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The aim of this work was to determine head lice parasitism intensity by Pediculus humanus capitis and its variation, according to both gender and age in 181 school children of a primary school. The intensity was higher among 6 to 8-year-old girls. Pediculosis intensity diminishes significantly between 9 and 11 years of age in both sexes.
New alternative insecticides are necessary for the chemical control of head lice. In this study the fumigant knockdown time 50% (KT50) and repellency index (RI) of three aliphatic lactones was compared with two essential oils and DDVP, against permethrin-resistance Pediculus humanus capitis from Argentina. In the fumigant assay, none of the lactones were effective compared to the highest activity of eucalyptus (KT50 15.53 m). In the repellency test, the three lactones were equally or more effective (RI ranging from 60.50 to 76.68) than the positive control (piperonal). These lactones are promising as head lice repellents.
The repeated use of permethrin and other insecticides for the control of head lice, Pediculus humanus capitis De Geer (Anoplura: Pediculidae), during past decades has resulted in the development of marked levels of resistance. Thus, new alternative insecticides are needed for the control of head lice. We studied the fumigant and repellent properties of essential oils from 16 native and exotic plants in Argentina, and 21 chemical components against permethrin-resistant head lice from Argentina. With a direct vapor-exposure bioassay, the most effective oil was from the native Myrcianthes cisplatensis Cambess (Myrtaceae) with a time to 50% knockdown (KT50) of 1.3 min, followed by exotic species, Eucalyptus cinerea F.V. Muell., Eucalyptus viminalis Labill., and Eucalyptus saligna Smith. with KT50 values of 12.0, 14.9, and 17.4 min, respectively. The most effective components were 1,8-cineole and anisole, with KT50 values of 11.1 and 12.7 min, respectively. Regression analysis of KT50 values and vapor pressures and water-partition coefficients for the essential oil components revealed that the most effective fumigants were among the more volatile components. Repellency assays indicated that the essential oil from Mentha pulegium L. and its benzyl alcohol component were the most effective repellents, having repellency indices of 75.5 and 57.8%, respectively. Thus, some Argentinean plants contain essential oils and components that function as fumigants or as repellents and thereby show potential for development of new control products for head lice.
Head lice are caused by the host-specific, ectoparasitic insect Pediculus humanus capitis De Geer and remain a common human infestation. As a response to increasing resistance of head lice to present insecticidal agents, additional agents must be pursued. Inasmuch as nicotine has been used for controlling poultry lice, an in vitro study assessing its possible usage for human head lice was performed. Nicotine proved not to be an efficient insecticide, although it may facilitate removal of adult lice because it induces muscle twitches that may affect the insect's normal grip on hair follicles.
Permethrin-resistant colonies of Pediculus capitis (De Geer) from Buenos Aires were used to establish a resistance profile and to examine resistance mechanisms. All permethrin-resistant head lice (resistance ratio from 52.8 to > 88.7) were also resistant to d-phenothrin (resistance ratio from 40.86 to > 48.39) and deltamethrin (resistance ratio from 16.24 to 38.06). No cross-resistance to carbaryl was found in any of the pyrethroid-resistant P. capitis tested. Otherwise, all resistant colonies showed low to high levels of resistance to beta-cypermethrin. This pyrethroid had never been applied as a pediculicide in Argentina; however, the high level of resistance found in these permethrin-resistant colonies (resistance ratio from 9.74 to 50.97) demonstrated that pyrethroid cross-resistance occurred to this novel insecticide. Treatment with piperonyl butoxide (PBO) or triphenylphosphate (TPP) significantly decreased the toxicity of permethrin in the four colonies tested. The esterase inhibitor TPP produced lower enhancement of toxicity than the multifunction oxidase inhibitor PBO in the colonies having the highest resistance levels. Results presented here concerning the cross-resistance profile and synergism by enzyme inhibitors in permethrin-resistant head lice demonstrated that enhanced metabolism was involved in the pyrethroid resistance. However, the substantial degree of resistance that remained after synergism suggested the presence of another resistance mechanism. Cross-resistance to pyrethroid and susceptibility to the carbamate carbaryl suggested a common action mechanism.
