It is quite common to find infestation by human body lice, especially among children. The human body lice infestation is more common in developing countries where the low hygienic, overcrowding and poor environmental conditions favor the spread of human lice.

What is pediculiasis?

Pediculiasis is infestation of human body by human lice. The nymphs and adults of human lice feed at least once a day to survive exclusively on human blood. There are three types of human lice which cause three distinct types of pediculiasis. The three types of human lice are head lice (Pediculus capitis) which infest mainly hairs of scalp, the body lice (Pediculus humanus) which mainly infects the clothing and crab or pubic lice (Phthirus pubis) which mainly infest the hair of the pubic region (can be transmitted during sexual act).

What is the global problem of pediculiasis?

Even in developed industrial countries pediculiasis affects approximately 1% of elementary school–aged children and in the poor and developing countries the incidence of pediculiasis is much more due to overcrowding and poor living conditions, which helps in spread of pediculiasis.

How pediculiasis is transmitted?

Head lice are transmitted mainly by direct head-to-head contact and less commonly by fomites like shared headgear, grooming implements, bedding etc. (contrary to popular belief). Head lice succumb to death if separated form host (removed from host) in approximately 24 hours. The crab or pubic louse (Phthirus pubis) is transmitted mainly by sexual contact, as these lice mainly infest pubic area and less commonly on hair of the axillae and the face (including beard, mustache and the eyelashes). Body lice are generally acquired by direct contact or by sharing of clothing and bedding. Body lice generally remain on clothing except during feeding and generally dies in approximately 2 days if separated from their host. Body lice mainly infest disaster victims or people who are in close contact with other infested individuals.

Female head lice and pubic lice cement their eggs firmly to hair and female body lice to clothing. From egg a nymph hatches approximately 10 days after laying egg. The empty egg called “nit” may remain affixed to hair or clothing for months thereafter.

What diseases can be transmitted by pediculiasis?

Body lice (Pediculus humanus) can transmit (vectors for the disease causing agents) louse-borne typhus, louse-borne relapsing fever and trench fever. Head lice do not act as a vector of any pathogenic organism.

What are the signs and symptoms of pediculiasis?

Infestations by head lice generally remain asymptomatic. The saliva of lice can produce an intensely irritating maculopapular or urticarial rash in sensitized persons. Pruritus or itching is due to hypersensitivity to the louse's saliva, is generally transient and mild in case of head lice infestation.

Pruritic lesions due to body lice are generally seen around the neckline. Chronic infestations by body lice results in a post-inflammatory hyperpigmentation and thickening of skin known as vagabonds' disease.

The crab or pubic lice may cause severe itching. Crab lice can produce pruritic lesions and blue macules of approximately 3 mm in diameter (maculae ceruleae) at the site of bites. Blepharitis (inflammation of eyelids) is seen if infestation occurs in the eyelashes.

How pediculiasis is diagnosed?

Pediculiasis shoild be suspected if nits are detected on hairs or in clothing. But diagnosis of pediculiasis should be done only after confirming presence of live louse in head, body or pubic area. The presence of nits alone is evidence of former infestation and not of current infestation.

How pediculiasis is treated?

Treatment of pediculiasis is instituted only after discovery of louse in head, body or pubic area. Mechanical removal of lice and their eggs by using a fine-toothed louse or nit comb can be tried at first, but may fail to eliminate infestations.

Treatment of active louse infestations is generally done with a 10-minute application of 1% permethrin or pyrethrins and a second application 10 days later for 10 minutes. Louse that persists after second application are generally resistant to pyrethroids (permethrin or pyrethrins).

Chronic infestations may be treated with 0.5% malathion application for 12 hours. Lindane is also sometimes applied for just 4 min but it is less effective and has higher risk of adverse affects, especially if misused. There have been reports of resistance of head lice to permethrin, malathion, and lindane.

Recent study suggests that there is no requirement of isolation or exclusion of children infested with lice from school (which is frequently done), as it is unjustified and without any basis.

Body lice can be easily eliminated by bathing and also by changing to laundered clothes. Application of topical pediculicides like malathion, permethrin or pyrethrins from head to foot may be necessary for hirsute patients. Louse can be removed from clothes and bedding effectively by heating in clothes dryer at approximately 55°C for 30 minutes or by heat-pressing. Emergency mass delousing of persons and clothing may be required during periods of civil strife and after natural disasters to reduce the risk of transmission of louse-borne typhus, louse-borne relapsing fever and trench fever by body lice.

Infestation of pubic lice is treated with topical pediculicides except for eyelid infestations (phthiriasis palpebrum). Eyelid infestation by pubic lice is generally treated by coating the eyelids with petrolatum for 3 to 4 days with good results.