scabies

Scabies is a condition that affects the skin, causing burrows and spots. These are formed from mites laying eggs in the layers of the skin. It causes intense itching and can be spread through bedding/clothing.

Epidemiology

Internationally, it approximately affects 200 million people annually and more than 400 million people cumulatively (measurement is calculated by adding previous years with addition to the current year) every year.
Most common in any poor-resource tropical environments, most likely to affect children and older people. With a 5-50% range in prevalence amongst children [1]
One review from a population-based study found that prevalence ranged from 0.2-71% with the highest found in the Pacific region and Latin America (excluding North America in the study) [2]

Source: DermNetNZ.org

Scabies
Multiple scabies seen on the palms

Source: DermNetNZ.org

Scabies
Scaling from scabies seen in the first web of the hand

Pathophysiology [3]

Medical students
- The mite that causes scabies is Sarcoptes scabiei var. Hominis
- Clinically, it presents in three forms:
  - Classic
  - Nodular
  - Contagious crusted variant also called Norwegian scabies.
- The mites resides in the dermal and epidermal layers of humans as well as animals.
- The infestation begins with the female mite burrowing within the stratum corneum of its host where it lays its eggs. It later develops into larvae, nymphs, and adults.
- It typically takes ten minutes of skin-to-skin contact for mites to transmit to another human host, in cases of classic scabies. Transmission of the disease can also occur by fomite transmission via clothing or bed sheets.
- This presentation of scabies often manifests with hyperkeratotic plaques that can be diffuse or localized to the palms, soles, and under fingernails.
- The nodular form of scabies is a variant of the classic form. This form presents with erythematous nodules with a predilection towards the axilla and groin.
- The nodules are pruritic and considered to be a hypersensitivity reaction to the female mite.
- Crusted scabies occurs in patients who are immunocompromised due to immunosuppressive therapy, diabetes, human immunodeficiency virus (HIV), or older age
- This high density requires only short contact with patients and contaminated materials for infection to occur.
- The immunological condition of the host and the extent of spread usually determines the number of infesting mites
Patients
- The mite that causes scabies is Sarcoptes scabiei var. Hominis
- Clinically, it presents in three forms:
  - Classic- itchy spotty rash usually found between the fingers
  - Nodular
  - Contagious crusted variant also called Norwegian scabies- with scaling and crusts
- The mites resides in between the layers of the skin (dermal and epidermal layers).
- The infestation begins with the female mite burrowing within the stratum corneum (the outermost layers of the skin) of its host where it lays its eggs. It later develops into larvae, nymphs, and adults.
- It typically takes ten minutes of skin-to-skin contact for mites to transmit to another human host, in cases of classic scabies. Transmission of the disease can also occur by fomite (through inanimate objects) transmission via clothing or bed sheets.
- This presentation of scabies often manifests with hyperkeratotic plaques (excessive keratin patches) that can be diffuse (widespread) or localised (specific areas) to the palms, soles, and under fingernails.
- The nodular form of scabies is a variant of the classic form. This form presents with red nodules with the most usually found sites being the underarm and groin.
- The nodules are itchy and considered to be a hypersensitivity (excessive) reaction to the female mite.
- Crusted scabies occurs in patients who have weakened immune systems due to immunosuppressive (suppresses the immune response) therapy, diabetes, human immunodeficiency virus (HIV), or older age
- This high density requires only short contact with patients and contaminated materials for infection to occur.
- The immunological (the state of the immune response in the body) condition of the host and the extent of spread usually determines the number of infesting mites

Scabies

Track seen on the skin formed from scabies, known as burrows

Causes [4]
- Direct contact from skin-to-skin
- Contact with infected objects such as towels, bedding, furniture
- Sexual contact with infected people

Risk factors [5]

Close contact with an infected person
Lower economic status and higher social deprivation
Crowded living spaces such as prison, care homes and nursing homes
Seasonal changes- colder seasons increase survivability of mites

Presentation [6]
- Intense itching as a primary symptom
- Red spots appear on the finger webs, wrist, elbow, armpits, belt line and lower buttocks
- Burrow lines which are brown, wavy lines
- In darker skin, granulomatous nodules (immune cell clump together and form raised spots)

