Parasitic Skin Infections

Scabies is an infestation caused by the mite Sarcoptes scabiei. It can affect any part of the body and is transmitted through skin-to-skin contact. It can also be acquired from bedding and clothing.

Definitions

• Scar: A change in the skin secondary to trauma or inflammation. Sites may appear erythematous, hypopigmented, or hypertrophic based on their age or character.
• Pruritus: A sensation that prompts the desire to scratch. Pruritus is often the predominant symptom of inflammatory skin diseases (e.g., atopic dermatitis, allergic contact dermatitis).
• Hyperkeratosis: Increased keratin proliferation leading to skin thickening, such as on the soles of the feet.
• Hyperpigmentation: An increase in the color of the skin.
• Hypopigmentation: Decreased skin pigmentation.
• Depigmentation: Total loss of skin color due to the complete absence of melanocytes.

Clinical Features

• Mites Burrowing and Offspring:

Mites burrow into the skin where they lay eggs. The resulting offspring crawl out onto the skin and create new burrows.

• Hypersensitivity Reaction:

The absorption of mite excrement into skin capillaries triggers a hypersensitivity reaction. The main symptom, which may take four to six weeks to develop, is generalized itch, especially at night.

• Silvery Lines:

Characteristic silvery lines may be visible in the skin where mites have burrowed.

• Classic Sites:

Classic sites for scabies infestation include the interdigital folds, wrists, elbows, umbilical area, genital area, and feet.

Diagnosis

• Typical Clinical Appearance:

The clinical appearance is usually typical, but there is often diagnostic confusion with other itching conditions such as eczema.

• Microscopic Examination:

Scrapings taken from burrows may be examined under light microscopy to reveal mites.

Management

• Education and Treatment Guidance:

Parents should receive a detailed explanation of the condition and clear, accurate written information on how to apply the treatment.

• Treatment for Close Contacts:

Treat everyone in the household or in close contact at the same time. Disregard pleas from those who do not itch, as infected individuals can be asymptomatic and still spread the infestation.

• Hygiene and Bedding:

Change bedding, nightclothes, and towels on the night of treatment, and clean them in a hot wash and iron them afterward.

• Possible Complications:

Complications of treated or wrongly treated scabies can include:

• Secondary bacterial infection
• Pyoderma, cellulitis, lymphadenitis
• Septicemia, glomerulonephritis
• Eczematisation
• Acarophobia (a delusion that the infestation persists despite successful treatment)

Treatment

• Treat Together:

All children and affected family or group members should be treated together, preferably at night.

• Scrub and Apply Scabicide:

Scrub thoroughly with soap and sponge. Then, apply scabicide (benzyl benzoate emulsion 25%) firmly into the skin from the neck to the toes.

• Repeat Treatment:

Repeat the procedure on two or three consecutive nights. Repeat the course of treatment after one week to target newly hatched young mites.

• Permethrin 5% Cream:

Applied to all areas of the body from the neck down. Wash off 8-12 hours after application. Adverse events are very low.

• Lindane (γ Benzene Hexachloride) 1% Lotion or Cream:

Applied thinly to all areas of the body from the neck down. Wash off thoroughly after 8 hours.

• Malathion:

Specific instructions for the use of Malathion are not provided here. Please refer to medical guidance for proper usage.

• Crotamiton 10% Cream:

Applied thinly to the entire body from the neck down, nightly for 2 consecutive nights. Wash off 24 hours after the second application.

• Sulfur 2-10% in Petrolatum:

Apply to the skin for 2-3 days.

• Systemic Ivermectin:

Ivermectin, 200 μg/kg PO (single dose) reported to be very effective for both common and crusted scabies in 15-30 days.

Aetiology

• Ancylostoma braziliense: Most common cause in central and south eastern United States.
• Other Hookworms: Includes A. caninum, Uncinaria stenocephala (hookworm of European dogs), Bunostomum phlebotomum (hookworm of cattle).
• Ova Deposition and Larval Penetration: Ova of hookworms are deposited in sand and soil in warm, shady areas, hatching into larvae that penetrate human skin.
• Risk Factors: Activities and occupations that pose risk include contact with sand/soil contaminated with animal feces: playing in sandbox, walking barefoot or sitting on the beach, working in crawl spaces under houses, etc.
• Larval Viability: Larvae remain viable in soil/sand for several weeks.
• Migration and Inflammatory Reaction: Larvae penetrate human skin and migrate within the epidermis up to several centimeters a day. The parasite induces a localized eosinophilic inflammatory reaction with edema and vesicle formation.
• Larval Fate: Most larvae are unable to develop further or invade deeper tissues and die after days or months.
• Incubation Period: 1 – 6 days from the time of exposure to the onset of symptoms.