The effectiveness of 1-octanol, 1-nonanol, 1-decanol, 1-undecanol, and 1-dodecanol was evaluated by immersion method against susceptible and permethrin-resistant head lice, Pediculus humanus capitis De Geer, from Buenos Aires, Argentina. All the tested alcohols showed knockdown effect at 10 min and mortality 18 h after treatment. The highest activity was found for the 1-dodecanol (KC50 2.55%, LC50 2.28%) and the lowest for 1-octanol (KC50 8%, LC50 4.46%). The toxicity to the head lice systematically increased with the increase in carbon atoms in the n-aliphatic alcohol moiety, and with the octanol:water coefficient (r2 = 0.94). The pediculicidal activity of 1-dodecanol was not correlated with resistance to permethrin, because no significant difference was observed between toxicity parameters in the susceptible (MAR) and the permethrin-resistant populations which had different resistant levels (RR 5.77 x for E49 population, RR 9.5 x for HL population and RR > 35.3 x for GH population). The pediculicidal effect of aliphatic alcohols demonstrated in this study and the lack of correlation with the permethrin resistance may prove to have a practical value for use in susceptible and permethrin-resistant head lice control.
Permethrin has been used extensively for control of Pediculus humanus capitis De Geer (Anoplura: Pediculidae) in Argentina since 1990, resulting in the development of resistance to this and other pyrethroids. This resistance was first detected in some field populations in 1997. A survey for resistance in Buenos Aires in 2001 revealed significant resistance levels in lice on children at 24 of 26 (92.3%) schools. When compared with a previously unexposed reference population, resistance ratios (RRs) obtained by exposing the insects to filter papers impregnated with permethrin ranged from 2 to 60 in 10 (39%) of the schools. RRs in the remaining 14 (61%) populations were too great to not be measured with the filter paper method (RR > 88.7). As an alternative, we used topical applications of 0.1 microl of acetone solution of permethrin on the dorsal abdomen of adults and third instars. This topical method, which has not been previously reported for head lice, was capable of quantifying higher levels of resistance. Highly resistant populations had RRs from 162.5 to 655.2. When applied to populations with low and intermediate levels of resistance, results from the filter paper and topical application methods were highly correlated, and RRs from topical application were higher than those from the filter paper method. Results from the combination of the two methods indicated that head lice among Buenos Aries school children are highly resistant to permethrin, and the resistance is widespread.
Four geographically distinct colonies of the human head louse, Pediculus humanus capitis De Geer (Anoplura: Pediculidae) were reared on a live host and exhibited significantly different life history patterns. Florida head lice exhibited approximately 10% slower development and approximately 15% reduced longevity relative to California or Ecuador head lice. Fecundity (4.9 +/- 0.2 eggs/female/d) and fertility (76.4 +/- 2.9% mean hatching rate) declined over the lifetime of female lice, especially when separated from males (i.e., unmated recently). All four colonies (above plus one from Panama) were similar in their ability to tolerate starvation, although older stages tended to die sooner. An in vitro feeding apparatus was developed to rear head lice. Teneral first instar lice were placed on human hair tufts on the upper side of membrane-covered feeders, which were immersed bottom-side down within a vessel containing warmed human blood. Relative to lice reared on a human host, in vitro-reared lice required a significantly longer time (10-20%) to molt and survived a significantly shorter time as adults (30-50%); the addition of antibiotics did not adversely affect louse development. Teneral first instars were more likely than any other stage to feed through the membrane. Lice spent a significantly greater proportion of time searching in the in vitro apparatus than on a host, but the proportion of time spent feeding did not differ. This research is the first to demonstrate that head lice can be reared successfully in vitro through a complete life cycle.
