Bug Bites and Infestations

CHAPTER	19
BUG BITES AND INFESTATIONS

Tinea (Dermatophytoses)

Synonyms	Ringworm, athlete’s foot, and jock itch.
Inheritance	n/a
Prenatal Diagnosis	n/a
Incidence	Worldwide. Leading cause of cutaneous fungal infections. Prevalence and species vary with geography, socioeconomic status. Incidence is not clear because of underreporting.
Age at Presentation	Common in young children, especially tinea capitis; tinea pedis, manuum, and cruris are more common after puberty.
Pathogenesis	Dermatophytes infect of keratinocytes of the hair, invade keratinocytes of the hair, follicles, nails, or skin; minor superficial trauma is a common cause in many; rare direct dermal invasion in immunocompromised hosts; transmission from person to person, cat or dog to human, or from contaminated soil or floor or inanimate objects such as combs, brushes, hats, and clothing.
Key Features	Tinea corporis, faciei or barbae Red, scaly papules (sometimes follicular) coalescing into annular scaly plaques, centrifugal spread; rare, pustules, vesicles, and bullae; rare, pink to red plaque with (draining) pustules, thick serous crust (tinea profunda, Majocchi granuloma); regional adenopathy common. Tinea cruris Red, scaly papules, sometimes follicular, coalesce into annular scaly plaques that spread centrifugally; can often be macerated; medial proximal thighs, buttocks, gluteal cleft, pubic area and waist; usually spares the scrotum. Tinea pedis and manuum Macerated scaly patches with erythema in the interdigital web spaces; occasional fissures; dry scaly papule and patches with pink erythema diffusely on the palmoplantar surfaces lateral hands and feet; usually spares weight bearing surfaces; rarely, pustules, vesicles, or bullae.
Differential Diagnosis	Atopic dermatitis, seborrheic dermatitis, alopecia areata, trichotillomania, granuloma annulare, erythema annulare centrifugum, pityriasis rosea, contact dermatitis, subacute cutaneous lupus, and nail lichen planus.
Laboratory Data	Wood’s lamp inspection may fluoresce green (but only with Microsporum or Trichophyton schoenleinii); skin scraping with or without hair for KOH prep; hair, skin scraping, or swabbing the scalp for fungal culture; rarely, skin biopsy; consider test of cure with culture after treatment.
Management	Hair involvement or inflammatory, pustular tinea Griseofulvin microsize: 20 to 25 mg/kg (max 1 g) daily for 8 to 12 weeks or 2 weeks after clinically clear; best option for Microsporum canis; can cause a photosensitivity reaction. Terbinafine: 5 mg/kg/d for 6 weeks; low cost and short course compared with griseofulvin often first-line treatment except for Microsporum tinea capitis (griseofulvin); granules are expensive and rarely available; tablets are on many pharmacy $4 plans and can be cut in half or quarters and crushed to powder and administered with fatty foods. Itraconazole 5 mg/kg/d for 6 weeks; off-label but recommended by CDC and AAP Redbook. Fluconazole 5 to 6 mg/kg/d for 6 weeks; off-label as well but good studies show efficacy for tinea capitis. Tinea corporis or facei Terbinafine 1% and naftifine 1% (allylamines) applied twice daily to the lesion and its surrounding borders for 1 week after clinical resolution. Econazole 1%, miconazole 2%, clotrimazole 1%, and oxiconazole 1% (imidazoles) applied twice daily to the lesion and its surrounding borders for 1 week after clinical resolution. Ciclopirox 1% applied twice daily to the lesion and its surrounding borders for 1 week after clinical resolution. Longstanding or widespread tinea corporis especially if deep-seated rash may be safely treated with 2 to 4 weeks of oral medications described above for tinea capitis.
Prognosis	Good. Some mild cases of tinea corporis resolve spontaneously but most can be treated with topical antifungals. If recurrent, persistent or widespread infection, then oral antifungal therapy for at least a 2 to 4 weeks; an eczematous reaction (“Id reaction”) maybe seen in other areas of the body (eg, sides of fingers) not infected in patients with a vigorous reaction to the dermatophyte infection. These areas can be treated symptomatically with a topical steroid. Infections in immunocompromised hosts can be superficial or invasive and involve multiple species. For sites previously treated with topical steroids, even in combination with antifungals, consider treating as a “partially treated” infection with oral antifungal therapy. Combination therapy with oral or topical steroids and antifungal medications should be avoided to prevent “tinea incognito” that represents a partially treated tinea camouflaged by the steroid, resulting in persistent or recurrent clinical tinea corporis. Nail involvement may involve nondermatophyte species, consider pretreatment culture. Treatment with oral antifungal medications in healthy children for 6 weeks or less usually does not require laboratory monitoring. However, children requiring longer course of therapy or on medications that may interact with oral antifungal agents, consider at least liver function testing.

