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.     

Temporal relationship between infestation with lice (Bovicola ovis Schrank) and the development of pruritic behaviour and fleece derangement in sheep

Pruritic behaviour and deranged fleece are often used as indicators of sheep louse infestation but the exact relationship between infestation and the observation of signs of pruritis was unclear. Two studies were conducted to examine this association. In the first, 24 castrate Merino sheep were randomly assigned to six pens in groups of four and the sheep in three pens infested with 10 lice each on the right mid-side. Louse numbers were counted, fleece derangement scored and pruritic behaviour assessed periodically on each sheep until 38 weeks after infestation. In the second study a single moderately infested sheep was paddocked for 15 weeks with 32 uninfested sheep and louse numbers and fleece derangement monitored for 41 weeks. In the pen studies, differences between infested and non-infested sheep in fleece derangement and pruritic behaviour first became significant (p<0.05) at 8 and 14 weeks, respectively and at louse densities of 0.06 and 0.27 per 10 cm wool part. Some sheep showed definite signs of deranged fleece as early as 5 weeks after initial infestation. In the paddock studies, it took 37 weeks until lice were detected on all sheep in the flock. The correlation between louse numbers and fleece derangement score first became significant (r=0.44 and p<0.05) at 9 weeks after introduction of the lousy sheep, reached a maximum of r=0.79 (p<0.001) at 22 weeks when 84% of sheep had lice detected and the mean louse density was 0.29 per part, and then declined to r=0.12 (n.s.) at 41 weeks when all sheep were infested and the mean louse density was 3.04 per part. It is concluded that fleece derangement is a powerful early indicator of the presence of lice and that sheep may exhibit signs of pruritis well before lice can be readily found by direct inspection. Fleece derangement may be useful as a basis for establishing economic thresholds for the application of long wool treatments in developing louse infestations but appears to be a poor indicator of louse numbers once the infestation is advanced.     

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.     

Some currently available insecticides and their comparative efficacy on louse-infested, long-woolled sheep

The comparative efficacy of 13 of the sheep dips currently registered in New Zealand was investigated using sheep infested with the louse Bovicola ovis and carrying wool which was about 10 cm long at the shoulder. With the exception of one synthetic pyrethroid pour-on formulation, all products were able to effect a significant reduction in louse populations, relative to untreated controls, for 37 days after treatment. Only four products proved capable of eradicating lice and preventing their re-establishment up to 37 days after treatment. Variations in manufacturers' recommendations relating to the length of wool at dipping, and mode of application of dips are discussed in relation to the results.     

Variation among Merino sheep in susceptibilty to lice (Bovicola ovis) and association with susceptibility to trichostrongylid gastrointestinal parasites.

Sheep of two bloodlines of Merino were artificially infested with equal numbers of lice (Bovicola ovis) and the resulting louse populations were monitored over the following 20 months. The sheep were shorn 6 and 17 months after infestation and, for analysis, the louse counts considered in 3 years separated by shearings. Nematode faecal egg counts (FECs) were assessed on faecal samples collected on five occasions, three times following natural challenge and twice after artificial challenge with 40,000 trichostrongyloid larvae (84% Trichostrongylus vitrinus). In addition, blood samples were collected and measured for B. ovis-specific immunoglobulins (predominantly IgG), B. ovis-specific IgE and serum total IgE. Bloodlines differed significantly in the size of louse populations at the end of year 2, FEC after both natural and artificial challenge and in serum levels of all three antibodies (p<0.05). There were also large variations in louse counts and FEC among sheep within bloodlines. Louse counts at inspections after louse populations had been allowed to build up were highly repeatable, both between and within years. However, correlations with counts at inspections soon after initial infestation and following shearing were lower. FEC after natural challenge was correlated with louse counts in year 2 (r=0.45, p<0.01) and year 3 (r=0.38, p<0.05), but the correlation with counts in year 1 was not significant (r=0.25, p>0.05). FEC following artificial challenge was significantly correlated with louse counts in year 3 (r=0.36, p<0.05), but not in year 2 (r=0.25, p>0.05) or year 1 (r=0.04, p>0.05). Louse counts in the 3 years were significantly correlated with anti-B. ovis antibody concentration (r=0.60, 0.48, 0.36), but not with levels of either anti-B. ovis or total serum IgE.These results suggest that sheep with greater resistance to gastrointestinal parasites also tend to be less susceptible to lice. Whether this is due to interaction of the effects of the parasites or to correlation in underlying resistance mechanisms requires clarification.     

