Louse

Pediculus humanus capitis infests the scalp and is spread by direct head contact, common in schoolchildren and not a marker of poor hygiene; nits are cemented to hair shafts and treatment is permethrin or malathion. Pediculus humanus corporis lives in clothing seams rather than on the skin and is a disease of crowding, war, homelessness, and refugee settings; it alone transmits Rickettsia prowazekii (epidemic typhus), Bartonella quintana (trench fever, and also bacillary angiomatosis and culture-negative endocarditis), and Borrelia recurrentis (louse-borne relapsing fever, which recurs through antigenic variation of surface proteins). Control of body lice is achieved by laundering or discarding clothing and improving hygiene. Pthirus pubis, the crab louse, infests coarse hair and is sexually transmitted; its presence in a child should prompt evaluation for sexual abuse, and pubic lice on the eyelashes are treated with petrolatum. Finding lice warrants screening for other sexually transmitted infections in the case of P. pubis.