Lice (Pediculosis)

Introduction | Aetiology and Types of Lice | Clinical Presentation | Diagnosis | Management and Treatment | Prevention | When to Refer | References

Introduction

Lice, also known as pediculosis, are parasitic insects that infest human hair and skin, causing itching and discomfort. There are three main types of lice that infest humans: head lice, body lice, and pubic lice. Lice infestations are common worldwide and can affect people of all ages, though children are particularly susceptible to head lice. Lice do not transmit diseases in most cases, but they can cause significant irritation and secondary infections due to scratching.

Aetiology and Types of Lice

Different species of lice infest different parts of the body, each with distinct characteristics and modes of transmission:

• Head Lice (Pediculus humanus capitis): Head lice infest the scalp and hair. They are most commonly spread through direct head-to-head contact, which is why infestations are prevalent in school-aged children. Head lice are not related to poor hygiene.
• Body Lice (Pediculus humanus corporis): Body lice live and lay eggs in clothing and only move to the skin to feed. Infestations are more common in people with poor hygiene or those living in crowded, unsanitary conditions. Body lice can transmit diseases such as typhus and relapsing fever.
• Pubic Lice (Pthirus pubis): Also known as "crab" lice due to their shape, pubic lice infest the coarse hair of the pubic region but can also be found in other body hair, including the chest, armpits, and eyelashes. They are typically spread through sexual contact.

Clinical Presentation

The clinical presentation of lice infestations varies depending on the type of lice but generally includes the following symptoms:

• Itching: The most common symptom of lice infestation is intense itching caused by an allergic reaction to louse saliva. Itching is usually most severe at night.
• Visible Lice and Nits: Lice or their eggs (nits) may be visible on the hair shafts, clothing seams, or in the pubic region. Nits are small, oval, and attached firmly to the hair shaft close to the scalp or skin.
• Red Bumps or Sores: Scratching may cause red bumps or sores on the scalp, neck, shoulders, or other affected areas. These can become secondarily infected with bacteria, leading to impetigo.
• Tickling Sensation: Some patients report a feeling of something moving in their hair, which can be particularly distressing.
• Lymphadenopathy: In severe infestations, regional lymph nodes may become swollen due to secondary bacterial infection.

Diagnosis

The diagnosis of lice infestation is typically clinical, based on the identification of live lice or nits:

• Visual Inspection: Careful examination of the scalp, hair, clothing seams, or pubic hair for live lice or nits is the primary method of diagnosis. A fine-toothed louse comb can be used to aid in detection.
• Microscopic Examination: In uncertain cases, lice or nits can be collected and examined under a microscope to confirm the diagnosis.
• Wood’s Lamp: Nits fluoresce under a Wood’s lamp, which can help in their identification during examination.

Management and Treatment

Treatment of lice infestations involves physical removal of lice and nits, the use of topical insecticides, and addressing the environment to prevent reinfestation:

1. Physical Removal

• Wet Combing: For head lice, wet combing with a fine-toothed louse comb is an effective method. Hair should be wet and conditioner applied to make combing easier. Combing should be done every few days for at least two weeks to remove lice and nits.

2. Topical Treatments

• Permethrin 1% Cream Rinse: Permethrin is the first-line treatment for head lice and pubic lice. It is applied to damp hair, left on for 10 minutes, and then rinsed off. A second treatment may be necessary after 7-10 days to kill newly hatched lice.
• Malathion 0.5% Lotion: Malathion is an alternative treatment for head lice, especially in cases of resistance to permethrin. It should be applied to dry hair and left on for 8-12 hours before washing out.
• Dimeticone 4% Lotion: Dimeticone is a silicone-based treatment that works by physically coating and suffocating the lice. It is a good option for patients who prefer a non-chemical treatment.

3. Environmental Control

• Washing and Cleaning: Clothing, bedding, and towels should be washed in hot water (at least 60°C) and dried on a hot cycle to kill lice and nits. Items that cannot be washed should be sealed in plastic bags for at least two weeks.
• Vacuuming: Vacuuming carpets, upholstered furniture, and car seats can help remove stray lice or nits from the environment.
• Avoiding Shared Items: Patients should avoid sharing combs, brushes, hats, and other personal items to prevent the spread of lice.

Prevention

Preventive measures can help reduce the risk of lice infestation and prevent reinfestation:

• Avoid Head-to-Head Contact: Children and adults should avoid head-to-head contact during play, sports, and other activities.
• Regular Hair Checks: Regular checks of children’s hair for lice and nits can help detect infestations early and prevent them from spreading.
• Educating Patients: Educating patients about how lice are spread and how to prevent reinfestation is important, particularly in households with multiple members.

When to Refer

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

• Persistent Infestation: If lice infestation persists despite appropriate treatment, referral to a dermatologist may be necessary for further evaluation and management.
• Secondary Infection: Referral may be required if there are signs of secondary bacterial infection, such as impetigo, which may need antibiotic treatment.
• Multiple Treatment Failures: If over-the-counter and prescription treatments fail, a specialist may recommend alternative treatments or evaluate for potential resistance.

References

1. British Association of Dermatologists (2024) Guidelines for the Management of Head Lice. Available at: https://www.bad.org.uk (Accessed: 26 August 2024).
2. National Institute for Health and Care Excellence (2024) Lice: Diagnosis and Treatment. Available at: https://www.nice.org.uk/guidance/ng102 (Accessed: 26 August 2024).
3. British National Formulary (2024) Topical Treatments for Lice. Available at: https://bnf.nice.org.uk/ (Accessed: 26 August 2024).