The comparative ability of some lousicides to reduce cockle in sheep pelts

Sheep naturally infested with the biting louse, Bovicola ovis were treated with a range of organophosphorus and synthetic pyrethroid dip formulations. The sheep were killed 42 days after treatment and the pelts examined for evidence of cockle, a nodular condition that appears in some sheep as a response to the presence of lice. Sheep treated to saturation with dip formulations produced more high quality pelts than did sheep treated with low volume, pour-on or spray-on dips. These differences are suspected to arise because louse populations decline more slowly after treatment with pour-ons or spray-ons than with saturation dips. The removal of lice and regression of cockle resulted in a high percentage of first grade pickled pelts. However, processing through to the dyed crust leather stage highlighted lesions in the same pelts that were not apparent at the pickle stage and lead to a substantial increase in the number of downgraded pelts.     

Assessment on major factors that cause skin rejection at Modjo export tannery,Ethiopia

A study was conducted from November 2009 to March 2010 with the objective of identifying the major causes of skin rejection on fresh, pickled, and wet blue skins at Modjo Mesaco Global tannery. A total of 401 fresh and 1,873 pickled and wet blue skins from the routine production system of the tannery were used. Overall, high prevalence of sheep ked (100%) followed by biting louse (64.4%), tick (50%), and sucking louse (45.8%) were observed on fresh sheep pelts, while, on fresh goat pelts, a high prevalence of sucking louse (54.5%), followed by tick (50%), and biting louse (35.5%) were observed. From the total of 90 rejected pickled and wet blue skins of sheep and goats, 98.8% were “ekek” and scratch, 85.6% sheep and goat pox, 74% poor substance, 73.3% heat, 72.2% scar, and 52.2% knife cut-in skins. Large number of skins rejections was recorded in large-sized skins (29.8%), and the lowest observed was in medium-sized skins (11.1%). There were highly statistically significant association (p < 0.05) between size and grades of shoat skins. Ekek and scratches together with sheep and goat pox were the common skin defects that hamper skin quality. However, there was no significant association (p > 0.05) between sheep and goat skins. Ekek and scratch caused high rejection of skin and entailed serious economic loss in terms of foreign exchange earning to Ethiopia. Therefore, the main causes of skin rejection and factors that cause downgrading of skin should be controlled.     

Sensitivity of two-stage sampling to detect sheep biting lice (Bovicola ovis) in infested flocks.

The sampling distribution of Bovicola ovis (Schrank) on sheep was examined in two flocks, one with a light and one with a heavy infestation of lice. The derived distributions were used to calculate the sensitivity of detecting lice on individual sheep and in flocks by fleece parting regimes that varied in number of parts per animal and number of sheep per flock, different scenarios of flock sizes, proportion infested and louse density were examined. Lice were aggregated among fleece partings in the heavily infested flock and described by a negative binomial distribution with k values between 0.3 and 1.92. The distribution was indistinguishable from Poisson in the lightly infested flock. The assumed distribution had little effect on sensitivity, except when only one fleece part per animal was examined. On individual sheep where louse density was 0.5 per 10 cm part or greater, there were only marginal gains from inspecting more than 10 parts per animal. Increasing the number of sheep inspected always increased sensitivity more than increasing number of parts per sheep by an equivalent amount. This advantage was greatest in situations where a low proportion of sheep in the flock were infested with a high density of lice, and less where a low proportion of sheep were infested with a low density of lice, or a high proportion of sheep were infested with a high density of lice.     

Dual deficiency of copper and cobalt in Hawke's Bay

The comparative efficacy of 13 of the sheep dips currently registered in New Zealand was investigated using sheep infested with the louse Bovicola ovis and carrying wool which was about 10 cm long at the shoulder.

