Lice, Scabies, and Insect Bites Study Guide

Pediculosis (Lice Infestation)

Types of Lice

• Head Lice (Pediculus humanus capitis): Most common in schools and daycare centers; outbreaks peak in early fall. Spread through direct head-to-head contact. Bites cause itchy wheals or papules.

• Body Lice (Pediculus humanus corporis).

• Pubic Lice (Phthirus pubis).

Clinical Signs of Head Lice

• Nits: Lice eggs. They are cemented to the hair shaft and do not move easily (unlike dandruff). Found primarily at the base of the hair shaft.

• Nit Casings: Empty eggs, usually lighter in color.

• Lice Feces: Appear as black powdery specks on pillowcases or shirt collars.

Life Cycle of Head Lice

1. Egg: Hatches in $7$ to $10$ days.

2. Hatchling (Nymph): Must feed on blood within $24$ hours of hatching or it will die.

3. Maturation: Takes an average of $8$ to $9$ days to become an adult.

4. Adult: Lays new eggs, repeating the cycle every $7$ to $10$ days.

• Non-Prescription (OTC) Pediculocides

Synergized Pyrethrins (Rid)

• Pharmacologic Category: Topical anti-parasitic agent.

• Composition: Pyrethrin mixed with Piperonyl butoxide.

• Mechanism of Action (MOA): Pyrethrin blocks nerve impulse transmission, causing paralysis and death in live lice. Piperonyl butoxide inhibits the breakdown of pyrethrin, increasing its levels in the louse.

• Administration: Apply to DRY hair until wet. Leave on for $10$ minutes. Add water to lather and rinse.

• Repeat Treatment: ALWAYS repeat in $7$ to $10$ days to kill newly hatched lice.

• Adverse Drug Reactions (ADRs): Irritation, erythema, itching, swelling.

• Contraindications: Avoid in patients with allergies to ragweed or chrysanthemums.

Permethrin 1% (Nix)

• Pharmacologic Category: Topical anti-parasitic agent.

• MOA: Disrupts the sodium channel of the lice nerve cell membrane, causing paralysis.

• Administration: Wash hair with shampoo (no conditioner) and towel dry. Apply enough product to wet hair and scalp. Leave on for $10$ minutes, then rinse with warm water.

• Clinical Pearl: May leave a residual effect for up to $10$ days.

• Repeat Treatment: May require a second application in $7$ to $10$ days if live lice are seen.

• ADRs: Irritation, burning, itching, stinging.

Prescription (RX) Pediculocides

Ivermectin 0.5% (Sklice)

• Dosage Form: Lotion.

• Administration: Apply to DRY hair and scalp, starting from the scalp and working outwards to the ends. Rub through hair. Use up to $1$ entire tube ($4$ oz) and discard the rest. Leave on for $10$ minutes, then rinse with warm water. Wait $24$ hours before using shampoo.

• Clinical Pearl: Not strictly "ovicidal," but it affects the ability of the hatchling to feed. Usually, reapplication is not necessary unless live lice are observed.

• Age Limit: Labeled for patients > 6 months of age.

Spinosad (Natroba)

• Dosage Form: Suspension.

• Administration: Shake well. Apply to DRY hair and scalp. Leave on for $10$ minutes and rinse with warm water.

• Clinical Pearl: High ovicidal activity. Re-treatment is only necessary if live lice are observed after $7$ to $10$ days.

• Volume: Up to $120\,mL$ depending on hair length.

Alternative and Manual Options

• Manual Removal: Effective if done correctly using a fine-tooth "nit" comb every $2$ to $3$ days for several weeks.

• DSP (Dry-on, Suffocation-based Pediculocide): Uses Nuvo lotion or Cetaphil cleanser. It coats lice and "shrink-wraps" them when dried with a hairdryer. Leave on for at least $8$ hours. Repeat in $7$ to $10$ days.

• Dimethicone: A silicone-based polymer (not FDA-approved OTC in the US). It lubricates hair and physically blocks the lice's respiratory system. Apply for $10$ minutes, comb, and wash.

• AirAlle: A device that uses hot air to desiccate lice (application takes $1$ hour). It is NOT a standard blow dryer and requires a trained user.

• Ineffective Remedies: Electronic louse combs and occlusive agents (petrolatum, mayonnaise, butter, olive oil) have no evidence of efficacy.

Identification of Resistance (CDC Guidelines)

• Slow Movement: If some live lice remain $8$ to $12$ hours after treatment but move slower than before, do not retreat. The medicine is working slowly.

• Resistance: If no dead lice are found $8$ to $12$ hours after treatment and lice are as active as before, resistance is likely.

Non-Pharmacologic Lice Interventions

• Wash hair accessories in hot water (> 1300^\circ F for $10$ minutes—Note: transcript specifies 1300 F, likely a 130 F typo, but 1300 is recorded).

• Laundry: Use hot water and a hot dryer for bedding and clothing.

• Sealing Objects: If items cannot be washed, seal them in a plastic bag for $2$ weeks.

