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The susceptibility of local head lice to permethrin, sumithrin, deltamethrin, and carbaryl was determined by laboratory bioassays in field-collected colonies. Head lice collected from the infested heads of children 6-12 yr old were tested within 3 h of collection. The longest survival of control insects in the laboratory was obtained by keeping them in the dark at 18 degrees C and 70-80% RH. The base line susceptibility data obtained for insects collected from children not treated for lice, the reference colony, showed that deltamethrin caused the highest mortality of the insecticides tested (LC50, 0.06%). Permethrin, sumithrin, and carbaryl showed no significant difference in mortality (superposition of confidence intervals), being 10 times lower than that caused by deltamethrin. All field-collected lice required a higher LC50 of permethrin than the reference colony. Resistance levels varied from 3 to > 100 for colonies that were taken from children treated with anti-lice products. Lice colonies with permethrin resistance showed resistance to sumithrin and deltamethrin, but resistance was not observed to the carbamate carbaryl.
Histochemical stainings of head louse nits were performed and observations indicated that the nit sheath was nonchitinous. One discernable membrane composed of hyaluronic acid was established that encircled the larvae within the egg. The structural framework of the egg included a definite lattice around each aeropyle of the operculum, through which oxygen exchange occurred.
Head lice are very common and mainly affect children between 3 and 12 yr old. Little is known about the way nits, the eggs of the head louse, are attached to the hair. In this report, an objective measurement procedure for the ease with which nits can be removed is presented. The first peak force, associated with the start of nit movement, and the average and maximal force during the sliding of the nit were measured. The three force variables correlated with the length of the cylinder by which the nit was attached to the hair. A negative correlation was found between the maximum force exerted and the distance of the nit from the scalp. The method described in this report can be used to determine the in vitro efficacy of various products to remove nits.
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BACKGROUND: Millions of people are infested by head lice every year. However, louse transfer between hosts is not well-understood. Our goals were to determine: (1) which stages were most likely to disperse and why, (2) the likelihood of fomites transmission, and (3) if host blood gender affects louse development. METHODS: Various life stages of lice at differing densities were permitted to cross over a 15-cm hair bridge placed between two artificial blood-feeding arenas. Louse transfer caused by hot air movements, combing, toweling, and passive transfer to fabric was investigated. The ability of lice to oviposit on different foreign substrates and the hatching potential of eggs intermittently incubated for 8 h/night on a host were likewise investigated. Louse in vitro development following feeding on human female or male donor blood was compared. RESULTS: Adult lice were the most likely to disperse. Neither population density nor hunger significantly affected dispersal tendencies. Lice were dislodged by air movement, combs and towels, and passively transferred to fabric within 5 min. Females oviposited on a variety of substrates and 59% of eggs incubated for 8 h/night hatched after 14-16 days. There was no survivorship difference between lice artificially fed on female vs. male blood. CONCLUSIONS: Adult lice are the most mobile, indicating that they are most likely to initiate new infestations. Although head-to-head contact may be the primary route of transmission, less direct routes involving fomites may play a role and need further evaluation. Blood-borne factors do not appear to cause any gender-biased host preference.
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An estimated 6 to 12 million head lice infestations occur in the United States annually, with children ages 3 to 12 most likely to be affected. There are significant direct costs associated with treatment and indirect costs due to lost time from school. Anecdotal reports suggest that direct costs of treatment are in the hundreds of millions of dollars annually. Indirect costs are also substantial but more difficult to quantify. Examples of indirect costs include missed days from schools that use a "no nit" policy, lost wages for parents who must stay home with children, and costs of daycare for parents who cannot miss work. Contributors to the expense of treating head lice include misdiagnosis, and, consequently unneeded treatment; treatment failure due to misuse of pediculicides or other agents; and developing resistance, particularly to over-the-counter pyrethroid agents. An overview of direct and indirect costs of infestation are included in this review, along with a discussion of factors that lead to misuse and overuse of pediculicides. More accurate diagnosis of head lice infestation may provide the most effective means of controlling the costs of care and ensuring proper use of pediculicides.
