Permethrin-resistant human head lice,Pediculus capitis,and their treatment

OBJECTIVE: To compare the pediculicidal activity of Ovide lotion and its active ingredient, 0.5% malathion, with Nix and its active ingredient, 1% permethrin, in permethrin-resistant head lice. DESIGN: In vitro pediculicidal product and active ingredient comparison. The presence of knockdown resistance-type mutations (T929I and L932F) was validated by DNA sequencing. SETTING: University of Massachusetts-Amherst; University of Miami School of Medicine, Miami, Fla; Plantation and Homestead, Fla; and Mathis, Tex.Other PARTICIPANTS: Lice were collected in 3 geographical regions within the United States and in Yamburara, Ecuador, from healthy but infested individuals.Intervention Within 3 to 6 hours of collection, lice were given a blood meal, exposed to products or active ingredients, and observed at regular intervals. MAIN OUTCOME MEASURES: Percent mortality of lice at regular intervals after exposure to products or active ingredients and presence of T929I and L932F mutations. RESULTS: South Florida lice exhibited a significantly slower mortality response to permethrin compared with susceptible Ecuadorian lice. Ovide and malathion killed permethrin-resistant lice faster than Nix or permethrin. The presence of T929I and L932F in permethrin-resistant south Florida lice was confirmed by DNA sequencing. The population of Texas lice from Mathis was slightly resistant to permethrin and included 13% with resistant genotypes. CONCLUSIONS: The presence of the T929I and L932F mutations was confirmed by DNA sequencing in lice collected from children in south Florida that were resistant to the pediculicidal effects of permethrin and the leading permethrin-based head lice product, Nix. Malathion resistance was not observed in this study. The data also show that Ovide killed these same permethrin-resistant head lice approximately 10 times faster than permethrin or Nix.     

Scanning electron microscopy of adult head lice (Pediculus humanus capitis) with focus on clinical implications

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.     

Persistent head lice following multiple treatments: evidence for insecticide resistance in Pediculus humanus capitis

Viable head lice were found on the scalps of two family members following multiple topical insecticide treatments. The possibility of reinfestation had been reliably excluded. Persistent infestation could be diagnosed only after cutting the hair and combing repeatedly, which allowed visualization of juvenile (nymphal) and adult lice. Insecticide-resistant headlouse infestations are probably much more common than is generally realised and may persist unnoticed, so that more aggressive approaches will be needed to eradicate these ectoparasites from individuals and communities.     

Comparative efficacy of two nit combs in removing head lice (Pediculus humanus var. capitis) and their eggs

BACKGROUND: Fine tooth lice combs fall into two classes based on the material from which their teeth are made: plastic or metal. Metal combs are further divided into those that are made from a flat sheet of metal, and hence have rectangular teeth, and those that have cylindrical teeth embedded in a plastic base. METHODS: The efficacy of two fine tooth combs [Lice Meister comb (metal) and Lady Jayne comb (plastic)] in removing head lice (Pediculus humanus var. capitis) and their eggs from the hair of children was evaluated after treatment with a viscous head lice product (Lice Blaster; Emerald Forest Pharmaceuticals Pty Ltd, Currumbin, Qld, Australia). The hair of 27 children was divided into two sections sagitally, and each comb was randomly assigned to one half of the hair, and the lice and eggs removed by the combs were counted. RESULTS: In 96% of subjects, the Lice Meister comb removed more eggs than the Lady Jayne comb, with an average of three to four times more hatched, dead, and live eggs removed. The Lice Meister comb removed more lice than the Lady Jayne comb in 10 subjects, the same in eight subjects, and less in nine subjects. CONCLUSION: Overall, the Lice Meister comb is recommended as a more effective comb for use in controlling head lice infestations, whether employed with conditioner or with insecticide treatment. This appears to be the first study investigating the efficacy of nit combs in vivo. Further research is needed to determine which characteristics of fine tooth combs are the most important in removing head lice eggs.     

