Body Lice

Lice are blood-sucking insects and specific parasites of human beings. Lice are 1-3 mm long and have three pairs of legs that end in powerful claws. Pubic lice are slightly smaller than head lice and body lice. The female lives for 1-3 months but dies when separated from the host. The female louse lays up to 300 eggs, called nits, during her lifetime. These nits are less than 1 mm in diameter and, when viable are opalescent. The nits hatch 6-10 days after laying, giving rise to nymphs that become adults in 10 days. 3 species of lice have adapted to live on humans:

• Head louse (Pediculus humanus capitis) - see separate article on head lice
• Body louse (Pediculus humanus)
• Crab (or pubic) louse (Pthirus pubis) - see below.

Epidemiology

• There are hundreds of millions of cases of pediculosis worldwide.
• Pediculosis and scabies may coexist in the same individual.
• Body lice are associated with poor socioeconomic conditions, with infestation occurring mainly when clothes are not changed or washed regularly. Therefore homeless populations are predominantly affected.¹
• Pediculosis is usually caused by contact with an infested person.

Presentation

• Patients usually present after discovering lice or nits.
• Many lice infestations are asymptomatic.
• Pruritus is accompanied by excoriations that can become infected secondarily and papules linked to bite reactions.
• Diagnosis is based on seeing eggs (nits), nymphs or mature lice. Observing lice is difficult. Nymphs and mature lice, despite being unable to hop or jump, can move rapidly through dry hair. The use of a magnifying glass assists with diagnosis.
• Mature lice are 3-4 mm long. Nits are much smaller (about 1 mm). The pubic louse is about the same length as the head or body louse but has a wider body.
• Body lice can be found in any area of the body, although they tend to avoid the scalp, except at the margins. Nits are laid in the host's clothing and are not usually not found on the hair as with head lice and pubic lice. Body lice and eggs are found in clothing seams.¹
• Chronic infestation often leads to post-inflammatory pigmentation.¹

Investigations

• Unlike dandruff and hair root sheath casts, nits are cemented to the hair and are difficult to remove.
• Nits are fluorescent under a Woods light.

Management

• Bed linens and clothes must be systematically decontaminated.
• Thorough washing of the body with soap followed by application of pyrethroids (permethrin, phenothrin) or malathion for 8-24 hours.
• Outbreaks require delousing of people with 1% permethrin dusting powder, basic sanitation, and hygiene to assure changes of clean clothing, washing of the body, and sometimes shaving.
• Antibiotics are needed to treat louse-borne infectious diseases.
• Treating clothing with permethrin may prevent infestation.

Complications

• The body louse acts as a vector for trench fever, epidemic typhus and relapsing fever.

Prognosis

• Treatments are very effective in killing nymphs and mature lice but less effective in killing eggs.
• Appropriate therapy produces a cure in more than 90% of cases.

Prevention

• To prevent reinfestation, treat contacts of the patient at the same time as the patient.
• Washing combs and brushes reduces reinfestation.

• The pubic louse (Pthirus pubis) is 'crab' shaped, grey-brown in colour, and about 2 mm in length.² The female lays eggs (smaller than a pinhead) on the hair shaft, near to the body. The eggs hatch after about 7 days. The empty eggshells (nits) are tightly attached to the hair and cannot be brushed off.

Epidemiology

• Common among young adults.²
• Pubic lice are transmitted by close body contact, which can be from sexual contact or from close family contact (e.g. from an infested beard or chest).
• Pubic lice in children may be an indication of sexual abuse.

Presentation

• The diagnosis is based on finding adult lice and/or eggs.
• Itching is worse at night and may not develop for several weeks.
• Pubic lice may be found in any coarse hair, such as moustaches, beards, axillary hair and around the margins of the scalp, as well as pubic hair. In prepubertal children, eyebrows and eyelashes are common sites of infestation.
• Blue macules may be visible at feeding sites.
• Minute dark-brown specks of louse excreta are sometimes seen on the skin and underwear.

Differential Diagnosis

• Seborrhoeic scales, small crusts of scratched dermatitis, and hair casts may look like nits but the can all be brushed off whereas nits are very adherent to hairs.
• Clothing lice and head lice are slightly larger than pubic lice.

Management

• Sexual contacts from the previous 3 months and close family contacts should be examined, and treated if infested. It is recommended that those affected and sexually active should have a full screen of sexually transmitted infections.
• Patients should also be screened for associated sexually transmitted disease and treated as necessary.
• Symptoms respond to a topical parasiticidal preparation. In order to kill those lice emerging from eggs that survived the first application, a second applications of insecticide is used 7 days later.
• Carbaryl (unlicensed for crab lice), permethrin, phenothrin, and malathion are effective treatments for crab lice.³
• An aqueous preparation should be applied, allowed to dry naturally and washed off after 12 hours. A second treatment is needed after 7 days to kill lice emerging from surviving eggs. All surfaces of the body should be treated, including the scalp, neck, ears, and face (paying particular attention to the eyebrows and any beard).³
• A different insecticide should be used if a course of treatment fails.
• Alcoholic lotions are not recommended (cause irritation of excoriated skin and the genitalia).
• Recommended treatment regimes include:⁴
  • Malathion 0.5%: apply to dry hair and wash out after at least 2 hrs but preferably, 12 hours, i.e. overnight. Aqueous malathion lotion is effective for crab lice of the eye lashes (unlicensed use).
  • Permethrin 1% cream rinse: apply to damp hair and wash out after 10 minutes.
  • Phenothrin 0.2%: apply to dry hair and wash out 2 hours later.
  • Carbaryl 0.5 and 1%: apply to dry hair and wash out 12 hours later.
  • Eyelashes should be carefully examined for lice, but not treated unless necessary (with 1% permethrin or vaseline).
  • Removal of lice with forceps or application of vaseline (particularly for eyelash infestation in children) are alternative treatments.
• Treatment of itch: antihistamines are of little help in treating pruritus but an oral sedating antihistamine at night may help with sleeping and so reduce scratching.
• If treatment is ineffective, a different class of insecticide should be used for the second course of treatment. This reduces repeated exposure to the same insecticide and so reduces the development of resistance to the medication.¹
• Carbaryl should be considered only when resistance to all other insecticides is suspected. There are no longer any carbaryl preparations licensed for the treatment of pubic lice available in the UK, and it is now a prescription-only medicine because of reports of carcinogenicity in rodents after continuous dosing.

Prevention

• Shaving the infested areas does not provide protection from re-infestation, because pubic lice need only a minimal length of hair on which to lay eggs.