scabies

23 Jul

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.

- Internationally, it approximately affects 200 million people annually and more than 400 million people cumulatively 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]
- Direct contact from skin-to-skin
- Contact with infected objects such as towels, bedding, furniture
- Sexual contact with infected people [4]
Medical Students
- Causative agent: Sarcoptes scabiei var. hominis.
- Three clinical forms:
  - Classic scabies: itchy burrows/rash, typically in finger webs.
  - Nodular scabies: erythematous pruritic nodules, often in the axilla and groin.
  - Crusted scabies (Norwegian): highly contagious, thick hyperkeratotic plaques, often in immunocompromised individuals.
- Lifecycle:
  - Female mite burrows into the stratum corneum to lay eggs.
  - Lifecycle includes eggs → larvae → nymphs → adults.
- Transmission:
  - Classic scabies spreads via ≥10 minutes of skin-to-skin contact.
  - Can also spread through fomites (e.g. clothes, bedding).
- Pathological findings:
  - Mites reside in epidermal and dermal layers.
  - Crusted scabies: plaques on palms, soles, under fingernails.
- Host factors:
  - Nodular scabies represents a hypersensitivity reaction.
  - Crusted scabies more likely in those with immunosuppression, diabetes, HIV, or older age.
  - The host's immune status and spread influence mite burden and severity.
Patients
- Scabies is caused by a tiny mite called Sarcoptes scabiei var. hominis.
- Scabies can appear in three ways:
  - Classic: very itchy, rash with burrows often between the fingers.
  - Nodular: red, itchy lumps in places like the armpits and groin.
  - Crusted (Norwegian): scaly, crusty patches often in people with a weak immune system (e.g. due to age, diabetes, or medications).
- The mite burrows into the top layer of the skin and lays eggs.
- The infection spreads easily through:
  - Direct skin contact (needs about 10 minutes).
  - Sharing clothes, towels, or bedding.
- Crusted scabies can show thickened skin patches, often on the hands, feet, or under nails.
- Itch and rash can be caused by your body's reaction to the mites, especially in nodular scabies.
- People with a weaker immune system are more likely to have a severe form that spreads easily.
- The more the mites spread, the worse the symptoms tend to be. [3]
- 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 [5]
- 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) [6]
- 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]
- 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) [8]
Medical Students
- First-line treatment: Topical scabicides, especially permethrin (preferred over lindane due to neurotoxicity).
- Application:
  - Adults/older children: Apply permethrin or lindane to the entire body, wash off after 8–14 hours.
  - Repeat treatment after 7 days.
  - Infants/young children: Apply permethrin to head and neck, avoid eyes/mouth, ensure coverage of intertriginous areas, nails, and umbilicus.
- Alternative treatment:
  - Ivermectin (oral): indicated for
    Treatment-resistant cases
    Non-adherence to topicals
    Immunocompromised patients (e.g. Norwegian scabies)
- Household management:
  - Treat all close contacts simultaneously.
  - Wash bedding, clothing, and towels in hot water, dry on high heat, or isolate for 72 hours.
- Symptom control:
  - Pruritus: managed with topical corticosteroids or oral antihistamines.
- Complications:
  - Secondary bacterial infection: treat with appropriate antibiotics.
- Follow-up:
  - Symptoms may persist up to 3 weeks post-treatment.
  - Use skin scrapings to confirm eradication in unclear cases.
Patients
- Scabies is treated with skin creams (topical) or oral medicines that kill the mites.
- Permethrin cream is usually the first choice. It's safer than lindane, which can affect the nervous system.
- How to use:
  - For adults and older children: Apply cream to the whole body and wash off after 8 to 14 hours.
  - Repeat after 1 week.
  - For babies and young children: Also apply to head and neck (but avoid eyes and mouth) and don’t miss areas like between fingers, belly button, and nails.
- Other options:
  - Ivermectin tablets: used if creams don’t work, are hard to use, or in people with weak immune systems (e.g. crusted/Norwegian scabies).
- Important: Everyone in close contact (e.g. family) should be treated at the same time.
- Wash clothes, bedding, and towels in hot water and dry using high heat, or put them in a sealed bag for 3 days.
- Itching can continue even after treatment. You can use anti-itch creams or antihistamine tablets to help.
- If the skin gets infected, you may need antibiotics.
- Rashes and itching can take up to 3 weeks to go away. This doesn’t always mean treatment failed.
- In some cases, your doctor might take a skin sample to make sure the mites are gone. [6]
- Blood infections (septicaemia)
- Heart disease
- Kidney problems [1]
- Scabies can be passed between humans and household pets
- Scabies is highly contagious
- Scabies are very easily caught [9,10]
- 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?
- SH:24
- NHS Inform
- British Association of Dermatologists
[1] https://www.who.int/news-room/fact-sheets/detail/scabies#:~:text=Scabies%20is%20found%20in%20every,Recurrent%20infestations%20are%20common
[2] https://www.uptodate.com/contents/scabies-epidemiology-clinical-features-and-diagnoss#H2
[3] https://www.ncbi.nlm.nih.gov/books/NBK544306/
[4] https://www.aad.org/public/diseases/a-z/scabies-causes
[5] https://cks.nice.org.uk/topics/scabies/background-information/risk-factors/
[6] https://www.msdmanuals.com/en-gb/professional/dermatologic-disorders/parasitic-skin-infections/scabies?query=scabies
[7]https://www.cdc.gov/parasites/scabies/diagnosis.html#:~:text=Diagnosis%20of%20a%20scabies%20infestation,or%20fecal%20matter%20(scybala)
[8] https://dermnetnz.org/topics/scabies
[9] https://www.clinicaladvisor.com/home/features/debunking-the-myths-surrounding-scabies/#:~:text=Myth%3A%20Scabies%20is%20highly%20contagious.&text=If%20this%20were%20the%20case,)%2C%20not%20from%20brief%20encounters.
[10] https://www.sciencedirect.com/science/article/abs/pii/S0733863505700589