Clinical Features:
The majority of infestations are asymptomatic.  When symptoms are noted they may include a tickling feeling of something moving in the hair, itching, caused by the an allergic reaction to louse saliva, and irritability.  Secondary bacterial infection may be a complication.

Modes of Transmission:
The main mode of transmission is contact with a person who is already infested (i.e., head-to-head contact).  Contact is common during play (sports activities, playgrounds, at camp, and slumber parties) at school and at home.

Less commonly, transmission via fomites may occur.  Wearing clothing, such as hats, scarves, coats, sports uniforms, or hair ribbons worn by an infested person; using infested combs, brushes or towels; or lying on a bed, couch, pillow, carpet, or stuffed animal that has recently been in contact with an infested person may result in transmission.  Of note, both nymph and adult lice forms need to feed on blood to live.  If an adult louse does not have a blood meal, it can die in 2 days.

Laboratory Diagnosis:
The diagnosis of pediculosis is best made by finding a live nymph or adult louse on the scalp or in the hair of a person.  Finding numerous nits within 6 mm of the scalp is highly suggestive of active infestation.  Finding nits only more than 6 mm from the scalp is only indicative of previous infestation.

Diagnostic findings

• Microscopy

Treatment:
Requires using either a prescription or an over-the-counter (OTC) medication.  For additional information, see the recommendations in The Medical Letter (Drugs for Parasitic Infections) or see CDC's Treating Head Lice Infestation at http://www.cdc.gov/ncidod/dpd/parasites/lice/factsht_head_lice_treating.htm.