With the exception of one synthetic pyrethroid “pour-on” formulation, all products were able to effect a significant reduction in louse populations, relative to untreated controls, for 37 days after treatment. Only four products proved capable of “eradicating” lice and preventing their re-establishment up to 37 days after treatment.

Variations in manufacturers' recommendations relating to the length of wool at dipping, and mode of application of dips are discussed in relation to the results.     

Prevalence and clustering of louse infestation in Queensland sheep flocks.

Information provided by wool growers in Queensland, Australia between 1995 and 1997 was used to assess the prevalence and spatial distribution of louse (Bovicola ovis) infestation in sheep flocks. The estimated prevalence of louse-infested flocks was 40% (95% confidence interval, 35-46%). Although the prevalence of infestation was higher in western regions (41-50%) compared to the south region of Queensland (31%), the difference was not statistically significant (P > 0.05). Significant (P = 0.02) clustering of infested flocks was detected in the south region where two foci were apparent. We conclude that Queensland sheep flocks have a moderate prevalence of louse infestation, and that clustering of infestation is not strong. The control of lice is an industry-wide issue that needs to be addressed by most wool growers in Queensland.     

Treatment of natural infestations of the biting louse (Werneckiella equi) on horses using triflumuron, a benzoylurea derivative insect growth regulator

The horse biting louse (Werneckiella equi) is a common global equine ectoparasite. To our knowledge, benzoyl(phenyl)urea insecticides (triflumuron, diflubenzuron) commonly used as sheep lousicides, have not been evaluated for efficacy against W. equi. The aim of this study was to determine louse control efficacy, general wellness and dermal safety following triflumuron application as a backline pour-on to horses. Two efficacy trials using 25 adult naturally infested lousy horses, and a dermal safety trial using 10 adult louse-free horses were conducted over a 14-month period. Lousy animals were selected by assessment of their lice status prior to treatment. For the efficacy trial, the triflumuron product was applied at a dose of 2.5mg triflumuron per kg bodyweight (1 mL product per 10 kg bodyweight). For the safety study, triflumuron was applied at a 3x clinical dose of 7.5 mg triflumuron per kg bodyweight (3 mL product per 10 kg bodyweight). In our first efficacy trial, 100% lousicidal efficacy was achieved by day 44 post-treatment. In our second trial, no lice were identified on horses by day 71 post-treatment. In the safety trial, no adverse effects were seen. Results of this study demonstrate that the off-label, experimental pour-on application of triflumuron at 2.5 mg/kg bodyweight is convenient, highly effective and safe (at 3x the clinical dose) for the treatment of the horse biting louse, W. equi.     

Spatial distribution and spread of sheep biting lice, Bovicola ovis, from point infestations

The spatial distribution of chewing lice (Bovicola ovis) on their hosts was examined in Polypay and Columbia ewes initially artificially infested on the midside or the neck. Densities of lice were determined at 69 body sites in eight body regions at approximately monthly intervals for 2 years. In the second year, half of the ewes were mated and lice were counted at 26 body sites on the resulting lambs. Polypay ewes had higher densities of lice than Columbias at most inspections but there was little effect of infestation point or mating on either numbers or the distribution of lice. During periods of high louse numbers densities were generally greatest on the sides or the back. Densities on the head were also high at times and peaked later than overall louse densities. Shearing markedly reduced density but increased the proportion of lice found on the neck, belly and lowleg sites. The distribution of lice on the lambs was similar to that on the ewes except that fewer lice were found on the head. Comparisons of lice per part with the numbers of lice extracted from clipped patches indicated that a sheep with wool bearing area of 1 m2 and a mean count of one louse per 10 cm fleece parting carried approximately 2000 lice. At most times of the year inspections for sheep lice should be concentrated on the sides and back, but in recently shorn sheep greater attention should be paid to the lower neck and ventral regions. Implications of the observed distributions of lice for the efficacy of chemical treatments are discussed.     

