Pediculosis refers to louse infestation, an ectoparasite that lives on the body. Lice feed on human blood after piercing the skin and injecting saliva, which may cause pruritus due to an allergic reaction.
Pediculosis is endemic in both developing and developed countries.
Girls are at higher risk of head louse infestation than boys. This is not because of hair length but the social behavior (head-to-head contact, sharing of hats etc)
Children of age 3-11 years are most susceptible because of close contact in classrooms and daycare facilities.
P pubis infestation is more common in people aged 14-40 years who are sexually active.
Types of Pediculosis
Different lice species prefer different body parts, it could be classified
- Pediculus capitis (head lice) [most common]
- Pediculus corporis (body lice)
- Pthirus pubis (pubic lice, also called “crabs”).
Pediculus humanus capitis
Head louse infestation is spread by close physical contact and occasionally by shared fomites (eg, combs, brushes, hats, scarves, bedding, clothing, headgear, hats, combs, hairbrushes, hair barrettes, may occasionally play a role in the spread of head lice. Young age, close, crowded living conditions and warm weather are risk factors
Pediculus humanus corporis
The body louse does not live on the human body. Because it prefers cooler temperatures, it primarily lives in human clothing, crawling onto the body only to feed, predominantly at night.
These can spread through the contact with clothing, bedding, or towels of an infested individual, or through direct physical contact.
Crowded living situations and infrequent washing of clothes are risk factors.
The pubic louse is white to gray and oval and is also called crab lice because of shape.
Intimate or sexual contact with an individual who is infested with pubic lice is a common risk factor for pubic lice infestation. Sexual promiscuity and crowded living conditions are risk factors. Contact with clothing, bedding, and towels can cause the infestation.
P pubis infestation is classified as an STD. Upon diagnosis of pubic lice, the concern should be raised about the possibility of concomitant STDs.
The average nit is 0.8 mm long. The nit attaches to the base of the hair shaft or to fibers of clothing (body lice) with a strong, highly insoluble cement and is difficult to remove.
Lice as vectors
Head lice are not vectors for other organisms that cause disease.
- R prowazeki, causes typhus fever
- B quintana – causes trench fever
- B recurrentis – causes relapsing fever.
Often the patient comes to the attention of a health care after discovering lice or nits.
Otherwise, itching is the most common symptom of infestation. Itching may disturb sleep in children.
Light infestations can be asymptomatic.
Areas affected in head louse infestation include the scalp, the back of the neck, and postauricular areas.
Patients infested with P corporis experience nocturnal pruritus, particularly in the axillary, truncal, and groin regions,
A diagnosis of any type of pediculosis rests on the observation of eggs (nits), nymphs, or mature lice. Definitive diagnosis of active infestation requires detection of live lice.
Wetting the hair and using a fine-tooth “bug-busting” comb is useful to dislodge eggs and to remove live lice/nymphs for examination.
Another technique is to fasten a piece of transparent adhesive tape to the infested areas. Lice stick to the tape.
Physical examination may reveal occipital lymphadenopathy in head louse infestation
Physical examination findings in body louse infestation may show include multiple lesions from bites.
Maculae cerulea are blue-gray macules, which are actually a discoloration of the skin due to the insect’s bite and are considered pathognomic.
The diagnosis of body lice depends on the close examination of the patient’s clothing for crawling lice and nits
Body louse infestation is also known as vagabond disease, and individuals who have an infestation for many years can develop a condition termed vagabond skin characterized by thickened and darkened skin after years of bites.
P pubis infestation may spread to the hair around the anus, abdomen, axillae, chest, upper arms, eyebrows, and eyelashes.
Excoriations are common. Inguinal lymphadenopathy and axillary lymphadenopathy have also been reported with pubic louse infestation.
- Dermatophyte infection
- Delusions of parasitosis
- Contact dermatitis
- Conjunctivitis (if eyelash involvement)
Diagnosis of Pediculosis
The diagnosis of infestation requires identification of a live louse and/or a viable nit
For this, cellulose tape can be applied over an infested area to pick up lice and place them on a microscopic slide to be examined.