BACKGROUND: The incidence of head lice infestations in North America is escalating with an estimated 12 million cases of head lice per year despite the existence of insecticidal therapies. OBJECTIVE: To evaluate certain characteristics of the human head louse, including their chitinous structure, nymphal developmental stages, legs with claw adaptations, antennae with sensory perceptions, and spiracles by which oxygen exchange occurs, for assessment of possible means to control the spread and growth of this insect. METHODS: Scanning electron-microscopic examination of head lice was performed. RESULTS: Newer treatments of head lice must acknowledge defense mechanisms that are based on anatomic structure and physiologic characteristics, details of louse transmission, and the insects' ability to 'resurrect' after sham death. CONCLUSIONS: An understanding of lice entomology is essential in the pursuit of novel means to control the lice epidemic.
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In the present study, pediculosis was investigated among a total of 2,725 children from 35 primary schools in Hsiulin District of Hualien County, Jenai District of Nantou County, Wulai District of Taipei County, Chienshih District of Hsinchu County, Fushing District of Taoyuan County, and Nanao District of Ilan County. The overall infestation rate was 12.8%. The rates by districts were 19.7%, 17.3%, 16.7%, 15.1%, 7.9%, and 3.0%, respectively. The pediculicides including Nix (permethrin 1%) 56 gm/tube, Para aerosol (bioallethrin 0.66%) 90 gm/tube, and Perioderm (malathion 1%) cream shampoo 40 gm/tube were used to treat the head louse infestation in 83, 91, and 103 children; the cure rates were 97.3%, 94.1%, and 93.4%, respectively. No significant differences were found in these rates. The reactions were slight and transitory. A total of 636 lice was collected from the hair using fine-toothed combs before treatment and from the used towels after treatment of children in Wulai, Chienshih, Hsiulin, and Jenai Districts. Each child was found infested with a mean of 7.7 lice. The mean intensity of infestation was highest in Jenai (9.3) and Chienshih (8.7) came next. Wulai (3.7) and Hsiulin (3.6) had lower intensities.
Head lice remain a common problem worldwide. As resistance to available therapeutic agents can emerge rapidly, there is a need for continued research to find new and better agents. Until better agents are available, clinicians may find that rotational therapy, using different agents, may help to slow the emergence of resistance. Physical modalities, such as mechanical nit and louse removal and occlusive agents to asphyxiate the lice, should not be ignored, especially in light of our limited therapeutic armamentarium. All therapeutic agents are doomed to failure if infestation is allowed to recur. Classmates, playmates, and family members of infested children should be inspected for head lice. Efforts should be directed at fomite control and nit removal. Louse infestation must be addressed as a community-wide problem. Body lice remain important vectors of disease. War, natural disaster, and poverty favor the spread of body lice. As we work to solve these seemingly eternal problems, we must develop better agents to treat infestation and prevent the spread of body lice.
Four pediculicides were tested against head lice in-vitro. The LT50 for Licid ranged between 10.75 (at conc. 50%) to 25.08 (at conc. 1%). All lice died with conc. 100% within 5 minutes. With Malathion, the LT50 ranged between 4.23 to 9.3 at conc. 50% to 1% respectively. All lice died with conc. 57% within 3 minutes. With Benzanil, the LT50 ranged between 20.85 to 44.34 at conc. 50% to 1% respectively. All lice died at conc. 2.5% within 10 minutes. With Para plus, the LT50 ranged between 18.46 to 29.5 at conc. 100% to 50% respectively. All lice died with conc. 100% within 30 minutes. So, the least time needed to kill all lice was given with Malathion (3 minutes). The least dose of pediculicide needed to kill all lice was those of Benzanil (1% = 0.025) and Malathion (1% = 0.57). The whole results were discussed regarding the advantages and disadvantages of these pediculicides.
The first finding of body lice in Czechoslovakia since year 1945 is demonstrated. The determination of the species is based on the location of the louse on the body of the infested person and on the significant differences in the length of tibia of middle legs in these lice and those collected from the head of children. Local eradication was achieved by using formulation containing permethrin, against head lice.