Head lice: scientific assessment of the nit sheath with clinical ramifications and therapeutic options.

Head lice, like many insects, produce a protective coating for their newly laid eggs that is essential to the survival of the species. Knowledge of the composition of the sheath, which is the glue by which the egg is attached to human hair, and the nit laying process could lead to production of agents that could be used to attack louse infestations by interfering with the normally protected environment of nymph development within the egg. The physical removal of nits has become an important part of treatment of head louse infestations given the "no-nit" policy in schools. Biochemical analysis has revealed that the nit sheath of the head louse is composed of 4 bands of protein, possibly cross-linked to aliphatic components with a tertiary structure of beta sheeting. Nature has protected the louse by making the nit sheath similar in composition to the hair; thereby, agents designed to unravel the nit sheath may also damage human hair. Possible targets to destroy the nit sheath include proteases, denaturants, beta sheet breaker proteins, and small protein inhibitors of sheath formation. Better understanding of insect glues may allow us to develop compounds so that the liquid secretions of the collateral glands of the female louse, which becomes the nit sheath, do not solidify by oxidation when placed with the louse egg onto human hair. Knowledge of insect behavior, such as oviposition, may also suggest methods for repelling female lice from laying eggs onto hair. Alternatively, agents that coat the nits and restrict the oxygen transfer to the developing larvae may prove beneficial.