire body, similar to scabies treatment.¹⁰

• Crab lice can be treated topically with 1% and 5% permethrin cream or 1% lindane shampoo. The safest and most effective topical treatment is 5% permethrin cream applied overnight to all hair bearing- areas, washed off in the morning, and repeated 1 week later. Topical pediculocides cannot be applied to the eyelashes and treating this area is challenging. If possible, nits and lice can be physically removed with fingernails or a nit comb or ophthalmic-grade petrolatum ointment (only available by prescription) can be applied to the eyelid margins 2 to 4 times a day for 10 days. Regular petrolatum jelly (Vaseline) should not be used in this location because it can irritate the eyes.¹⁰ Oral ivermectin is not FDA-approved for crab lice, but has been suggested for patients with perianal or eyelid involvement or when topical treatment fails. The recommended dose is 200 mcg/kg, repeated 1 week later.¹¹ Individuals with crab lice should be evaluated for sexually transmitted diseases that often occur concomitantly.

• Head lice management can be challenging. Pediculocides remain the mainstay of treatment, but increased resistance to therapy, both by parents who are concerned about safety and by lice that have evolved to withstand insecticides, often confounds the health care provider. Pediculocides, currently employed for the treatment of head lice, are reviewed in Table 13-2. Many other treatments have been suggested. Trimethoprim-sulfamethoxazole has been studied in small trials and is recommended in combination with 1% permethrin for use in cases of multiple treatment failures or suspected lice resistance.⁷ Removal by fingers, nit combs, "bug-buster" combs, and commercially available "egg-removal" products, when studied, has been suboptimal in obtaining cure.⁹ Of the home-remedy occlusive agents (eg, petroleum jelly, mayonnaise, margarine, olive oil, etc.), petroleum jelly has shown the most success, although the Centers for Disease Control and Preventions (CDC) has reported that there is no clear scientific evidence that any of these are effective. Shaving the hair has been suggested as a chemical-free treatment option, but it can be emotionally traumatic for the child.⁸ Most studied treatments kill live lice and not nits and need to be repeated a week after the first application to treat newly hatched lice. Although most treatments need to be repeated 1 week after the first, there are two exceptions.

(1) Malathion kills live lice and nits and it should be repeated only if live lice are noted. (2) Lindane which is not a first-line treatment for head lice should be used for one treatment only because of its toxicity. Parents, caregivers, or patients should be instructed to carefully read and follow the patient medication guidelines in the package inserts of pediculocides. Clothing and linen used in the 2 days before treatment should be washed and dried at the hottest temperatures the fabrics can withstand, dry cleaned or sealed in plastic bags for 2 weeks. Hair grooming utensils should be soaked in hot water (130°F) for 5 to 10 minutes and the floor and furniture vacuumed.¹⁰ Although the presence of nits often creates anxiety, current consensus is that affected children may return to school after their first treatment. The presence of nits should not exclude school attendance.^7,8

Indications for Consultation

Consultation should be considered when live lice persist after two appropriate treatments or when symptoms persist beyond 4 to 6 weeks. Patients should be advised that it may take a number of weeks for symptoms to abate even when the lice have been successfully treated and that the persistence of nits does not imply persistent active infection.

Patient Information

Lice. Centers for Disease Control: www.cdc.gov/parasites/lice/

Introduction

Lyme disease is caused by Borrelia, a spirochete transmitted by Ixodes ticks. In North America, 90% of cases occur on the east coast between the states of Maine and Maryland and in Minnesota and Wisconsin.¹³ Borrelia species also cause disease in central and eastern Europe and eastern Asia. The incidence of Lyme disease peaks in patients between the ages of 5 to 19 years and 55 to 69 years. The onset of Lyme disease usually occurs from May to November with a peak in June, July, and August. Erythema migrans is the characteristic annular plaque of Lyme disease (Figure 13-12).

Pathophysiology

Borrelia burgdorferi causes most cases of Lyme disease in North America. The deer tick, Ixodes Scapularis, is the most common vector for Lyme disease (Figure 13-13). This tick has a 2-year life cycle with larval, nymphal, and adult stages. The ticks feed once during each stage on various hosts and may acquire B. burdorferi while feeding on an infected host. The white-tailed deer and white-footed mouse are common hosts, but other species of birds, mice, rats, raccoons, and rabbits may also be hosts. In humans the affected tick usually has to be attached and feeding for 48 to 72 hours to transmit the Borrelia organism.¹⁴ Ixodes nymphs cause most of cases of Lyme disease. The nymphs are the size of a pinhead (2 mm or less), so they may go undetected while attached to human skin.¹⁴

Clinical Presentation

History

Typically patients have a history of being in a wooded or grassy area in an endemic region within the past month. However, many patients will not recall having a tick bite.

