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((R)), 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 >or= 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.

Can kunzea oil (Kunzea ambigua) control head lice (Pediculus humanus capitis)?

“…Based on the results of this study, there is great potential in KO and that it has already demonstrated efficacy above the 80% mortality threshold suggested (Heukelbach et al 2008). However, while in vitro testing shows great potential, it will be critical that controlled field trials and therapeutic potential of formulated products be assessed (Burkhart and Burkhart, 2001).…”

Ex Vivo Development of Eggs from Head Lice (Pediculus humanus capitis)

“…Standard procedures for testing ovicidal properties of pediculicides are needed for a reliable evaluation of products marketed against head lice infestations [8]. Burkhart et al [10] proposed standard procedures, but relied on eggs obtained from infested individuals.…”

“…The situation in practice is further complicated, as many producers of anti-lice products recommend adjunctive combing and sometimes provide a free lice comb with the product. In addition, commercialized products are not bound by health authorities to meet a minimum level of efficacy [8]. Consequently, health professionals and consumers often cannot determine if effectiveness is due to adulticidal and ovicidal properties of the product, or a result of mechanical removal of adults and eggs by adjunctive combing.…”

“…Andar, Fortaleza CE 60430-140, Brazil; Tel: ++55-85-33668045; Fax: ++55-85-33668050; E-mail: heukelbach@web.de topical compounds [8]. For example, considering the low ovicidal efficacy of many compounds, product leaflets usually recommend a second topical application after 7-10 days.…”

“…Consequently, health professionals and consumers often cannot determine if effectiveness is due to adulticidal and ovicidal properties of the product, or a result of mechanical removal of adults and eggs by adjunctive combing. Thus, there is a clear need for adequately designed and standardized adulticidal and ovicidal ex vivo assays [8][9][10].…”