Abstract
Sucking lice (Phthiraptera: Anoplura) are obligate blood-feeding ectoparasites of placental mammals including humans. Worldwide, more than 550 species have been described and many are specific to a particular host species of mammal [1]. Three taxa uniquely parasitize humans: the head louse, body louse, and crab (pubic) louse. The body louse, in particular, has epidemiological importance because it is a vector of the causative agents of three important human diseases: epidemic typhus, trench fever, and louse-borne relapsing fever. Since the advent of antibiotics and more effective body louse control measures in the 1940s, these diseases have markedly diminished in incidence. However, due to 1) increasing pediculicide resistance in human lice, 2) reemergence of body louse populations in some geographic areas and demographic groups, 3) persistent head louse infestations, and 4) recent detection of body louse-borne pathogens in head lice, lice and louse-borne diseases are an emerging problem worldwide. This mini-review is focused on human body and head lice including their biological relationship to each other and its epidemiological relevance, the status and treatment of human louse-borne diseases, and current approaches to prevention and control of human louse infestations.
Highlights
Scientists have argued about the exact taxonomic and biological relationships between human head lice and body lice and, in particular, whether they represent a single species with two ecotypes or two distinct species [2,3]
Differences between head and body lice in the complex developmental interactions that maintain Riesia between generations have been described [8], but whether these differences occur in all louse populations is unknown
100% ovicidal [38]. 3Partial ovicidal activity of permethrin has been reported [41]. 4At baseline, 38% of body lice collected from homeless were resistant to permethrin [43]. 5Possibility of occurrence of ivermectin resistance in body lice has been demonstrated in laboratory settings [44]. doi:10.1371/journal.ppat.1003724.t002
Summary
Lighter 2.4–3.6 mm 2.3–3.0 mm Longer and narrower Slightly longer than wide Not prominent Not extending into intersegmental membranes 8–12/day Clothing fibers esp. along seams Up to 60 days 1–5/day A are located on 18 minicircles, each containing one to three genes, and the intergenic regions are variable in each louse likely as a result of numerous recombination events that make those regions unsuitable for genetic analysis [6]. The extensive movement of lice over the human body in populations with both head and body pediculosis makes collections from each louse ecotype rather difficult. The hope that the global movements of people and their lice have not completely obscured the evolution of lice and the origins of human populations was further enhanced by development of a qPCR assay that distinguished head and body lice from 13 countries based on the PHUM540560 gene, which was expressed differently in transcriptome studies of head and body lice [20,21]. Head lice cause medical and psychological problems in their own right, the hypothesis that body lice have emerged repeatedly from head louse populations compounds their potential epidemiological importance [2,14]. Dorsal view of ethanol-preserved female head louse; D. Dorsal view of ethanol-preserved male head louse. All photographs were taken using a Visionary Digital K2/SC long-distance microscope (Infinity Photo-Optical Company, Boulder, CO), courtesy of Lorenza Beati. doi:10.1371/journal.ppat.1003724.g001
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