Scabies

1. Scabies is a highly infectious skin infestation caused by a tiny mite called Sarcoptes scabiei (
2. common in
   1. school-aged children
   2. closed communities (nursing homes and in some Indigenous communities)
3. Pathology
   1. The female mite burrows just beneath the skin in order to lay her eggs. 
   2. She then dies. 
   3. The eggs hatch into tiny mites that spread out over the skin and live for only about 30 days. 
   4. mite antigen, in its excreta, causes a h ypersensitivity rash.

 

Differential diagnoses of classical scabies
Insect bites	Infections	Dermatitis	Immune-mediated
Mosquitos	Folliculitis	Eczema	Papular urticarial
Midges	Impetigo	Contact dermatitis	Bullous pemphigoid
Fleas	Tinea		Pityriasis rosea
Bedbugs	Viral exanthems

Diagnosis:

• Based on typical appearance and distribution of lesions/rash, and presence of burrows.
• Classic burrow: linear intra-epidermal tunnel (short wavy greyish/white threadlike elevations, 2-10 mm).

• Confirm diagnosis by identifying mite, eggs, or faecal matter through:
  • Removing mite with needle tip from burrow.
  • Skin scraping and microscopic examination with KOH.
  • Dermatoscope identification.

Differential Diagnoses:

Insect bites	Infections	Dermatitis	Immune-mediated
Mosquitos	Folliculitis	Eczema	Papular urticarial
Midges	Impetigo	Contact dermatitis	Bullous pemphigoid
Fleas	Tinea		Pityriasis rosea
Bedbugs	Viral exanthems

CLINICAL FEATURES

1. Intense itching (worse with warmth and at night)
2. Erythematous papular rash
3. Usually on hands and wrists
4. Common on male genitalia 
5. Also occurs on elbows, axillae, feet and ankles, nipples of females
6. Genital scabies causing severe pruritus, showing bruising on the upper thighs from intense scratching

6. Typical distribution of the scabies rash

SPREAD

1. The mites are spread from person to person through close personal contact (skin to skin), including sexual contact. 
2. spread through contact with infested clothes or bedding, although this is uncommon. 
3. Sometimes the whole family can get scabies. 
4. The spread is more likely with overcrowding and sexual activity.

TREATMENT

Treatment of typical scabies
Age	Medication	Brand names	Route	Dose and administration	Frequency
First-line treatment
Younger than 2 months of age	Crotamiton	Eurax	Topical	Apply to whole body, wash off after 24 hours	Repeat daily for three days
Older than 2 months of age	Permethrin 5%	Lyclear	Topical	Apply to whole body, wash off after eight hours	Can repeat after 7–14 days if ongoing symptoms
Second-line treatment
Older than 6 months of age	Benzyl benzoate 25%	AscabiolBenzemul	Topical	Dilute to 6.25% for infants 6 months to 2 years of age Dilute to 12.5% for children 2–12 years of ageApply to whole body, wash off after 24 hours		Repeat once after 7–14 days
Third-line treatment
5 years of age or older	Ivermectin	Stromectol	Oral	200 μg/kg Contraindicated if <15 kg, pregnant, or breastfeeding	Repeat once after 7–14 days

1. Permethrin
   1. best applied to clean, cool, dry skin
   2. Apply to entire body from jawline down (including under nails [with a nail brush], in flexures and genitals).
   3. washed off after eight hours. 
   4. All household contacts should be treated at the same time. 
   5. If the first application is thorough, then no repeat dose is required, as permethrin is active against all stages of the parasite’s life cycle. 
   6. If symptoms persist, a repeat application 7–14 days after the first treatment. 
   7. Permethrin is highly effective and generally well tolerated, but success may be hindered by
      1. non-adherence of asymptomatic contacts
      2. inadequate application
      3. incidental washing off of the therapy.

2. Benzyl benzoate 25%
   1. is the second-line topical agent.
   2. commonly causes skin irritation, and should be diluted with water for children and infants
   3. It is applied and then left for 24 hours before being washed off.

3. Ivermectin
   1. macrocyclic lactone antiparasitic derived from fermentation products of the bacterium Streptomyces avermitilis. 
   2. has very broad antiparasitic activity
      1. onchocerciasis (river blindness)
      2. lymphatic filariasis
      3. soil-transmitted helminths.
   3.  active against the scabies mite, but not its eggs, and has a short half-life of 12–56 hours.
   4. Therefore, repeat dosing 7–14 days after the first dose is required to kill newly hatched mites. 
   5. Ivermectin is the only currently available oral agent that is effective against scabies. 
   6. advantage of ivermectin is its oral formulation, increasing the likelihood that household contacts will adhere to treatment. 
   7. Adverse effects
      1. itch, headache, dizziness, and abdominal and joint pain
   8. does not cross the blood–brain barrier in humans.
   9. not recommended for use in
      1. children younger than 5 years of age or weighing less than 15 kg. 
      2. pregnant and breastfeeding women

3. General Measures
   1. Treat the whole family at the same time even if they do not have the itch.
   2. Decontaminate bedding, clothing, and towels used in the previous 4 days:
   3. Wash at 60°C and dry in a hot dryer, dry-clean, or seal in a plastic bag for 72 hours.
   4. Shoes/non-washable items: Seal in plastic bag for at least 3 days.
   5. Mites do not survive more than 72 hours away from human skin.

• Environmental measures for scabies infection
  • role of transmission of scabies other than person-to-person transmission is controversial
  • Scabies mites are highly susceptible to dehydration away from the human host, surviving for only three days.
  • transmission from fomites is uncommon
  • therefore environmental cleaning(hot water laundry washes etc..) for classical scabies is unnecessary, aside from institutional settings

Treatment of associated impetigo

• secondary bacterial infection
  • initial treatment with antibiotics and removal of crusts
  • followed by topical scabies treatment 
  • Flucloxacillin in adults and cephalexin in children (more palatable than flucloxacillin) are the preferred choice of antibiotics in non-remote settings where S. aureus is the most likely pathogen
  • In remote settings, S. pyogenes is the primary driver of infection, and additional treatment options include short-course trimethoprim-sulfamethoxazole or intramuscular benzathine penicillin 

CRUSTED (NORWEGIAN) SCABIES

• Rare
• majority of cases have a relatively small number of mites (as few as 15), infestation with thousands or millions will cause the condition of crusted scabies. 
• places patients at high risk for invasive bacterial infection, sepsis and mortality
• Diagnosis is made on a scraping which reveals vast numbers of lesions.

Treatment usually requires hospital admission for isolation and intensive treatment with a combination of topical scabicides, oral ivermectin and topical keratolytics. 

• Public health considerations
  • Because of the prolonged asymptomatic phase, scabies is often spread from person-to-person before a diagnosis is made
  • scabies outbreak is indicative of transmission within the institution for at least several weeks. 
  • Widespread outbreaks may occur in closed communities, such as hospitals, RACFs and prisons, or areas where overcrowding is common. 
  • patient should be isolated in a single room until 24 hours after the first treatment has been completed, if possible, and staff and visitors should use contact precautions during this period. 
  • The index case should be treated, along with staff or visitors who had direct contact with them.