The insecticidal activity of 54 plant essential oils against female Pediculus humanus capitis De Geer was examined using direct contact and fumigation methods, and compared with the lethal activity of delta-phenothrin and pyrethrum, two commonly used pediculicides. In a filter paper contact bioassay with female P. humanus capitis, the pediculicidal activity was more pronounced in eucalyptus, marjoram, pennyroyal, and rosemary oils than in delta-phenothrin and pyrethrum on the basis of LT50 values at 0.0625 mg/cm2. At 0.125 mg/cm2, pediculicidal activity of cade, cardamone ceylon, clove bud, myrtle, rosewood, and sage oils was comparable with that of the test insecticides. In fumigation tests with female P. humanus capitis at 0.25 mg/cm2, eucalyptus, marjoram, pennyroyal, and rosemary oils were more effective in closed containers than in open ones, indicating that the effect of these oils was largely a result of action in the vapor phase. Neither delta-phenothrin nor pyrethrum exhibited fumigant toxicity. The essential oils described herein merit further study as potential control agents for P. humanus capitis.
Protein and lipid compositions were studied at different developmental stages of Pediculus capitis De Geer 1778. Phosphatidylcholine was found to be the predominant lipid at all stages and in both sexes. Palmitic and oleic acids were the main fatty acids throughout the 3 stages studied. A marked decline was observed in the total lipid content and triacylglyceride concentration during development, suggesting that their consumption is an energy source. The electrophoretic mobility revealed the predominance of a 320-kDa protein in eggs and adult females, whereas 2 major proteins of 514 and 439 kDa were found in nymphs, as well as in male and female adults. Two very high density lipoprotein fractions were isolated by ultracentrifugation of egg cytosol in a density gradient of NaBr. Both reserve lipoproteins contained phospholipids and triacylglycerols as the predominant lipids and a protein band of around 320 kDa. The structure of this band is likely to be similar to that found in females in a vitellogenic state.
Pediculosis humanus capitis (head lice) is an important public health problem among school children. In our study, 20,612 schoolchildren (10,367 boys, 10,245 girls) were examined for Pediculus humanus capitis in 36 elementary schools between December 1996 and February 1998 in Ankara, Turkey. The prevalence of pediculosis capitis infestation was found to be 3.4% (701/20,612). Of these, 382 students were treated with application of 1% permethrin cream rinse, and 184 students with 0.4% d-phenothrin shampoo. On day 14 of the controlled trial, the success rates were 93.7% in the 1% permethrin cream rinse group and 75.5% in the 0.4% d-phenothrin shampoo group. The 1% permethrin cream rinse was also significantly more active in pediculicidal efficacy when compared to the 0.4% d-phenothrin shampoo (p<0.001). As a result, these findings demonstrate that pediculosis capitis still remains a widespread health problem.
We studied the profile of permethrin resistance in populations of head lice infesting children 6-12 yr old in schools and their homes in and around Buenos Aires, Argentina. Five permethrin-resistant populations with different levels of resistance were collected: Hogar Loyola (HL), Republica de Turquia (RT), Hogar Mitre (HM), Guardia de Honor (GH), and Ricardo Guiraldes (RG). One susceptible population, Bandera Argentina (BA), also was collected. Their level of resistance was evaluated, and results showed resistance ratios of 13 for HL, 16 for RT, 22 for HM, 61 for GH, and 69 for RG. To elucidate the possible involvement of the cytochrome P450 monooxygenase system in conferring permethrin resistance, ethoxycoumarin-O-deethylase (ECOD) activity was measured in abdomens of individual third instars and adults by using a fluorometric assay. The ECOD activity was lower in the susceptible BA population (4.7 ng per louse) than in the resistant ones (13.7 ng per louse for RG, 12.3 ng per louse for GH, 8.6 ng per louse for RT, and 8.2 ng per louse for HL). ECOD activity was significantly correlated with the level of resistance in the field populations (r = 0.97, P = 0.0009), suggesting a role for cytochrome monooxygenase P450 system in permethrin resistance by head louse, Pediculus humanus capitis De Geer.