  Lyme disease can progress through three stages.

• Early localized stage (3 to 30 days after bite): 50% of adults and 90% of children will present with erythema migrans 3 to 30 days (average 7 days) after the bite.¹⁴ Influenza like symptoms (headache, fatigue, myalgia, and fever), lymphadenopathy, and conjunctivitis may be present.

• Early disseminated stage (days to weeks later): Neurological symptoms such as severe headaches, neck stiffness, and Bell's palsy may develop. Pain and swelling in large joints and cardiac symptoms may also occur.

• Late disseminated stage (months to years later): About 10% to 20% of patients with Lyme disease will have chronic arthritis or neurological symptoms.¹⁴

Physical Examination

The initial lesion of erythema migrans is a pink macule that rapidly expands to a diameter of about 15 cm, although the range can be from 3 to 68 cm (Figure 13-12). Often there is central clearing, but the lesion may be uniform throughout. The initial lesion is at the site of the bite and is usually located on the legs, trunk, groin, or axillae. In children, common sites include the head and neck. Erythema migrans resolves without treatment within 4 to 6 weeks.¹⁴

Laboratory Findings

Serologic testing may be done in patients who have a high likelihood of Lyme disease. However, false-negative results can occur if the tests are done too early in the course of the disease. False positives can occur in patients who live in endemic areas. The Centers for Disease Control and Prevention (CDC) publishes specific recommendations for serological testing (Figure 13-14).¹⁵

While the histopathologic features of erythema migrans are not specific, a skin biopsy obtained from the periphery of the lesion may be helpful in differentiating it from other similar appearing skin lesions, and a Warthin–Starry stain can sometimes demonstrate Borrelia spirochetes in the skin.¹⁶

Diagnosis

The CDC classifies Lyme disease as confirmed, probable, or suspected. Confirmed Lyme disease requires

• A case of erythema migrans with known exposure (having been in a woody, brushy, or grassy area in an endemic county ≤30 days prior), or

• A case of erythema migrans without known exposure but with a qualified laboratory assay demonstrating evidence of infection, or

• A case with at least one late manifestation that has laboratory evidence of infection.¹⁵

A probable case is any other physician-diagnosed Lyme disease that has laboratory evidence of infection and suspected Lyme disease is a case of erythema migrans with no known exposure and no supportive laboratory assay, or a case with laboratory evidence but no available clinical information.

Differential Diagnosis

• ✓ Bites from ticks, mosquitoes, bees, and wasps: Typically the erythema associated with these bites does not exceed 5 cm in diameter.

• ✓ Erysipelas or cellulitis: The white blood cell count may be elevated and often the area is tender and there is no central clearing.

• ✓ Herald patch of pityriasis rosea: The diameter does not usually exceed 5 cm and there is a ring of scale within the lesion.

• ✓ Other: Fixed drug rash, tinea corporis, dermatitis, granuloma annulare, and erythema multiforme.

Management

Treatment depends on the stage of the disease, the age of the patient, and relative contraindications associated with the recommended medications. The Infectious Disease Society of America (ISDA) publishes guidelines for Lyme Disease Management (Tables 13-3 and 13-4).¹⁷

Macrolide antibiotics are not recommended as first-line therapy, first-generation cephalosporins are ineffective, and ceftriaxone, while effective, is not superior to oral agents and has more side effects, so is not recommended unless other agents are contraindicated.¹⁷

Instructions for prevention of Lyme disease are as follows:¹⁵

• When possible avoid areas with long grass and bushes in tick-infested locales.

• Wear light-colored shirts and long pants with socks covering the bottom of the pants.

• Use insect repellents with 20% to 30% DEET.

• Perform thorough full body tick checks once or twice a day.

• Check clothing, gear, and pets for ticks.

• If a tick is found on the body, grasp the tick with tweezers as close to the skin as possible and gently pull the tick's body away from the skin. Clean the area with soap and water.

• The CDC site for Lyme disease has additional information on tick removal and landscaping techniques to control ticks.

Indications for Consultation

The diagnosis and treatment of post-treatment Lyme disease syndrome is controversial. When this diagnosis is considered a rheumatologic or infectious disease, consult should be considered before therapy initiated.¹⁵

Patient Information

• Centers of Disease Control and Prevention Lyme disease page: www.cdc.gov/lyme/

• State of Connecticut Department of Public Health Lyme Disease page: www.ct.gov/caes/lib/caes/documents/publications/.../b1010.pdf

• Mayo clinic: www.mayoclinic.com/health/lyme-disease/DS00116

Introduction

Although the bed bug, Cimex lectularius, has been a known human parasite for thousands of years, developed countries experienced a near 50-year hiatus from this pest, when it was almost eradicated from North America as a result of mass treatments with insecticides such as dichlorodiphenyltrichloroethane (DDT), Chlordane, and hexachlorocyclohexane (Lindane).¹⁸ Bed bugs are back for a number of possible reasons, including increased international travel, immigration, changes in pest control practices, and insecticide resistance. Bed bugs can be found in settings from 4-star hotels to homeless shelters. Anyone is a potential target.

