Increased control of the sheep biting louse Bovicola (Damalinia) ovis with deltamethrin formulated in a fractionated wool grease carrier

The synthetic pyrethroid deltamethrin (DM) containing a trace of [(14)C]-DM was formulated with non-oxidised sterol and wax ester fractions (F1) of wool grease and as the commercial preparation 'Clout-S'. These were applied as a 'backline' strip to sheep immediately after shearing and the concentration of [(14)C]-DM at meridians adjacent to the application strip and at 1/4 and 3/4 of the dorsal-ventral distance was determined. The F1 formulation resulted in significantly greater lateral spread of DM with less remaining at the application site (66+/-8% of dose) 98 days after treatment compared to 'Clout-S' (94+/-3% dose). Autoradiographic examination of treated wool demonstrated that there was more DM in the lower half of the wool staple when formulated in F1 compared to 'Clout-S'. Greater mortality occurred when sheep biting lice Bovicola (Damalinia) ovis were exposed in vitro to wool containing DM from F1 compared to 'Clout-S' treated sheep. In field trials there was increased efficacy against synthetic pyrethroid resistant B. ovis with F1 formulation than with 'Clout-S'. The study has demonstrated that synthetic pyrethroid availability, and therefore efficacy, can be significantly increased when the insecticide is formulated in a 'carrier' with the physicochemical characteristics of wool grease.     

The development of high synthetic pyrethroid resistance in Bovicola (Damalinia) ovis and the implications for resistance management

SUMMARY A field strain of the sheep body louse, Bovicola (Damallnia) ovis, was tested In vitro against a range of synthetic pyrethrolds (SP) and demonstrated a degree of resistance 80 to 900 times that of a susceptible strain. The dose response of this strain was compared with that of other strains showing low and Intermediate resistance. These data, and those from other reported cases suggest that SP resistance In sheep lice develops sequentially through a low level stage with resistance factors of 20 or less. Further selection results in the development of strains with resistance factors of up to several hundred. The implication is that preventing or managing resistance requires proper lice control management Including choosing a chemical capable of eradicating lice populations.     

Evaluation of ear tags impregnated with cypermethrin for the control of sheep body lice (Damalinia ovis)

The application of polymer matrix ear tags impregnated with 8.5% w/w cypermethrin to 6 wethers following shearing reduced lice to non-detectable levels on 4 of them at 29 weeks after tagging. At the conclusion of the study at 45 weeks the mean count of lice on tagged wethers was 3 per sheep compared to 158 on untreated wethers. In a second experiment, 6 non-infected sheep were treated at shearing with cypermethrin tags, 6 with 25 g/l cypermethrin backline formulation, 6 with tags plus backline and 6 were left untreated. Each group was exposed to 6 sheep with moderate to heavy infestations of lice. Compared to controls, all treatments delayed infestation, but cypermethrin tags gave no longer protection than backline treatment. All sheep were infested by 17 weeks after commencement of the study. At 45 weeks mean counts of lice were 38, 27, 20 and 74 respectively for sheep treated with tags, backline formulation, backline plus tags and untreated. Possible reasons for the better effect observed from applying tags to infested sheep than to sheep which were not infected at application but which were subsequently exposed to infested sheep are discussed.     

Effect of insecticidal ear tags on populations of lice (Damalinia ovis) infesting sheep

Polymer matrix ear tags containing 13.7% w/w tetrachlorvinphos or 8.5% w/w cypermethrin were applied to Merino wethers infested with lice and carrying two months wool. The cypermethrin tags reduced louse numbers by a maximum of 89% in comparison to controls at 16 weeks after treatment and by 85% at the conclusion of the experiment 38 weeks after application. Lice were not eradicated from any sheep. The number of lice counted on sheep treated with tetrachlorvinphos-impregnated tags was not significantly different from controls.     

Evaluation of strategies for control of sheep lice (Damalinia ovis) with an epidemiological model

A model was constructed to integrate the epidemiology and economics of control of sheep lice in Victoria and provide an objective basis for comparing lice control strategies. The strategies evaluated included different allocations of Department of Agriculture and Rural Affairs (DARA) resources for detection and supervision of infected flocks and for extension to enhance owner detection rates, change treatment practices or promote the adoption of disease prevention measures. Changes in prevalence and the net present cost of sheep lice to the industry were calculated over a 10-year period. The model predicted that the most profitable lice control strategy was to discourage routine annual treatment, promote treatment on detection, and encourage the adoption of lice prevention measures. The number of infested flocks undertaking eradication programs under DARA supervision had little effect on the prevalence or net cost of lice to Victoria.     