Scabies

Red, crusting and scaling patches on a patient’s hand

Investigations
- Clinical examination based on the appearance of the burrow lines
- Removal of the skin may be necessary to examine whether the scraping has a mite or their eggs in it
  - A painless procedure which requires the tip of a needle. In an infected person, less than 10-15 mites can be found in the sample taken [4,7]

Differential diagnosis [8]
- Bullous (blistering) skin conditions
- Dermatitis- skin inflammation
- Folliculitis- follicle inflammation
- Papular urticaria- spot itchiness
- Prurigo- itchiness of spots
- Psoriasis- skin disorder causing flaky skin
- Acropustulosis- itchy areas of the skin seen in young children (infants)

Scabies

Excoriations (scratched areas of skin) that is due to itching, caused be long term scabies infection

Management [6]

Medical students
- Primary treatment for scabies involves topical or oral scabicides.
  - Permethrin is the first-line topical drug, preferred over lindane due to its neurotoxicity.
  - For older children and adults, permethrin or lindane should be applied to the entire body and washed off after 8 to 14 hours. Treatments should be repeated in 7 days.
  - For infants and young children, permethrin should be applied to the head and neck, avoiding certain areas. Special attention to intertriginous areas, such as the nails, and umbilicus
  - Spinosad 0.9% topical suspension is suitable for adults and children 4 years and older, applied to the entire body for 6 hours before showering. Repeat treatment after 1 week..
- Ivermectin is indicated for:
  - Non-responsive cases
  - Inability to adhere to topical treatment
  - Immunocompromised patients with Norwegian scabies.
- Close contacts should be treated simultaneously, and personal items should be washed in hot water and dried in a hot dryer or isolated.
- Pruritus can be treated with corticosteroid ointments and/or oral antihistamines.
- Secondary infection should be considered and treated with appropriate antibiotics if necessary.
- Symptoms and lesions may take up to 3 weeks to resolve despite killing the mites, making failed treatment difficult to recognize. Periodic skin scrapings can be done to check for persistent scabies.
Patients
- Primary treatment for scabies involves topical (applied to skin) or oral scabicides (drugs to destroy scabies)
  - Permethrin (insecticide) is the first-line topical drug, preferred over lindane (another insecticide) due to its neurotoxicity ( toxic substances that alters the functioning of the nervous system)
  - For older children and adults, permethrin or lindane should be applied to the entire body and washed off after 8 to 14 hours. Treatments should be repeated in 7 days.
  - For infants and young children, permethrin should be applied to the head and neck, avoiding certain areas. Special attention to intertriginous (where two skin areas of the skin rub together) such as nails, and the bellybutton
  - Spinosad 0.9% topical suspension (liquid for skin application) is suitable for adults and children 4 years and older, applied to the entire body for 6 hours before showering. Repeat treatment after 1 week..
- Ivermectin is indicated for:
  - Non-responsive cases
  - Inability to adhere to topical treatment
  - People with weakened immune systems with Norwegian scabies.
- Close contacts should be treated simultaneously, and personal items should be washed in hot water and dried in a hot dryer or isolated.
- Itchiness can be treated with corticosteroid ointments (steroids with an oily consistency) and/or oral antihistamines.
- Secondary infection should be considered and treated with appropriate antibiotics if necessary.
- Symptoms and lesions may take up to 3 weeks to resolve despite killing the mites, making failed treatment difficult to recognize. Periodic (during regular but spaced times) skin scrapings can be done to check for persistent scabies.

Complications [1]
- Blood infections (septicaemia)
- Heart disease
- Kidney problems

Source: DermNetNZ.org

Scabies
Papular (spots) on the 4th interdigital (between fingers) on the hand

Myths
- Scabies can be passed between humans and household pets
- Scabies is highly contagious
- Scabies are very easily caught [9,10]

Questions to ask your doctor
- How did I get scabies?
- How do I prevent spreading scabies to others?
- How long can scabies mites live?
- How long will treatment take before it become effective?
- How can I remove/clean scabies infected furniture to prevent further transmission?
- Should I treat myself if I come into contact with an infected person?