A comparison of botanical and synthetic substances commonly used to prevent head lice (Pediculus humanus var. capitis) infestation

BACKGROUND: Pediculosis, caused by head lice (Pediculidae: Pediculus humanus var. capitis), is experiencing a global resurgence, with the prevalence in primary schools averaging as high as 40% in some areas regardless of socioeconomic factors. Control efforts using chemical treatments are becoming increasingly ineffective, with insecticide resistance recorded in several countries. Prevention using repellents and oils would be useful if they limited transmission. Many commercially available substances reputedly have effective repellent qualities, but remain untested. METHODS: This study tested the preventative efficacy of N,N-diethyl-3-methylbenzamide (DEET) against several commercially available botanicals to clarify their value as transmission inhibitors, irritants, repellents, and antifeedants. RESULTS: The transfer of head lice to treated hairs was limited by the slippery nature of the oils rather than their repellent qualities. Irritancy was not important because lice proceeded despite being highly irritated, except in the case of coconut. Tea tree and peppermint caused the most repellence, and tea tree and lavender prevented some blood feeding on treated skin. Comparatively, tea tree oil was most efficacious, with DEET ranking equal second overall with coconut, peppermint, and a botanical mixture. CONCLUSIONS: Neither DEET nor any of the botanicals tested showed sufficient preventative efficacy to be endorsed.     

Effectiveness of isopropyl myristate/cyclomethicone D5 solution of removing cuticular hydrocarbons from human head lice (Pediculus humanus capitis)

ABSTRACT: BACKGROUND: In the treatment of human head lice infestation, healthcare providers are increasingly concerned about lice becoming resistant to existing pesticide treatments. Traditional pesticides, used to control these pests, have a neurological mechanism of action. This publication describes a topical solution with a non-traditional mechanism of action, based on physical disruption of the wax layer that covers the cuticle of the louse exoskeleton. This topical solution has been shown clinically to cure 82% of patients with only a 10-minute treatment time, repeated once after 7 days. All insects, including human head lice, have a wax-covered exoskeleton. This wax, composed of hydrocarbons, provides the insect with protection against water loss and is therefore critical to its survival. When the protective wax is disrupted, water loss becomes uncontrollable and irreversible, leading to dehydration and death. A specific pattern of hydrocarbons has been found in all of the head louse cuticular wax studied. Iso-octane effectively removes these hydrocarbons from human head lice's cuticular wax. METHODS: A method of head louse cuticle wax extraction and analysis by gas chromatography was developed. Human head lice (Pediculus humanus capitis) were collected from infested patients and subjected to any of three extraction solvents comprising either the test product or one of two solvents introduced as controls. A gas chromatograph equipped with a flame ionization detector (GC/FID) was used to determine the presence of hydrocarbons in the three head lice extracts. RESULTS: In the study reported herein, the test product isopropyl myristate/cyclomethicone D5 (IPM/D5) was shown to perform comparably with iso-octane, effectively extracting the target hydrocarbons from the cuticular wax that coats the human head louse exoskeleton. CONCLUSIONS: Disruption of the integrity of the insect cuticle by removal of specific hydrocarbons found in the cuticular wax appears to offer a mechanism for killing lice without the likelihood of encountering genetic resistance.     

Transmission potential of the human head louse, Pediculus capitis (Anoplura: Pediculidae)

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.     

Quantification of blood intake of the head louse: Pediculus humanus capitis

Although head lice, Pediculus humanus capitis, are globally prevalent blood-sucking ectoparasites, the amount of blood imbibed by head lice has not been determined. This study investigated this parameter, as regular loss of a small quantity of blood may lead to an iron deficiency and anaemia. Adult female lice (66), adult males (46), and nymphs (152) were weighed before and after feeding in groups of 17-109 lice. The average amounts of blood imbibed at a single feed were: adult female louse (0.0001579 ml), adult male (0.0000657 ml) and nymph (0.0000387 ml). Assuming three feeds per day by an average infection of 30 lice (10 females, 10 males, and 10 nymphs), the average child with active pediculosis would loose 0.008 ml of blood per day. This amount of blood loss is of no clinical significance even in iron-deficient children. The most heavily infected child observed with 2657 lice could be expected to loose 0.7 ml/day or 20.8 ml/month, which may be of clinical importance in a child on an adequate diet, and would be significant in an iron-deficient child. However, if head lice feed more often than three times a day, a heavy infestation would have a greater potential to lead to iron deficiency. The frequency of feeding of head lice on the head of the human host needs to be determined.     

Clinical and laboratory trials employing carbaryl against the human head-louse, Pediculus humanus capitis (de Geer)

Carbaryl was very effective against head lice when used as a 0·5%, lotion or a 0·5%, shampoo at a dose of 50 mg active ingredient per head. Unexpectedly good ovicidal and residual effects were found, especially when carbaryl was employed as a lotion. These effects equalled those of malathion and exceeded those of gamma-benzene hexachloride (HCH or Lindane), bioresmethrin and chlorphenamidine. The ovicidal effect was also demonstrated in the laboratory, but shown to be highly thermo-labile. It was also shown that the only known form of malathion resistance in any of the human lice does not extend to carbaryl.     