The ultrastructure of the Malpighian tubes in human louse Pediculus humanus corporis has been studied. The cells of the Malpighian tubules have the uniform structure: the apical surface is covered with microvilli, the basal plasmatic membrana forms relatively small invaginations. The microvilli are most developed in cells of the proximal department of the Malpighian tubules. Microvilli of the apical surface of the cells do not contain mitochondria which are localized mainly in supranuclear part of the cell. Cells are lined with a homogenous basal membrane.
By using the naked eye examination and comb method, a field survey and combing collection of head louse (Pediculus humanus capitis) among school girls in three different area (Man-Chow, Nan-Ao and Chuang-Wei) of Taiwan were performed from July 1979 to February, 1980. The general infestation rate of head louse was 39.8% (or 998/2,509). In the primary schools, comparatively, the rate at Man-Chow (66.7%) was highest, the next at Nan-Ao (55.4%) and the lowest at Chuang-Wei (39.4%). While in the junior high schools, the rate was apparently higher at Nan-Ao (38.4%) than that at Man-Chow (15.6%) and Chang-Wei (12.0%). The highest rate in the primary schools was found in 3rd graders except at Chuang-Wei in 5th graders. The corresponding figure in the junior high schools was found in 1st graders except at Nan-Ao in 2nd graders. Of 774 infested girls studied, according to the number of lice per infested girl, the percentages of infestation in the 5 groups were: the very light (nits only) 54.5, light (1-10) 38.5, moderate (11-50) 6.5, heavy (51-100) 0.4 and very heavy (over 100) 0.1 respectively. Of 2,178 head lice examined, 53.0% was nymphs; 28.7% females; 18.2% males. The average number of head louse in each infested girl 6.2.
It has been shown that during feeding the midgut epithelium of the human louse Pediculus humanus corporis consists of three types of cells: secretory, digestive, and reserve (regenerative) ones. According to the ultrastructural organization the secretory cells are subdivided into two regions--apical and basal. In the apical region of the secretory cells no microvilli are observed. The basal region contains mitochondria, ribosomes, rough endoplasmatic reticulum, microvesicular bodies and secretory granules. Three types of secretion of digestive enzymes (macroapocrine, microapocrine and merocrine ones) were found. The apical surface of the digestive cells is covered with microvilli; the cytoplasm of the digestive cells is filled with lipids and glycogen granules. Cells are lined with a homogeneous basal membrane.
The incidence of Pediculus humanus capitis infestation in pre-school and schoolchildren in Mahé, Seychelles, was investigated. High infestation rates were discovered, particularly in urban schoolchildren at district schools. Infestation in pre-schoolchildren increased with age. Girls were more infested than boys. Control of infestation will not be possible using only the child health service and the school health service. A combined approach is necessary based on the family unit.
Essential oils of aniseed, cinnamon leaf, red thyme, tea tree, peppermint, nutmeg, rosemary, and pine were tested in vitro against lice, Pediculus humanus. All the oils except for rosemary and pine were found to be effective in the laboratory when applied in an alcoholic solution and followed by a rinse the following morning in an essential oil/vinegar/water mixture. Peppermint and nutmeg were only used as a blend rather than as individual oils. Problems of solubility and toxicity are discussed, as are possible mechanisms of action. Phenols, phenolic ethers, ketones, and oxides (1,8-cineole) appear to be the major toxic components of these essential oils when used on lice. Aldehydes and sesquiterpenes may also play a role.
Immunization of rabbits with a faecal extract of the human body louse (Pediculus humanus) induced a high titre of specific IgG. The mean weight of blood taken by females fed on the immunized rabbits was significantly lower (29%) than taken by females fed on the control rabbits. The mean number of eggs per female fed on the immunized rabbits was significantly lower than for females fed on the control rabbits. The hatchability of the eggs laid by lice fed on immunized rabbits (91%) was significantly lower than of those fed on control rabbits (94%). The rate of development of nymphs fed on control rabbits was significantly higher than those fed on the immunized rabbits. There was no difference in survival rates of lice fed on immunized and control rabbits.