Biochemical studies on sheep body louse Bovicola ovis (Schrank) (Phthiraptera: Trichodectidae): comparison of pyrethroid and organophosphate resistant and susceptible strains

Strains of sheep louse Bovicola ovis (Schrank) with various levels of resistance to pyrethroid and one strain with high degree of resistance to organophosphate (OP) insecticides were used to investigate the biochemical mechanisms of insecticide resistance, i.e., enhanced levels of general esterases, specific acetylcholinesterases (AChE), glutathione S-transferase (GST), and mixed function oxidases. Native gel electrophoresis combined with quantitative enzyme assays showed analogous expression profiles of several esterase isozymes in all the strains tested. The determination of the sensitivity of each esterase isozyme to five inhibitors (acetylthiocholine iodide, butyrylthiocholine iodide, paraoxon eserine sulfate, and pCMB) led to the identification of nine esterases in the B. ovis strain. Gel electrophoresis results are supported by enzyme assay studies where, except for the OP resistant strain, no differences in esterase activities were detected in all the pyrethroid resistant and susceptible strains assayed. Statistical analyses demonstrated that some strains have elevated GST activities compared to the susceptible reference strain.     

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.     

Ectoparasites: future challenges in a changing world

Ectoparasites are ubiquitous, often highly damaging and in most cases cannot be permanently eradicated; hence, they must usually be managed at a local scale with insecticides or endectocides. However, the growth in resistance, the slow rate of development of new actives, coupled with environmental and health concerns associated with the continued use of some of the existing neurotoxic insecticides, suggest that more sophisticated approaches to their management need to be identified. These approaches need to allow ectoparasite populations to be maintained at acceptable levels, while conserving the compounds that remain available. The development of integrated approaches, in which cascades of management tactics are deployed, with parasiticides available as one component to be used in requisite circumstances, may be the most appropriate route to achieving this aim. An essential element of such an approach is the clear articulation of the purpose of intervention and rational justification of the time-point and manner in which it is attempted. However, for this to be possible, considerably better information is required about the effects of ectoparasite abundance on animal welfare and productivity, in addition to the greater availability of effective alternative control tools. To this end, recent work undertaken at the School of Biological Sciences at the University of Bristol, into the use of biological control agents, off-host trapping and the selective treatment of more highly susceptible individuals or classes of host, is reviewed here.     

An investigation and comparison of the bioactivity of selected essential oils on human lice and house dust mites

The insecticidal potency of some essential oils suggests that they may find an application in the control of house dust mites, but current in vitro assays for mites do not appear to give consistent results. A simple, novel, mite chamber assay was therefore developed to carry out testing. Different species of insects are susceptible to different essential oil components, so we compared the relative acaricidal and pediculicidal activity of three essential oils: tea tree, lavender and lemon, because the activity of their constituents on lice ranges from highly active to virtually inactive. The most effective essential oil against both lice and mites was tea tree oil; lavender was the second most effective, and lemon oil the least, although it did show activity against mites, unlike lice. The assay proved simple and effective and gave reproducible results.     

Genetic aspects of sheep parasitic diseases

There is evidence of genetically determined host resistance mechanisms for most of the sheep parasites evaluated. The mechanisms vary; from no or reduced establishment, early expulsion, to suppression of parasites resulting in reduced size and fecundity. There is a need to integrate breeding for parasite resistance with the genetic improvement of production traits in farm animals, aiming for optimum solutions for potentially conflicting responses. Sustainable parasite control must be based on Integrated Parasite Management utilising an interdisciplinary approach.     

Variation in sea lice infestation on Atlantic salmon smolts in Killary Harbour,West Coast of Ireland

Approximately 300 salmon smolts were stocked in each of four cages moored at various distances between an Atlantic salmon farm and a river system in Killary Harbour on the West Coast of Ireland. Samples of fish were taken from each of the cages on three occasions and examined for the presence of sea lice (Lepeophtheirus salmonis). Results from one-way ANOVA tests and a multiple comparison of the means of infection levels in the cages indicated that there was a significant difference between the infection levels in the cages on each of the sampling dates. Cage 1, positioned nearest the river, exhibited the highest levels of infection on the first sampling date and was highly significantly different (p 0.001) from the other three cages which showed no significant difference between each other. This situation was again repeated on the second sampling date. On the final sampling date, cage 4, positioned nearest the salmon farm, was highly significantly different (p 0.001) from the other three cages; cage 1 was significantly different (p 0.05) from cages 2 and 3 which showed no significant difference from each other.The population structure of the lice recovered from the smolts indicated that the lice settled in pulses rather than continuously over the trial period. The results are discussed in relation to the hydrography of Killary Harbour, the output of lice larvae from the farm, the impact that these may have on infestations in the inner area of Killary and probable areas of lice larval production.