PEARL/WHAT PARENTS ASK

Good hygiene, especially after exercising, and use of sandals at the pool or public showers/baths. Where did they acquire infection? Most tinea capitis is acquired from close contacts especially siblings and close friends. These individuals should be examined and cultured and treated if suspicious lesions are identified. Older children who participate in sports and activities requiring close contact like wrestling should be monitored by parents because they are high risk for acquiring multiple skin infections. Hair regrowth can take 6 to 12 months. No permanent hair loss unless scarring.

Skin

Associated Findings

Head Lice

Synonym	Pediculosis capitis.
Inheritance	None, acquired.
Prenatal Diagnosis	n/a
Incidence	Uncertain, underreported, few population-based studies; F>M.
Age at Presentation	Most common in school aged children.
Pathogenesis	Direct head-to-head contact with an infected person; saliva from the bite of the louse causes an inflammatory reaction; transmission via inanimate objects (eg, combs and brushes) is probably more common in warmer months.
Key Features	Skin: Pruritus days to weeks after initial infestation, within 48 hours of reinfestation; pink to red papule or linear excoriation on the scalp, especially at the hair lines; nits (eggs) are white to brown and firmly adherent to the hair shaft; live lice often seen on the scalp when parting or brushing the hair.
Differential Diagnosis	Hair casts, black piedra, white piedra, seborrheic dermatitis, atopic dermatitis, and insect bites.
Laboratory Data	None required, clinical diagnosis; nits on hair shafts close to scalp along with adult lice are ideal; nits alone, particularly if >1/4 inch off the scalp, are not diagnostic of an active infestation; Wood’s lamp examination of the hair may fluoresce nits a pale blue; wet combing the entire scalp twice can aid in visualizing nits or adult lice.
Management	Antihistamines or topical steroids as needed for itching. Topical pediculicides Permethrin 1% lotion: Apply to dry scalp and hair, rinse after 10 minutes, repeat in 7 to 9 days, possibly repeat 2 weeks later since not effective against nits; increasing resistance. Malathion 0.5% lotion: Apply to dry scalp and hair, rinse after 8 to 12 hours; ovicidal; malodorous, flammable, and irritating; safety in children under 6 years has not been established. Ivermectin 0.5% lotion: Apply to dry scalp and hair, rinse after 10 minutes; not ovicidal but very effective against nymphs on emergence; emollient effect of olive oil and shea butter vehicle, nonsensitizing and nonirritating; approved for use in children over 6 months of age. Benzyl alcohol 5% lotion: Apply to dry scalp and hair, rinse after 10 minutes; repeat in 7 days; not ovicidal; approved in children over 6 months of age. Spinosad 0.9% cream rinse: Apply to dry hair, rinse 10 minutes later; approved for children over 6 months old, consider a second treatment 1 to 2 weeks later. Ivermectin oral: 200 to 400 mcg/kg (weight >15 kg) single dose, possibly repeated on day 7 to 9. Wet combing: Apply lubricant (eg, hair conditioner) to wet hair and systematically comb (with a fine-toothed comb) all the hair at least twice until no lice identified; repeat every 3 to 4 days for several weeks, efficacy not proven. Lindane 1% shampoo: Not first-line therapy, should be used with caution, high risk of adverse effects; banned in California and some countries, used with caution in children, elderly adults, immunocompromised individuals, patients under 110 pounds.
Prognosis	Good, no immunity so repeat infestation possible, rare risk for impetiginization and cervical lymphadenopathy.

PEARL/WHAT PARENTS ASK

No relationship to hygiene or socioeconomic factors, in fact most common in patients with good hygiene. All household members should be treated at the same time. Lice are unlikely to survive >48 hours off the scalp or after washing clothing or linen in hot water or drying clothing or linen on high heat (≥130 °F). Clothing that cannot be washed should be placed in a plastic bag for 14 days in a warm room (75 °F-85 °F) or in a freezing environment (<32 °F). Rare risk of transmission from furniture or carpeting but should be vacuumed to remove hairs. Combs and brushes should be soaked in rubbing alcohol for 15 minutes and washed in hot water, they can be placed in dish washer. Electric combs, scalp oils, or heated air have not been studied and may risk burns. Do not spray home with pediculicide. Children should not be excluded from school, no nit policies for school do not make sense and not supported by most teacher groups.

Skin

Associated Findings