Pathophysiology

Adult bed bugs are brown, oval, wingless somewhat flat insects about the size of an apple seed (Figure 13-15). As they feed, they grow in length from about 5 to 9 mm and change from brown to purple red. Young bugs are smaller and nearly colorless. Bed bugs usually hide during the day and feed at night. They are attracted to heat and carbon dioxide and feed on exposed skin. They then move back to their hiding places, typically mattress and box spring seams (Figure 13-16), bed frames, or bedroom furniture, although they can hide almost anywhere.¹⁹ It is in these hiding places where the wary traveler can find evidence of a bed bug infestation, by the presence of dead bugs, feces, and molted skin casings (Figure 13-16). Bed bugs are resilient; they can survive up to a year or more without a blood meal. Although they have been implicated in the transmission of infectious diseases such as Hepatitis B, evidence for disease transmission is equivocal and their significance as disease vectors has yet to be established.¹⁹

Clinical Presentation

History

While anyone can be a victim of bed bug bites, a suggestive history might include living in a known infested environment, recent acquisition of a used mattress or couch, or travel to a potentially infested destination. The pest control company, Terminix compiles an annual list of the Top 15 Most Bed Bug Infested US Cities. In 2012, the top five were Philadelphia, Cincinnati, New York, Chicago and Detroit.²⁰

Physical Examination

Clinical manifestations vary from no reaction to typical appearing insect bites to papular urticaria or bullous reactions. While the bite appearance is not specific, bite distribution is often suggestive of bed bugs. The most commonly involved areas are those that are typically exposed while sleeping such as the scalp, face, neck, and arms (Figure 13-17). The timing between possible exposure and the development of the bites is not always diagnostic. One researcher, using himself as a once-weekly blood meal for bed bugs, noted that the time it took from bug bite to immune response progressed from delayed to immediate over the 7 years he studied his exposure.¹⁹ Occasionally patients present with dermatitis or secondary infection at the bite sites. A few studies have suggested that bed bug bites may cause systemic reactions such as asthma, generalized urticaria, and anaphylaxis.¹⁹

Laboratory Findings

Lab results are nonspecific, although severe and persistent bed bug infestation has been implicated in the development of iron deficiency anemia.²¹

Diagnosis

The appearance of the insect bite does little to assist in identifying the culprit insect; a mosquito bite looks like a flea bite that looks like a bed bug bite.¹⁹ Bites organized in linear or clustered groups of 3 (breakfast, lunch, and dinner) have been suggested as implicating a flea or bed bug, but this is far from diagnostic.

Differential Diagnosis

• ✓ Other arthropod bites: May be indistinguishable from bed bug bites.

• ✓ Urticaria: The individual lesions last less than 24 hours.

• ✓ Delusions of parasitosis: Can present with similar symptoms, but patients with bed bug infestations often struggle with psychopathology secondary to their infestation, so true infestation should be ruled out.

Management

The patient should be treated symptomatically with oral antihistamines and topical corticosteroids and with topical or oral antibiotics if the bites are infected. Once an infestation is established, bed bugs are extremely difficult to treat. The best advice is to prevent a bed bug infestation before it occurs by being proactive and avoid bringing them home. Suggestions include checking hotel rooms before unpacking, especially bed sheets, linens, and mattress seams, avoiding setting luggage on the floor, and checking the luggage rack for signs of bed bugs.¹⁸ Once at home, clothing and luggage should be carefully examined and if infestation is suspected on these items, bed bugs can be destroyed by freezing (minimum of 23°F (−5°C)) maintained at least 5 days (2 weeks if uncertain of temperature) or heating (minimum target is 2-hour core exposure at 120°F (49°C)).¹⁸

Consultation

A dermatologist might be consulted if the diagnosis is in question. Occasionally a mental health care professional might be needed to help with the psychosocial aspects. If a patient's home is truly infested with bed bugs, the most important consultation will be that of a pest management professional.

Patient Information

• JAMA Patient Page: Bed bugs: www.jama.ama-assn.org/-content/301/13/1398.full.pdf

• United States Environmental Protection Agency: www.epa.gov/bedbug

• University of Minnesota Department of Entomology: www.bedbugs.umn.edu