Feeding of the chewing louse Damalinia ovis (Schrank) (Phthiraptera:Trichodectidae) on sheep

The possibility that Damalinia ovis ingests intact epidermis could explain economically important irritation behaviour by infested sheep. To test this, feeding lice were observed on sheep by hand lens and macrophotography and on light and scanning electron microscope preparations. Aspects of feeding behaviour were described, particularly an epidermal ingestion posture. Louse ingesta were examined in paraffin and frozen sections. Lipid-covered stratum corneum squames were identified in crop, midgut, rectum and faeces. Nucleated keratinocytes from inner epidermal strata were not seen, neither were wool fibres. Vertical frozen sheep skin sections, with feeding lice cryofixed by liquid nitrogen, showed mandibles engaged in the outer stratum corneum of the epidermis. The epidermal origin of some ingesta was confirmed by confirming lice over sheep whose skin was stained with Oil Red O, whose colour was seen in crop, midgut, rectum and faeces of harvested lice. Lipase was found in louse midgut. It was concluded that sebaceous secretions may form an important component of the D. ovis diet. The relative contribution from loose scurf or from stratum corneum squames was not determined. Mechanical stimuli by feeding lice did not seem to be the source of host irritation. The role of sensitising agents in louse brei filtrates was investigated with inconclusive results. Intradermal injections of louse faeces did not elicit a demonstrable response.     

Resistance to synthetic pyrethroid pour-on insecticides in strains of the sheep body louse Bovicola (Damalinia) ovis

Groups of sheep infested with strains of Bovicola (Damalinia) ovis were obtained from flocks either with a history of failure to control lice with synthetic pyrethroid (SP) pour-on insecticides, or from farms where SP compounds were not used. The sheep were treated according to the manufacturer's recommendations with registered "off-shears" SP formulations. All treatments were applied under ideal conditions with doses calculated on an individual body weight basis and applied to the dorsal mid-line from the base of the neck to the butt of the tail. Treated sheep were kept in pens and maintained in separate groups. The pour-on SP treatments significantly reduced the lice population but failed to eliminate the infestation in 7 of 13 experiments in sheep carrying strains of lice with resistance factors of greater than 4 to at least one of the SP compounds. Failures occurred with all three of the SP pour-ons currently registered for lice control in NSW and with both water-based and organic solvent-based formulations.     

Observations on the eradication of Brucella ovis infection from a ram flock

The measures taken to eradicate Brucella ovis infection from a naturally infected flock of 64 rams are described. Lesions of epididymitis were detected in 18 rams, all of which gave either positive or suspicious reactions in the complement fixation test. A further 20 rams gave serological reactions in the complement fixation test. Subsequently, semen was collected from 14 of these 20 rams and B. ovis was cultured from the semen of all 14 rams. Serum samples from two rams failed to react in the complement fixation test. However, they were identified as infected with the aid of an enzyme-linked immunosorbent assay and the subsequent culture of semen samples. It is suggested that, when eradicating B. ovis infection from ram flocks, the enzyme-linked immunosorbent assay be used in addition to both the complement fixation test and the physical examination. Using a combination of tests as described can increase the likehood of an earlier eradication of B. ovis infection.     

Field efficacy of an ivermectin jetting fluid for control of the sheep body louse Bovicola (Damalinia) ovis in New Zealand

The efficacy of an ivermectin jetting fluid against the sheep body louse, Bovicola (Damalinia) ovis, in long-woolled sheep was investigated in three field trials. In all trials, louse populations in hand-jetted sheep were reduced to nondetectable numbers within 2 weeks of treatment. Bv comparison, shorn and unshorn control sheep maintained detectable infestations for the duration of the trials.     