Comma hairs in tinea capitis: a useful dermatoscopic sign for diagnosis of tinea capitis

Diagnosis of tinea capitis (TC) can be challenging for dermatologists, especially in noninflammatory TC caused by anthropophilic dermatophytes and in black patients, in whom erythema of the scalp is difficult to appreciate. The finding of a typical TC dermoscopic pattern may lead more quickly to a correct diagnosis.     

Permethrin 1% Creme Rinse for the Treatment of Pediculus humanus var capitis Infestation

Permethrin 1% creme rinse (NIX) was tested as a treatment for Pediculus humanus var capitis (head lice) in a placebo-controlled, double-blinded, randomized study. As a positive control, a third arm of the study included nonrandomized, but investigator-blinded, treatment with 1% lindane shampoo (Kwell). At 14 days after treatment, 97% of patients treated with permethrin were free of lice compared to 6% of placebo-treated patients (P less than 0.001) and 43% of the lindane-treated group. Permethrin was 70% ovicidal compared to 14% for placebo (P less than 0.001) and 45% for lindane. No adverse experiences were noted during this study. Permethrin 1% demonstrated high pediculicidal and ovicidal activities, which in combination with its low mammalian toxicity, residual activity, and cosmetic properties, make it an excellent treatment for pediculosis capitis.     

头癣诊疗指南（2008版）

经过中华医学会皮肤性病学分会真菌学组及国内相关知名专家反复讨论和修改,制定了真菌性皮肤病诊疗指南系列,将陆续刊出供国内同行参考.参加本指南制定的专家为(按姓氏汉语拼音排列):金学洙、李若瑜、李春阳、刘维达、赖维、冉玉平、温海、席丽艳、郑岳臣.     

Evidence for double resistance to permethrin and malathion in head lice

A rising prevalence of head lice among school children and rising sales of insecticides with anecdotal evidence of their treatment failure, led us to examine whether head lice in Bristol and Bath were resistant to the insecticides available for treating head lice. Ten schools in Bristol and Bath were visited to collect field samples of head lice. A comparison was made of the survival rates of fully sensitive laboratory reared body lice and field samples of head lice on insecticide exposure. To confirm the in vitro relevance of these tests we performed supervised treatments of affected subjects with malathion or permethrin. There were significant differences (P < 10-6 Fishers exact test) between head and body lice survival for malathion and permethrin exposure, but not for carbaryl. There was an 87% failure rate for permethrin and a 64% failure rate for malathion with the topical treatment of a selected number of infested school children. We conclude that there is a high resistance to permethrin and malathion, but head lice remain fully sensitive to carbaryl. This is the first report of doubly resistant head lice. As permethrin, phenothrin (a very similar synthetic pyrethroid) or malathion are the active ingredients in all the over-the-counter head lice treatments in the U.K., then it is likely that head lice prevalence will continue to increase. The resistance against permethrin employed by the head louse is probably the kdr (knockdown resistance) mechanism, and an enzyme-mediated malathion-specific esterase is the likely mechanism against malathion.     

Assessment of topical versus oral ivermectin as a treatment for head lice

Many medications are available for treatment of pediculosis capitis including ivermectin. Our aim is to compare the efficacy and safety of topical versus oral ivermectin in treatment of pediculosis capitis. Sixty‐two patients with proved head lice infestation were included and divided into group I (31 patients; received single topical application of 1% ivermectin) and group II (31 patients; received single dose of oral ivermectin). Treatment was repeated after 1 week for nonresponders. At 1 week after treatment, the eradication rates and improvement of pruritus were significantly higher among patients who received topical than oral ivermectin. When a second treatment, topical or oral, was given to nonresponders, the cure rates of infestation and pruritus was 100% and 97% among patients treated with topical and oral ivermectin, respectively with no significant difference between the two groups. This study suggests that both topical and oral ivermectin demonstrate high efficacy and tolerability in treatment of pediculosis capitis. However, a single treatment with topical ivermectin provides significantly higher cure of infestation and faster relief of pruritus than oral ivermectin. In addition, whether topical or oral ivermectin is used to treat head lice, a second dose is required in some cases to ensure complete eradication.