Head lice

The two species that belong to this group include Pediculus humanus capitis (head louse) and P. humanus corporis (body louse). The eggs (or nits) remain firmly attached to the hair, and in about 10 days the lice hatch to form nymphs, which mature in 2 weeks. The lice become attached to the base of the hair follicle and feed on the blood of the host.10 Pubic or crab lice are found on the hairs around the genitals, but may occur... 

Phthiriasis palpebrarum is an imcommon eyelid infestation by Phthiruspubis (crab louse) and, less commonly, by the Pediculus bumanus species, P. humanus var. capitis (head louse) and P humanus var. corporis (body louse). The term pediculosis refers to infestation by the two P humanus species and should not generally be used when referring to eyelid manifestations. 

Three species of lice occur as parasites on humans. These lice are blood suckers, and they can be disconcertingly abundant under unsanitary conditions. The human louse, Pediculus humanus, occurs as two races, which feed on different parts of the body. The head louse, capitis race, occurs in the hairs of the head, to which it attaches its whitish eggs, also known as nits. The body louse corporis race, also known as the cootie, feeds on the human body, and hides and lays its... 

It is a potent cholinesterase inhibitor that prevents the breakdown of acetylcholine and interferes with neuromuscular transmission in the head louse, paralysing it and preventing it from feeding. It is oil-soluble and absorbed by a process of passive diffusion through the lipid coat of both insect and egg achieving a lethal dose depends on the concentration of the product and the length of contact. 

Head louse infestations periodically cause disruptions at schools aii over the world. The treatment with pyrethrins and PBO is relatively cheap, and effective. The most common formulations contain either 0.15% or 0,3% pyrethrins synergized with 3.0% PBO formulated into non foaming shampoos (water- based pm-sized emulsions) that are applied directly to the affected area and repeated after i week to kill any newly hatched lice. The pediculicidal and ovicidal efficacy of synergized pyrethrins arc enhanced in shampoo formulations as a result of the surface-tension-lowering action of the formulation and are preferable to direct applications of lotions. 

Figure 1 4. Light micrograph illustrating empty nits of the head louse Pediculus capitis on a human scalp hair. Kindly provided by John T. Wilson.

It is not certain when people first started wearing elothes. Scientists estimate that this happened more than 100,000 years ago, beeause the body louse (pediculus humanus humanus) apparently diverged from the head louse (pedi-culus humanus capitis) at that time. The first elothes were made from natural materials animal skin and furs, grasses and leaves and the first needles are recorded about 30,000 years ago. 

Burgess, 1. R, Brunton, E. R., Burgess, N. A. 2010. Clinical trial showing superiority of a coconut and anise spray over permethrin 0.43% lotion for head louse infestation, 1SRCTN96469780. Ear. J. Pediatr. 169(l) 55-62. 

The activity of essential oils against the human head louse, Pediculus humanus capitis, has been investigated in a nnmber of reports. Nnmerons essential oils have been found to exhibit... 

Sodium Channel Point Mutations Associated with Pyrethroid Resistance in the Head Louse, Pediculus humanus capitis... 

Reduced Na" channel sensitivity in pyrethroid-resistant head lice was first suggested by Hemmingway et al. (25). In pyrethroid-resistant head louse colonies from the US and the UK, resistance-specific two concomitant amino acid substitutions were commonly identified as kdr-VkQ mutations at DII S5 of para Na channel (26). Their analysis was based on a partial cDNA sequence of as many as 132 amino acid residues including Dll S3 and S6. Analysis of the whole coding sequence is a prerequisite for the development of molecular diagnosis or the study of the genetic origins of kdr-Vke mutations in head lice. 

Figure 4. Phenothrin susceptibilities of head louse colonies.

Pyrethroid-resistance of head lice was discriminated with phenothrin at 100 mg/m by the method of continuous contact of insecticide-impregnated filter paper for 3 hours. We first identified pyrethroid-resistant head lice colonies in Japan. Pyrethroid pediculicides seemed to be out of use for the resistant colonies, however, the resistance has not been an overwhelming majority in Tokyo metropolitan area. The complete coding sequence of poru-orthologous Na channel was determined in the head louse and resistance-associated four amino acid substitutions were commonly identified in the Na channel from the three resistant colonies tested. 

Kazan L, Berg JE, Bowman JP, Murray JV, Ryan WG. Pharmacokinetics and safety of 0.5% ivermectin lotion for head Louse infestations. Pediatr Dermatol 2013 30(3) 323-8. 

Pediculosis caused by Pediculus capitis, the human head louse, is the most prevalent parasitic infestation of humans worldwide, especially among school children of 3-12 years old (7). More Uian 6-12 million people in the United States (US) are estimated to have pediculosis. Synq>toms of infestations are relatively mild, but the social, mental and economic consequences are substantial. Pediculosis is not widely tolerated in the US and is repeatedly treated by a variety of over-the-counter pediculicides, which are exclusively limited to those containing pyrethrin or permetfarin as active ingredients. Because these pediculicides share a common mechanism of action on the voltage-sensitive sodium channel in the nervous system of insects (2), dieir repetitive and continued use has imposed a high pressure for the selection of resistant louse populations. 

In this article, the level of susceptibility to various insecticides in different human head louse populations in the US was investigated to assess the distribution of resistance. We also reported on the molecular mechanisms of head louse resistance to pyrethroid mediated by sodium channel mutations. Also discussed were the genotyping techniques for resistance monitoring and the... 

Insecticide-susceptible strains of body louse from Israel (IS-BL) and head lice from Panama (PA-HL) and Ecuador (EC-HL) have been previously described 10,14). Another permethrin-susceptible strain of head louse was collected from Seoul, Korea (KR-HL). Permethrin-resistant strains of head louse were obtained from Western Massachusetts (MA-HL), Plantation, Florida (FL-HL), Homestead, FL (SF-HL), San Bernardino County, California (SC-HL) and four locations in Texas (TCC-HL, TMF-HL, TMS-HL and TSA-HL). A petmeduin- and malathion-resistant strain (BR-HL) of head louse was provided by G. Coles (University of Bristol). 

Molecular Mechanisms of Head Louse Resistance to Pyrethroids and Development of Monitoring Tools for Resistance Management... 

OHsubunit genes from several populations of head louse. The M815I,... 

Figure 4, Relationship between phenotypic resistant level (LTsq and percentage of resistant homozygotes (T9171 and L920F) in different head louse populations from Ecuador, Florida and T cas...

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