Propetamphos pour-on formulation for the control of lice on sheep: effect of lice on weight gain and wool production

Infestation of sheep with the biting louse Damalinia ovis is a potentially serious problem which can effect the quality and quantity of wool produced and may reduce weight gains. In this trial treated sheep produced 34 per cent more wool than louse-infested controls and the wool from the treated sheep was of a better quality. The mean liveweight gain in the treated groups was 18 per cent more than that in the untreated group. Treatment with a pour-on formulation of propetamphos at 25 to 50 mg kg-1 gave more than 99 per cent control of lice and protected against reinfestation for four months.     

Dipping and jetting with tea tree (Melaleuca alternifolia) oil formulations control lice (Bovicola ovis) on sheep

The in vivo pediculicidal effectiveness of 1% and 2% formulations of tea tree (Melaleuca alternifolia) oil (TTO) against sheep chewing lice (Bovicola ovis) was tested in two pen studies. Immersion dipping of sheep shorn two weeks before treatment in both 1% and 2% formulations reduced lice to non detectable levels. No lice were found on any of the treated sheep despite careful inspection of at least 40 fleece partings per animal at 2, 6, 12 and 20 weeks after treatment. In the untreated sheep louse numbers increased from a mean (±SE) of 2.4 (±0.7) per 10cm fleece part at 2 weeks to 12.3 (±4.2) per part at 20 weeks. Treatment of sheep with 6 months wool by jetting (high pressure spraying into the fleece) reduced louse numbers by 94% in comparison to controls at two weeks after treatment with both 1% and 2% TTO formulations. At 6 and 12 weeks after treatment reductions were 94% and 91% respectively with the 1% formulation and 78% and 84% respectively with the 2% formulation. TTO treatment also appeared to reduce wool damage in infested sheep. Laboratory studies indicated that tea tree oil 'stripped' from solution with a progressive reduction in concentration as well as volume as more wool was dipped, indicating that reinforcement of active ingredient would be required to maintain effectiveness when large numbers of sheep are treated. The results of these studies suggest significant potential for the development of ovine lousicides incorporating TTO.     

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.     

Inspection of wool lots at sales as a diagnostic test for louse infestation

The accuracy of visual inspection of wool lots for lice as a test for louse infestation was estimated using information provided by 178 woolgrowers in Queensland, Australia. The estimated sensitivity of inspection was 36% (95% confidence interval, 19-58%) and the specificity was 95% (95% CI, 88-98%). Accuracy was influenced by timing, after shearing, of pesticide application for louse control and by class of pesticide last applied after shearing. Visual inspection was less sensitive (29%) if pesticides were applied >3 months after shearing and less sensitive (21%) if an insect growth regulator was the class of pesticide last used after shearing. Based on 36% sensitivity, it was estimated that 16 inspections would have to be conducted to reduce the false negative test rate to <20% in the study population. We suggest that visual inspection of wool lots could be used to efficiently monitor the prevalence of louse infestations in Queensland sheep flocks. Positive inspection results are more likely to represent real louse infestations, rather than a false test result, in flocks grazed in the more extensive regions of Queensland.     

The efficacy of formulations of triclabendazole and ivermectin in combination against liver fluke (Fasciola hepatica) and gastro-intestinal nematodes in cattle and sheep and sucking lice species in cattle

OBJECTIVE: To assess the efficacy of two formulations of triclabendazole and ivermectin in combination against liver fluke (Fasciola hepatica), gastro-intestinal nematodes and sucking louse species in cattle and sheep. PROCEDURE: A study of 540 cattle and 428 sheep at 18 sites throughout Victoria and New South Wales was undertaken. At each site, one group of cattle or sheep was treated with a combined formulation (Fasimec Cattle or Fasimec Sheep), another received ivermectin and triclabendazole separately. In trials on lice infestation, an additional group remained untreated. Samples for faecal egg counts were collected on days -7, 0 (treatment day), +7, +14 and +21 after treatment. Lice assessments were carried out on days -7, 0, +7, +14, +28, +42 and +56. RESULTS: Both treatments were highly efficacious (> 98% efficacy) against liver fluke in cattle and sheep, against three sucking lice species of cattle and against gastro-intestinal nematodes in sheep. There was also no significant difference between treatments in efficacy. Against gastro-intestinal nematodes, Fasimec Cattle was significantly (P < 0.01) more effective than the separately applied ivermectin and triclabendazole treatment. Mean efficacy for the Fasimec Cattle and Ivomec/Fasinex 120 groups respectively, was 97.6% and 94.2% on Day +7, 98.9% and 91% on Day +14 and 98.5% and 92.6% on Day +21. CONCLUSION: The efficacy of Fasimec' Cattle and Fasimec Sheep was at least equal to that of currently registered products (with the same active ingredients) used to control these parasites.     