Wood lamp examination of the infested area shows yellow-green fluorescence of lice and nits.
Patients with P pubis [it is considered a sexually transmitted disease] should be checked for other STDs including HIV, syphilis, and trichomoniasis.
Scrapings for a fungal culture can be checked to rule out dermatophytosis.
Treatment of Pediculosis
Treatment aims to eliminate lice and eggs. Lice killing agents are the mainstay of the treatment. These come in form of medicated lotions or shampoos.
Eyelash infestation can be treated effectively by asphyxiation with petrolatum ointment.
Treatment of pediculosis has 2 aspects: medication and environmental control measures..
In addition, the fomites used by the infested person within 2 days prior to pediculicide treatment be machine washed with hot water and dried with hot air since the lice and eggs are killed. Items that cannot be laundered can be dry-cleaned or sealed in a plastic bag for 2 weeks [cause asphyxiation].
The floors and furniture should be vacuumed in order to remove hairs from an infested individual, which might have been shed with viable nits attached
Environmental measures are more important than drugs in body louse.
The treatment of infested family members, friends, and/or other close contacts at the same time as the infested individual is important in helping to prevent further spread of head lice and in preventing re-infestation. In the case of pubic lice, all sexual partners from within the previous month should be treated
Drugs Used in Pediculosis
Various topical pediculicidal agents are available for the treatment of head and pubic lice.
- Pyrethrin shampoos and permethrin 1%
- kill live lice, but not unhatched eggs
- Second treatment 9 days after the first treatment
- Pyrethrin is derived from chrysanthemums
- Permethrin is a synthetic pyrethroid
- Malathion 0.5%
- More ovicidal than permethrin
- More lethal effect
- Decreased frequency of re-infestation.
- Recommended in patients > 6 years or older.
- Reserved for treatment of individuals where alternative treatment has failed/not tolerated
- Topical ivermectin
- Single-dose, 10-minute application
- Not ovicidal but prevents nymphs from surviving.
- Spinosad 0.9%
- Applied to dry hair as a cream rinse
- left in for 10 minutes, and then shampooed out.
- Derived from soil bacteria
Benzyl alcohol lotion 5%
- Obstruct the respiratory spiracles after forcing lice to keep them open.
- Two applications 1 week apart for 10 minutes
- Weakens the waxy shell of lice
- Causes internal fluid loss and dehydration.
- Repeated in 7-10 days
Treatment of Head Louse Infestation
- Medicated lotions or shampoos
- Bedmates/ contacts with treatment
- Re-treatment after 7-10 days
- Shaving is effective but is usually not necessary
- Launder potential fomites (eg, towels, pillowcases, sheets, hats, toys) in hot water
- Combs and hair brushes can be discarded or soaked for at least 5 minutes in very hot water
Treatment of Pubic Louse Infestation
- Treatment similar to the head louse.
- Eyelashes are treated with occlusive therapies with ophthalmic related petrolatum
- Lindane shampoo causes neurotoxicity and should not be used as a first-line agent;
- Check for other STDs
- Fluorescein dye strips may be used in combination with white petrolatum. The strips are applied to the eyelashes for 3 nights.
Treatment of Body Louse Infestation
- Use of a pediculicide is usually unnecessary
- Treatment of clothing and bed linens includes
- laundering in hot water
- Ironing with a hot iron
- Drying in a hot dryer
- Dry cleaning
- Topical agents can be applied to clothing, especially the seams.
- In cases of heavy pediculosis, treatment of the body with a pediculicide shampoo or lotion may be beneficial
Treatments are highly effective in killing nymphs and mature lice, but less effective in killing eggs.
Treatment failure may occur due to
- Inappropriate treatment
- Failure to treat close contacts
- Resistance to pediculicide
Frequent use of pediculicides may cause persistent itching.