LOUSE

plural lice a member of one of some 3,300 species of small, wingless, parasitic insects of the order Phthiraptera. There are two main suborders of lice, the Mallophaga and the Anoplura. The former, also known as biting, or chewing, lice, are parasitic on birds and various types of mammals. They feed on the softer parts of feathers, scales, skin, and hair and occasionally on dried blood. The Anoplura, also known as sucking lice, are parasitic only on mammals, including humans. These lice live exclusively on the blood of their hosts. A third suborder, Rhynchophthirina, consists of two species that parasitize elephants and African warthogs. The body of a louse is flattened and is divided into head, thorax, and abdomen. The eyes, antennae, and mouthparts are all located on the head. The eyes are occasionally absent; when present they are sensitive only to light and dark. The antennae are short. The structure of the mouth depends on the type of louse. Mallophaga have mouthparts suitable for biting and chewing. Anoplura have three retractable stylets that can be thrust into the skin; blood is sucked into the mouth while a special substance is added to prevent coagulation. The thorax is small and bears three pairs of short legs that end in claws or hooks, enabling the louse to grip its host securely. The abdomen is flat and nearly transparent. Lice spend their entire lives on the body of the host animal, with the sole exception of the human body louse, which lives in clothing. The eggs are cemented to the hair or plumage of the host and are known as nits. Many eggs are laid, and under the right conditions lice multiply rapidly; it has been estimated that a single female can produce 5,000 offspring in about eight weeks. The nits hatch in about one to two weeks. The nymphs undergo a gradual and partial metamorphosis in the course of three molts, reaching adult form in about a month. Species of lice are parasitic on specific host species, and little evidence of transfer from one host species to another is known. Among host species, infestation is virtually universal in the wild. In domesticated animals, heavy infestations cause much irritation; animals may scratch and rub against objects to relieve the irritation, injuring their fur or hide in the process and sometimes causing secondary infections. In moving from one host animal to another, lice may spread many diseases, including tapeworm in dogs and murine typhus in rats. The lice that infest human beings are mainly Pediculus humanus, with varietal or subspecific names according to sites of infestation; colloquially they are referred to as head lice (P.h. capitis) or body lice (P.h. corporis). The pubic, or crab, louse (Phthirus pubis) also affects humans. Louse infestations tend to be widespread under conditions of overcrowding and inadequate hygiene. Head lice spread by direct personal contact and through the sharing of hats, combs, etc. Body lice also spread by person-to-person contact and through shared clothing and bedding. The transmission of pubic lice is primarily venereal. Louse infestations provoke substantial irritation and may lead to secondary infections, particularly impetigo in children. In addition, the body louse is a major carrier of the organisms that cause relapsing fever, trench fever, and typhus. Louse infestations can be quickly cured with shampoos, soaps, and lotions that contain benzene hexachloride; the disinfection of clothing, bedding, and other shared articles is necessary to prevent the spread of the parasites. plural lice, any member of the order Phthiraptera, small, wingless, parasitic insects divisible into two main groups: the Mallophaga, 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, is the carrier of typhus and louse-borne relapsing fever; it thrives in conditions of filth and overcrowding. Outbreaks of louse-borne diseases were frequent by-products of famine, war, and other disasters before the advent of powerful insecticides (see infection). 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 affected; 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. Additional reading G.F. Ferris, The Sucking Lice, Mem. Pacif. Cst. Ent. Soc., vol. 1 (1951), an outline of the morphology, growth, and identification of the Anoplura, with a host-parasite list; G.H.E. Hopkins, The Host-Associations of the Lice of Mammals, Proc. Zool. Soc. Lond., 119:387604 (1949), an account of the biology and methods of preservation, examination, and distribution of the mammalian lice, with a list of mammals and their lice; and with T. Clay and G. Timmermann, First Symposium on Host Specificity Among Parasites of Vertebrates (1957), papers on the distribution of the Anoplura and Mallophaga of birds and mammals, with a discussion on host-parasite relationships; S. von Kler, Bibliographie der Mallophagen, Mitt. Zool. Mus. 36:147403 (1960), a full bibliography of the literature on the Mallophaga arranged chronologically, together with an author and subject index; M. Rothschild and T. Clay, Fleas, Flukes and Cuckoos: A Study of Bird Parasites, 3rd ed. (1957), a popular account of the Mallophaga of birds; H. Zinsser, Rats, Lice and History (1935, reprinted 1985), a readable account of the scientific and historical aspects of Typhus. Theresa Clay