The prevalence of itchmite, Psorergates ovis, among sheep flocks with a history of fleece derangement

An investigation of sheep flocks in the main sheep raising areas of New South Wales showed that the itchmite Psorergates ovis was frequently associated with fleece derangement. In 26 of the 41 flocks examined, P. ovis was the only ectoparasite detected. P. ovis and the sheep body louse Damalinia ovis, were found in 5 flocks. No external parasites were found on sheep examined from the 10 remaining flocks. The type of fleece derangement most frequently recorded was rubbing which in some cases was combined with areas of chewed fleece. Among flocks, there were positive relations between the prevalence of fleece derangement and prevalence of itchmite or scurf and between itchmite count and mean scurf score. Within flocks, itchmite infested sheep or sheep with scurf had higher prevalences of fleece derangement than sheep on which no mites or no scurf were found. Itchmite infested sheep had a higher prevalence of scurf than those with no detectable mite infestation. There were no significant differences in itchmite populations or fleece derangement between untreated flocks and flocks treated with synthetic pyrethroids, organophosphates or arsenic and rotenone.     

Determinants influencing prevalence of louse infestations on layers of district Faisalabad (Pakistan)

1. This paper describes the influence of some epidemiological determinants on the prevalence of louse infestation on layers in Faisalabad (Pakistan). 2. Seventy layer farms were screened to determine the prevalence of louse infestation and its determinants including age of the bird, availability of space per bird and frequency of litter change. Prevalence of Lipeurus caponis was highest (53.2%), followed by Menacanthus stramineus (22.16%), Goniodes dissimilis (12.37%) and Goniodes gallinae (12.37%). 3. Older birds (36 to 74 weeks of age) were found with a significantly higher prevalence of louse infestation than younger birds. 4. Month-wise prevalence of louse infestation was higher during the summer months (from April to August) and at older age. 5. Birds kept at floor area allowances ranging from 0.43 to 0.55 m(2) were highly infested with lice as compared to those provided with a space of 0.61 m(2) or higher per bird. 6. Litter change frequency after every 8 weeks resulted in a reduced chance of louse infestation as compared to less frequent litter changing practice. 7. It was concluded from the study that the louse infestation is a menace for the poultry production industry in Pakistan and age, space per bird and litter change frequency are the influencing determinants. 8. Further research on the chemotherapeutic trials and resistance in poultry should be continued for an effective lice control program.     

Pesticide use and residues on Queensland wool

Objective To determine practices for control of louse infestation and blowfly strike in Queensland sheep flocks that are associated with organophosphorous and synthetic pyrethroid residues on wool.
Design Information on residues was obtained from a survey of Queensland wool clips. Information on pesticide use was obtained from a trace-back postal survey. The association between pesticide use and residues was assessed using generalised linear models, controlling for potential confounding by flock location.
Procedure Between 1995 and 1997 Queensland wool clips were randomly sampled. Samples were tested for the presence and amount (mg per kg of greasy wool) of organophosphorous and synthetic pyrethroid pesticides. A questionnaire seeking information on flock characteristics and pesticide use was sent to the manager of each flock from which a wool sample was tested.
Results The median amount of OP and SP residue was 0.8 and 0.25 mg/kg, respectively, and 91 and 95% of wool samples contained < 8 mg/kg of OP and SP residues, respectively. The frequency of OP pesticide use for louse control was significantly (P = 0.005) associated with mean OP residue amount, and the timing of SP use for louse control, in relation to shearing, was significantly (P < 0.001) associated with mean SP residue amount.
Conclusion Most Queensland wool clips have acceptable amounts of residues after the use of OP and SP pesticides, but wool growers can further reduce residues by effectively controlling louse infestation with pesticide applications early after shearing and the use of non-chemical methods of ectoparasite control.