Louse

louse, (order Phthiraptera), any of a group of small wingless parasitic insects divisible into two main groups: the Amblycera and Ischnocera, or chewing or biting lice, which are parasites of birds and mammals, and the Anoplura, or sucking lice, parasites of mammals only. One of the sucking lice, the human louse, thrives in conditions of filth and overcrowding and is the carrier of typhus and louse-borne relapsing fever. Outbreaks of louse-borne diseases were frequent by-products of famine, war, and other disasters before the advent of insecticides (see infectious disease). Partly due to the widespread use of insecticidal shampoos for control, the head louse has developed resistance to many insecticides and is exhibiting a resurgence in many areas of the world. Heavy infestations of lice may cause intense skin irritation, and scratching for relief may lead to secondary infections. In domestic animals, rubbing and damage to hides and wool may also occur, and meat and egg production may be reduced. In badly infested birds, the feathers may be severely damaged. One of the dog lice is the intermediate host of the dog tapeworm, and a rat louse is a transmitter of murine typhus among rats.