Scabies

Introduction | Aetiology and Pathophysiology | Clinical Presentation | Diagnosis | Management and Treatment | Prevention | When to Refer | References

Introduction

Scabies is a highly contagious skin infestation caused by the mite Sarcoptes scabiei. The condition is characterised by intense itching, especially at night, and a pimple-like rash. Scabies spreads easily through close physical contact, making it common in crowded environments such as care homes, schools, and among family members. The condition requires treatment to eradicate the mites and prevent spread to others.

Aetiology and Pathophysiology

Scabies is caused by the mite Sarcoptes scabiei, which burrows into the skin to lay eggs, leading to an inflammatory response:

• Transmission: The mites are spread through prolonged skin-to-skin contact with an infested person. Less commonly, scabies can be spread through sharing bedding, clothing, or towels, though the mites do not survive long away from the human body.
• Life Cycle: After mating on the skin surface, the female mite burrows into the epidermis to lay eggs. These eggs hatch into larvae, which then mature into adult mites within 10-14 days, continuing the cycle.
• Immune Response: The intense itching associated with scabies is due to a delayed hypersensitivity reaction to the mites, their eggs, and their faeces.

Clinical Presentation

The classic symptoms of scabies include:

• Itching: Intense itching, especially at night, is the hallmark symptom. Itching may begin several weeks after infestation as the immune system reacts to the mites.
• Burrows: Thin, greyish-white, raised lines on the skin, representing the tunnels created by the mites. These are most commonly found in the webbing between the fingers, on the wrists, elbows, around the waist, and on the genitals.
• Rash: A widespread, pimple-like rash may develop, often with small blisters and scales. The rash can appear on any part of the body but is most commonly seen on the hands, arms, armpits, and around the belt line.
• Nodules: In some cases, itchy nodules may develop, particularly in the genital area or armpits.
• Secondary Infection: Scratching can lead to skin breaks and secondary bacterial infections, such as impetigo.

Diagnosis

The diagnosis of scabies is primarily clinical, based on the characteristic symptoms and examination findings:

• Clinical Examination: The presence of burrows, itching, and the characteristic distribution of the rash are typically sufficient for diagnosis. A history of similar symptoms in close contacts can support the diagnosis.
• Microscopy: A skin scraping taken from a burrow can be examined under a microscope to confirm the presence of mites, eggs, or faecal pellets, though this is not always necessary.
• Dermatoscopy: Dermatoscopy can be used to visualise the mites and their burrows directly on the skin.

Management and Treatment

Treatment of scabies involves the eradication of mites from the affected individual and their close contacts, as well as treating the symptoms:

1. Topical Treatments

• Permethrin 5% Cream: This is the first-line treatment for scabies. The cream should be applied to the entire body from the neck down (including under the nails) and left on for 8-12 hours before washing off. A second application may be needed after 7 days.
• Benzyl Benzoate 25% Lotion: An alternative to permethrin, particularly in cases of resistance. It is applied similarly to permethrin but can be irritating to the skin.
• Malathion 0.5% Lotion: Another alternative, particularly for patients who cannot tolerate permethrin or benzyl benzoate.

2. Oral Treatments

• Ivermectin: Oral ivermectin can be used in cases of crusted scabies, severe infestations, or when topical treatment is not practical. It is typically given as a single dose, with a second dose 7-14 days later.

3. Symptomatic Relief

• Antihistamines: Oral antihistamines can help reduce itching, particularly at night.
• Topical Steroids: Mild topical corticosteroids may be used to reduce inflammation and itching, but should not be used as the primary treatment for scabies.

4. Environmental Control

• Clothing and Bedding: All clothing, bedding, and towels used by the infested person and close contacts should be washed in hot water (at least 60°C) and dried on a hot cycle. Items that cannot be washed should be sealed in plastic bags for at least 72 hours to kill any mites.
• Treating Close Contacts: All household members and close contacts should be treated simultaneously, even if they are asymptomatic, to prevent reinfestation.

Prevention

Preventive measures are essential to control the spread of scabies:

• Avoid Close Contact: Avoiding close physical contact with infested individuals can reduce the risk of transmission.
• Prompt Treatment: Early treatment of infested individuals and their contacts is key to preventing the spread of scabies.
• Environmental Cleaning: Regular cleaning and laundering of clothing, bedding, and towels can help eliminate mites from the environment.

When to Refer

Referral to a specialist may be necessary in the following situations:

• Crusted Scabies: Also known as Norwegian scabies, this is a severe form of scabies with extensive scaling and crusting. It requires prompt and aggressive treatment, often involving both topical and oral therapies.
• Treatment Failure: If there is no improvement after appropriate treatment, referral may be needed to assess for possible misdiagnosis, treatment resistance, or reinfestation.
• Secondary Infection: If secondary bacterial infection is suspected, referral may be necessary for management, including possible antibiotic treatment.
• Immunocompromised Patients: Immunocompromised individuals may present with atypical or severe forms of scabies and may require specialist care.

References

1. British Association of Dermatologists (2024) Guidelines for the Management of Scabies. Available at: https://www.bad.org.uk (Accessed: 26 August 2024).
2. National Institute for Health and Care Excellence (2024) Scabies: Diagnosis and Management. Available at: https://www.nice.org.uk/guidance/ng104 (Accessed: 26 August 2024).
3. British National Formulary (2024) Topical and Systemic Treatments for Scabies. Available at: https://bnf.nice.org.uk/ (Accessed: 26 August 2024).