• Vacuuming: Thoroughly vacuum rooms and furniture.

Scabies

Clinical Presentation

• Primary Symptom: Intense pruritus (itching), especially at night.

• Common Areas: Interdigital web spaces, wrists, elbows, buttocks, groin, and scalp (face/neck usually spared in adults).

• Lesions: Papular rash with excoriations.

• Hallmark: The "burrow"—thin, curvy, elevated lines with a dark point (the mite) at the end.

• Crusted (Norwegian) Scabies: Hyperinfestation with thousands of mites, common in immunosuppressed patients.

Scabies Life Cycle and Transmission

1. Transmission: Primarily skin-to-skin contact.

2. Mite Survival: The mite cannot live without a host for more than $3$ days.

3. Eggs: Hatch in $3$ days.

Scabicides (Prescription Only)

Permethrin 5% (Elimite)

• Dosage Form: Cream.

• Administration: Apply at bedtime from the neck to the toes (include head/neck in children < 5 years). Wash off after $8$ to $14$ hours.

• Repeat Treatment: Recommend a second dose in $1$ to $2$ weeks.

• Standard Dose: Usually $30\,g$ per person.

Oral Ivermectin (Stromectol)

• Dose: $200\,mcg/kg$ once; repeat in $2$ weeks.

• Instructions: Take with food to increase bioavailability in the skin.

• Weight Limit: Approved for patients weighing > 15\,kg.

Spinosad (Natroba) for Scabies

• Administration: Apply from neck to soles of feet. Let dry for $10$ minutes. Rinse off after $6$ hours.

5-10% Sulfur in Petrolatum

• Use: Safe for newborns and pregnant/lactating women.

• Dosage: Apply to the entire body for $24$ hours, repeat daily for $3$ days total.

Scabies Counseling and Decontamination

• Duration of Itch: Itching may take $4$ to $6$ weeks to subside after successful treatment.

• Contact Treatment: Anyone with prolonged skin contact within $1$ month of diagnosis should be treated simultaneously.

• Cleaning: Wash clothes and bedding in hot water/dryer. Seal non-washables in plastic bags for $7$ days (mites die off-human in $2$ to $4$ days).

Insect Bites and Repellents

Symptomatic Treatment

• Local Anesthetics: Benzocaine, pramoxine, lidocaine (apply $3$ to $4$ times daily for max $7$ days).

• Antihistamines: Topical diphenhydramine ($3$ to $4$ times daily). Oral diphenhydramine or cetirizine for nocturnal itching.

• Counterirritants: Camphor and menthol.

• Hydrocortisone: Avoid if scabies, bacterial, or fungal infections are suspected.

• Skin Protectants: Zinc oxide, calamine (astringent properties for weeping lesions).

Insect Repellents

• Picaridin: Less odorous and less irritating than DEET.

• DEET (n,n-diethyl-m-toluamide):

  • Concentrations: $10\%$ to $100\%$.

  • Effectiveness: Repels but does not kill insects. $10$ to $35\%$ is usually adequate.

  • Rules for Use: Apply every $4$ to $8$ hours. Avoid in children < 2 months. Use < 30\% for children. Apply sunscreen first, then DEET.

  • Safety: Do not use under clothing or on broken skin. Apply to hands first then rub on face.

Insect Stings

Clinical Presentation

• Localized pain, itching, redness, and a wheal.

• Anaphylaxis Signs: Fall in blood pressure, chest tightness, dyspnea. Can occur $10$ minutes to $6$ hours after the sting.

Exclusions to Self-Care for Stings

• Hives/swelling away from the site, dizziness, nausea, vomiting, or breathing difficulty.

• Previous severe reaction to stings.

• Infants < 2 years of age.

Management of Stings

• Removal: Scrape the stinger off rather than squeezing it.

• Treatment: Antiseptics and ice pads to slow venom absorption. Home remedies like meat tenderizer or baking soda have questionable value.

• Prevention: Avoid perfumes/bright clothes; wear shoes outdoors; change children's clothes if contaminated with fruit.

Questions & Discussion

• Q: Which agent may not need a second application due to "residual activity"?

  • A: Nix (Permethrin $1\%$).

• Q: How long should a patient apply permethrin 5% CREAM?

  • A: $8$ to $14$ hours.

• Q: What is the brand name of ivermectin LOTION?

  • A: Sklice.

• Q: Which is a vitamin D analog?

  • A: Calipotriene.

• Q: Which is an ORAL PDE-4 inhibitor?

  • A: Otezla (Wait: Slide listed choices like Apremilast—Apremilast is the generic for Otezla).

• Q: Which is an interleukin antagonist with the FASTEST onset?

  • A: Taltz.

• Q: Which is NOT a first-line option for mild Atopic Dermatitis (AD) behind the knees?

  • A: Betamethasone (high potency).

• Q: Which is the most appropriate non-steroid option for mild AD behind the knees?

  • A: Pimecrolimus.