Transmission potential of the human head louse, Pediculus capitis (Anoplura: Pediculidae)

Millions of people are infested by head lice every year. However, louse transfer between hosts is not well-understood. Our goals were to determine: (1) which stages were most likely to disperse and why, (2) the likelihood of fomites transmission, and (3) if host blood gender affects louse development.

Various life stages of lice at differing densities were permitted to cross over a 15-cm hair bridge placed between two artificial blood-feeding arenas. Louse transfer caused by hot air movements, combing, toweling, and passive transfer to fabric was investigated. The ability of lice to oviposit on different foreign substrates and the hatching potential of eggs intermittently incubated for 8 h/night on a host were likewise investigated. Louse in vitro development following feeding on human female or male donor blood was compared.

Adult lice were the most likely to disperse. Neither population density nor hunger significantly affected dispersal tendencies. Lice were dislodged by air movement, combs and towels, and passively transferred to fabric within 5 min. Females oviposited on a variety of substrates and 59% of eggs incubated for 8 h/night hatched after 14-16 days. There was no survivorship difference between lice artificially fed on female vs. male blood.

Adult lice are the most mobile, indicating that they are most likely to initiate new infestations. Although head-to-head contact may be the primary route of transmission, less direct routes involving fomites may play a role and need further evaluation. Blood-borne factors do not appear to cause any gender-biased host preference.