Impact of the botanical insecticide Neem Azal on survival and reproduction of the biting louse Damalinia limbata on angora goats

Secondary metabolites present in the neem tree (Azadirachta indica A. Juss, Meliaceae), exhibit a wide range of biological activities in insects. However, few studies have been undertaken to assess the potential of neem products as insecticides for the control of ectoparasites of domestic animals. This study was undertaken to estimate the efficacy of Neem Azal, an azadirachtin-rich extract of neem seeds, in controlling Damalinia limbata (Phthiraptera) louse infestation of angora goats. The study was conducted on a fibre animal farm situated in Central Italy. Groups of 11-12 goats were treated with Neem Azal at an azadirachtin concentration of 650ppm or 125ppm, with Neguvon or were left untreated. Their louse burden was assessed fortnightly to monthly for 22 weeks. A reduction in louse densities of 76-96% was observed from week 2 to week 18 after treatment with the neem solution containing azadirachtin at a concentration of 650ppm. At the lower test concentration (125ppm) a reduction of 60-92% could be recorded from week 2 to week 14. Neem Azal was found to reduce the survival of both adult and nymph stages of D. limbata and to interfere with oviposition and oogenesis of female lice. A decrease in oviposition was observed in neem exposed female lice and the examination of their ovaries revealed morphological alterations in both vitellogenic and previtellogenic ovarioles at the follicular and germinal level. Since neem compounds target different life stages and physiological processes of D. limbata, the development of insecticide resistance by biting lice exposed to neem-based insecticides appears unlikely. For this reason and for its prolonged activity, which in principle allows angora goats to be protected for a large part of the mohair production cycle, neem-based insecticides may have a potential interest for mohair producing breeders.     

Field efficacy of an ivermectin jetting fluid for control of the sheep body louse Bovicola (Damalinia) ovis in New Zealand

The efficacy of an ivermectin jetting fluid against the sheep body louse, Bovicola (Damalinia) ovis, in long-woolled sheep was investigated in three field trials. In all trials, louse populations in hand-jetted sheep were reduced to non- detectable numbers within 2 weeks of treatment. By comoarison, shorn and unshorn control sheep maintained detectable infestations for the duration of the trials.     

Recent insecticides: Their efficacy as plunge dips against the biting louse,Damalinia ovis,and the ked,Melophagus ovinus,on sheep

Abstract

Extract

At the Wallaceville Animal Research Centre, Thomas (1958 Thomas, P. L. 1958. The control of lice (Damalinia ovis) and keds (Melophagus ovinus) — a comparison of the efficiency of common insecticides. N.Z. Jl agric. Res., 1: 217–223. [Taylor &; Francis Online] , [Google Scholar]) and Greenwood (1964 Greenwood, E. S. 1964. Louse control in sheep — a comparison of seven dipping preparations. N.Z. Jl agric. Res., 7: 382–385. [Taylor &; Francis Online] , [Google Scholar]) have tested a number of insecticides against biting lice and keds on sheep. The present paper reports hitherto unpublished work by Millar (nee Greenwood) up to 1966 and more recent work carried out since her departure.     

The pathology of E. ovis

Abstract

Extract

Sir, — In your September issue, Sutton (3) Sulton, R. H. 1978. N.Z. vet. J., 26: 224–230.  [Google Scholar] suggests that the anaemia of E. ovis infection is due to intravascular haemolysis. The pathology he describes is almost identical to that described by Dacie(l) Dacie, J. V. 1963. The Haemolylic Anaemias, 2nd ed., 382–382. London: Churchill.  [Google Scholar] in autoimmune haemolytic anaemia in man; sheep recently exposed to active E. ovis infection are usually positive to the Coombs test(2) Sheriff, D. 1967. Nature, 215: 101–101.  [Google Scholar] and show spherocytosis; in my experience, haemoglobinuria is rarely, if ever, seen in E. ovis infection but is common in intravascular haemolytic conditions in sheep; and, finally, what appears to be haemoglobinaemia in sheep infected with E. ovis may be due to the rupture of abnormally fragile red cells during, or after, collection of the blood. On this evidence, it seems likely that incomplete antibodies are involved in the red cell destruction that characterises E. ovis infection, and that the process takes place extravascularly, by phagocytosis.     

The acquisition of immunity to Histophilus ovis by sheep in nature

It was demonstrated that skin wound infection with Histophilus ovis elicits an immune response which can protect a ram against a challenge injection of the same organism into its epididymis.     

多拉菌素防治绵羊痒螨病试验

目的　肯定多拉菌素防治绵羊痒螨病的效果 ,为临床应用提供科学依据。方法　试验分 5组 (多拉菌素高、中、低剂量组、伊维菌素对照组及空白对照组 ) ,根据试验前后螨虫寄生数量和临床变化判定疗效。结论　多拉菌素防治绵羊痒螨病效果确实可靠 ,其中以高剂量组和中剂量组最为显著 ,推荐剂量为中剂量组即 2 0 0 μg/kg体重