Lethality of essential oil constituents towards the human louse, Pediculus humanus, and its eggs

Essential oils have been widely used in traditional medicine for the eradication of lice, including head lice, but due to the variability of their constitution the effects may not be reproducible. In an attempt to assess the contribution of their component monoterpenoids, a range of common individual compounds were tested in in vitro toxicity model against both human lice (Pediculus humanus, an accepted model of head lice lethality) and their eggs, at different concentrations. No detailed study into the relative potencies of their constituent terpenoids has so far been published. Adult lice were observed for lack of response to stimuli over 3 h and the LT(50) calculated, and the percentage of eggs failing to hatch was used to generate ovicidal activity data. A ranking was compiled for adult lice and partially for eggs, enabling structure-activity relationships to be assessed for lethality to both, and showed that, for activity in both life-cycle stages, different structural criteria were required. (+)-Terpinen-4-ol was the most effective compound against adult lice, followed by other mono-oxygenated monocyclic compounds, whereas nerolidol was particularly lethal to eggs, but ineffective against adult lice.     

Ectoparasites of goats in the UK

The goat industry in the UK has expanded rapidly in recent years, but at present there is only a poor understanding of the prevalence of parasitic diseases in this farming system. Here, a questionnaire survey of 110 goat owners was used to address this issue. Problems with louse infestation in the previous 12 months were reported by 23% of owners and 19% reported mange. Chorioptic mange was the most common form, with 14 of 21 cases. Sarcoptic mage accounted for only 3 cases and demodex and psoroptic mange each made up 2 cases. Only 53 farmers (48%) said that they took preventative measures to protect their animals against ectoparasite infestation; 20 of these relied on macrocyclic lactones (MLs), the most common product specified was ivermectin. Therapeutic treatment was used by all respondents who said that they had experienced ectoparasites, and again ivermectin was the most common treatment. The use of fipronil was specified by 3 respondents, including one commercial meat producer. Four farmers said that they used antibiotics as an ectoparasiticide. This pattern of treatment for ectoparasites, with reliance on MLs, has implications for the inadvertent selection of resistance in endoparasites. The results suggest that ectoparasites are a major problem for many goat owners, both commercial and non-commercial, but that there is a need for better information for the goat producing community about the optimum approaches to parasite prevention and treatment.