Deon V. Canyon

In vitro efficacy of over‐the‐counter botanical pediculicides against the head louse Pediculus humanus var capitis based on a stringent standard for mortality assessment

Abstract Infestation of the head louse Pediculus humanus var capitis DeGeer (Phthiraptera: Pediculidae) is an important public health problem in Australia, with up to a third of children infested in some primary schools. Insecticide resistance and inadequate attention to the application instructions of topical pediculicides are common reasons for treatment failure. This study evaluated six popular Australian over‐the‐counter products against head lice, primarily comprised of different botanical extracts, and compared them with permethrin 1% (Quellada®) and a non‐treatment control in order to assess their in vitro efficacy. We also assessed commonly used criteria for evaluating pediculicide efficacy in vitro. All tested products failed to demonstrate high levels of efficacy with the exception of Tea Tree Gel®, which outperformed 1% permethrin. Permethrin had a high level of efficacy, but using stringent criteria 18% of lice were not dead at 3 h, indicating some resistance to Quellada®. Commonly used less stringent criteria were shown to overestimate mortality of head lice as a result of the protective phenomenon of stasis or sham death observed in exposed lice that may recover after some time. Using two different levels of stringency resulted in different rankings of efficacy for most products, with the exception of the first ranked product, Tea Tree Gel®. Rankings of efficacy also varied over time, even within the different assessment criteria. Government regulatory agencies should require standard in vitro tests using stringent mortality criteria, with an observation period of ≥ 6 h, to determine the efficacy of new pediculicides, and only products that cause a minimum mortality rate (e.g. 80%) in head lice collected from the target population should be licensed for sale.

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.

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.

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.

Efficacy of Eight Larvicidal Botanical Extracts from Khaya senegalensis and Daucus carota against Culex annulirostris

ABSTRACT The failure to discover a significant new class of insecticides has led many researchers back to biodiscovery studies in the search for new and economically viable alternatives. After a preliminary screening of botanical extracts using descending series of concentrations (1,000, 500, 100, 50, and 5 mg/liter), 8 extracts from 2 potential botanical agents, Khaya senegalensis (Desrousseaux) and Daucus carota L., were tested against 4th instars of Culex annulirostris (Skuse) following the standard World Health Organization insecticide susceptibility methodology. The median lethal concentration (LC50) values for K. senegalensis against Cx. annulirostris using acetone, ethanol, hexane, and methanol extracts were 20.12, 5.1, 5.08, and 7.62 mg/liter, respectively. The LC50 values for D. carota against Cx. annulirostris using acetone, ethanol, hexane, and methanol extracts were 236.00, 36.59, 77.19, and 241.8 mg/liter, respectively. Extracts from K. senegalensis were more potent than those from D. carota against Cx. annulirostris and hexane and ethanol were the best solvents to extract essential oils from both plant species, respectively. In potency, K. senegalensis was similar to azadirachtin, but fractionation and compound isolation of the hexane extract in particular may reveal a potent phytochemical that could be compared to synthetic mosquitocides.

A mosquito predator survey in Townsville, Australia, and an assessment of Diplonychus sp. and Anisops sp. predatorial capacity against Culex annulirostris mosquito immatures

ABSTRACT A twelve-month survey for mosquito predators was conducted in Townsville, Queensland, Australia, which is located in the arid tropics. The survey revealed the presence of five predaceous insects but only Anisops sp. (backswimmers) and Diplonychus sp. were common. Predatorial capacity and factors influencing this capacity were then assessed for adult Anisops sp. and adult and nymph stages of Diplonychus sp. against Culex annulirostris mosquito immatures under laboratory conditions. Predatorial capacity bioassays showed that adult Diplonychus sp. preyed upon both larval and pupal stages of Cx. annulirostris quite successfully. Nymphs of Diplonychus sp. proved to be more successful with smaller prey immatures, and Anisops sp adults did not prey successfully on any prey pupae. Increasing the foraging area and introducing aquatic vegetation significantly reduced the predatorial capacity of Diplonychus sp. nymphs, while only vegetation and not foraging area had a significant effect on adult Diplonychus sp. predation capacity. Overall, adult Diplonychus sp. proved to be a more efficient predator than Anisops sp., and field trials are now recommended to further assess the potential of Diplonychus sp. as a biocontrol agent.

Uncovering Family Experiences with Head Lice: The Difficulties of Eradication

Head lice (Pediculus humanus capitis) are not a significant public health concern but elicit great alarm among parents. The investigators host information websites through which they field several hundred queries annually. This study investigated the experience of those treating head lice infections focusing on control difficulties. A short web-based questionnaire (available August, 2006 and February, 2007) yielded two hundred and ninety-four eligible responses which were analysed using grounded theory analysis processes. The mainly female (91.1%), working (76.9%), respondents from Australia, U.S.A., Canada and UK identified constraints for effective treatment that encompass technological, biological and social issues. Product concerns, treating children and blaming others for re-infection were among the main themes. Available treatment technologies are incompatible with the lifestyles of families in developed market economies. The treatment methodology, nit comb and topically applied liquid, is several thousand years old. Future research and devel- opment efforts need to account for the social constraints experienced by lay consumers.

Do head lice spread in swimming pools

This study investigated the potential for head lice transmission in swimming pools using an in vitro experiment and a field trial. In the former study, head lice were submerged for 20 min in aqueous solutions at 25 ± 1 °C: deionized water, sea water, salt solutions (30, 60, 120 and 240 g/l), and chlorinated water (0.2, 2 and 5 mg/l). In all trials, lice located on cut hairs became immobile and did not respond to physical prodding. After entering stasis, no movement was observed until after rescue from submersion and a brief recovery period (0–1 min). Upon recovery, all lice fed and no mortality was observed within the next 4 h. In the field trial, four naturally infected individuals swam in a chlorinated pool for 30 min. No loss of lice or head to head transfer was observed. These results indicated that although head lice survive immersion, head lice transmission is unlikely to occur via the water of swimming pools.

Indirect Transmission of Head Lice via Inanimate Objects

Whether people can become infected by head lice transferring from inanimate objects is a topic of controversy. This paper reviews the evidence available from experimental studies in controlled laboratory experiments and data from field studies. The weight of evidence appears to be against transmission from inanimate objects being significant, and the promotion of inanimate objects that play an epidemiologically important role in head lice dispersal is not supported by evidence. We conclude that the control of head lice should focus on the head, not on the environment. However, additional studies are needed to quantify transmission risk via inanimate objects and the probability that head lice eggs survive and hatch off-host.

Head lice: the feelings people have

Background  Head lice are a source of amusement for outsiders and an embarrassing nuisance to those who have to deal with them. Our study collected the emotions experienced by people dealing with head lice. An area with extremely sparse literature, our purpose is to inform the development of more effective programs to control head lice.