Clinical Features

• Local Pruritus: Begins within hours after larval penetration.
• Lesion Characteristics: Serpiginous, thin, linear, raised, tunnel-like lesion 2 – 3mm wide containing serous fluid.
• Lesion Multiplicity: Several or many lesions may be present, depending on the number of penetrating larvae.
• Lesion Distribution: Exposed sites, most commonly the feet, lower legs, buttocks, and hands.

Course

• Self-limited: Humans are "dead end" hosts.
• Lesion Resolution: Most larvae die and the lesions resolve within 2 – 8 weeks; rarely, up to 2 years.

Symptomatic Therapy

• Topical Glucocorticoid: Apply a glucocorticoid preparation topically under occlusion to the lesion.

Anthelmintic Agents - Topical

• Effective Topical Agents: Thiabendazole, ivermectin, albendazole.

Anthelmintic Agents - Systemic

• Thiabendazole: Orally, 50 mg/kg per day in two doses (maximum 3 g/d) for 2 - 5 days.
• Ivermectin: 6 mg twice daily.
• Albendazole: 400 mg/d for 3 days; highly effective.

Other Treatments

• Cryosurgery with Liquid Nitrogen: Apply to the advancing end of the larval burrow.
• Removal of Parasite: Do not attempt to extract; parasites are not in visible lesions.

Lice Characteristics: Lice are flat, wingless, blood-sucking insects. Their eggs (nits) are laid on hairs or clothing.

Types of Lice:

• Body or Clothing Lice (Pediculus humanus corporis)
• Head Lice (Pediculus humanus capitis)
• Pubic or Crab Lice (Phthirus pubis)

Ova (Nits) Attachment: The ova or nits are glued to hairs or fibers of clothing but not directly on the body.

Lifecycle and Feeding:

• Larvae Survival: Freshly hatched larvae die unless a meal is obtained within approximately 24 hours and every few days thereafter.
• Feeding Behavior: Both nymphs and adult lice feed on human blood, injecting their salivary juices into the host and depositing their fecal matter on the skin.

Symptoms and Sensitization:

Symptoms of infestation do not appear immediately but develop as an individual becomes sensitized. The hallmark of all types of pediculosis is pruritus.

Pediculosis Corporis

• Rare in Children: Pediculosis corporis is rare in children except under conditions of poor hygiene.
• Transmission: The parasite is transmitted mainly on contaminated clothing or bedding.
• Primary Lesion: Intensely pruritic small red macule or papule with a central hemorrhagic punctum located on the shoulders, trunk, or buttocks.
• Additional Lesions: Excoriations, wheals, and eczematous, secondarily infected plaques.
• Therapy: Improved hygiene and hot water laundering of all infested clothing and bedding.

Pediculosis Capitis

• Transmission: Head to head contact is the most important mode of transmission. Shared combs, brushes, or towels have a more important role in louse transmission.
• Pyodermas: Head lice are a major cause of numerous pyodermas of the scalp, particularly in tropical environments.
• Treatment:
• Permethrin 1% Cream Rinse (Nix): Applied for 10 minutes with a repeat application in 7 – 10 days.
• Malathion: Kills all lice after 5 minutes of exposure and >95% of eggs fail to hatch after 10 minutes of exposure.
• Pyrethrin
• Lindane

Pediculosis Pubis

• Transmission: Transmitted by skin to skin or sexual contact with an infested individual; the chance of acquiring the lice by one sexual exposure is approximately 95%.
• Demographics: The infestation is usually encountered in adolescents, although small children may occasionally acquire pubic lice on the eyelashes.
• Symptoms: Patients experience moderate to severe pruritus and may develop a secondary pyoderma from scratching.
• Treatment: Pyrethrin and lindane cream.