Hypersensitivity skin testing of lambs infested with the biting louse (Bovicola ovis)

Abstract Cockle, a defect of lamb's pelts, has recently been shown to be associated with infestation of lambs with the louse Bovicoh ovis. The mechanisms by which infestation with the louse leads to cockle are not known, but immunological hypersensitivity has been suggested. The objectives of our work are to determine if lambs respond immunologically to lice and, if so, whether hypersensitivity occurs. Preliminary results are presented here.     

An improved drench for the treatment of the tapeworm,Moniezia expansa,in sheep

Extract

The treatment of sheep specifically for tapeworm infestation has generally not been advocated, most authorities maintaining that Moniezia expansa is rarely pathogenic when not associated with concurrent nematode infestations. Most sheep develop a good immunity to these parasites which are usually expelled within three months of the host contracting the infestation. On the other hand, there are numerous scattered references to loss of condition and occasionally to deaths attributed to Moniezia infestation in lambs.     

Linognathus weisseri n. sp. (Phthiraptera: Linognathidae) of impalas, Aepyceros melampus: description and biology

The adult male and female and first instar nymph of the sucking louse Linognathus weisseri n. sp. are described. This louse was collected from impalas, Aepyceros melampus, at three localities in Limpopo Province, and at three in Mpumalanga Province, South Africa. Although it usually accounted for only a small proportion of the total louse burden, its overall prevalence exceeded 27%. Its prevalence on adult male impalas (9%) was significantly lower (P = 0.004) than that on adult females (39%), but did not differ among age classes. However, the intensity of L. weisseri infestation was higher on lambs than on yearlings and adults, and peaked on impalas in late winter to early summer. Five species of lice are now known to parasitize impalas and a key for distinguishing adults of these species is included.     

The distribution of Nematodirus spp. occurring in sheep in New Zealand

Extract

Most outbreaks of parasitic gastro-enteritis in sheep in New Zealand have been ascribed to the presence of nematodes of the family Trichostrongylidae, and in particular the genera, Haemonchus, Ostertagia, and Trichostrongylus. However, during the period 1956–58, a number of outbreaks of disease occurred in lambs and the condition was associated with heavy Neniatodirus infestation. Although Neinatodirus spp. are commonly foundin sheep in this country, only moderate numbers of worms are usually present in any individual and the worm has been regarded as non-pathogenic. Similar views were held in the British Isles until about 1951, when an acute disease condition of lambs, associated with heavy Neniatodirus burdens, caused serious losses.     

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.     

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.     

Prevalence and regional distribution of scab, lice and blowfly strike in Great Britain

The prevalence of psoroptic mange (sheep scab), louse infestation and blowfly strike in sheep in Great Britain between March 2003 and February 2004 was investigated by means of a retrospective postal survey, stratified by region. Of the 3530 questionnaires sent out, 1067 were returned completed, a response rate of 30.2 per cent. Overall, 9 per cent of the farmers reported at least one outbreak of scab, 10.7 per cent reported an outbreak of lice and 75 per cent reported at least one case of blowfly strike. A mean of 1.4 per cent of ewes were struck by blowfly and 2.8 per cent of lambs. There were strong regional variations in disease prevalence, with scab and lice infestation being highest in Wales, Scotland and the north of England and blowfly strike highest in the south west of England.     

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.     

Ixodid ticks of impala (Aepyceros melampus) in Swaziland: effect of age class,sex, body condition and management

Five species of ixodid ticks, Amhlyomma hebraeum, Boophilus decoloratus, Rhipicephalus appendiculatus, R. evertsi evertsi and R. muehlensi, were commonly collected from impala (Aepyceros melampus) in the Mlawula-Mbuluzi-Simunye Nature Reserve and Protected Area complex in north-eastern Swaziland. The prevalence and apparent intensity of infestation of most tick species was greater on yearlings (13-24 months of age) and adults (> 24 months) than on lambs (≤12 months), and on adult males than on adult females. The packed cell volume and marrow dry weight were lower in impala infested with A. hebraeum, and in lambs and adults with moderate to heavy loads of R. muehlensi and/or R. appendiculatus. The age and sex patterns of tick infestation were probably determined by both body condition and host behaviour. The prevalence and apparent intensity of infestation of most tick species was greater in the unmanaged, densely populated area of the reserve than in the managed area from which impala had been culled. This trend was consistent in all months, and in all age classes.     

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.     

Mortality in calves, lambs and kids caused by severe infestation with the cat flea Ctenocephalides felis felis (Bouché, 1835) in Israel

Heavy infestation of calves, lambs and kids with the cat flea Ctenocephalides felis felis (Bouché, 1835), accompanied by severe anaemia and mortality, is described. Lambs and kids were affected more severely than calves. Flea infestation was more widespread in summer and autumn than in winter and spring. The clinical findings are discussed in the light of the pertinent literature.     

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.     

Prevalence of sucking and chewing lice on cattle entering feedlots in southern Alberta

Beef calves from 2 sources entering southern Alberta feedlots in the winters of 1997-98 and 1998-99, were surveyed for the presence of lice. A random sample of multiple source (MS), that is, auction market-derived, calves entering commercial feedlots and single source (SS) calves entering a backgrounding feedlot were examined for the presence of lice at entry to the feedlot. A standardized examination, which involved hair-part examination of 8 louse predilection sites, was conducted on each selected calf to determine prevalence and intensity of infestation. The long-nosed sucking louse, Linognathus vituli, was the most commonly encountered species. This species infested from 57.8% to 95.6% of the calves selected from both MS and SS calves during both winters. Louse index values, indicating intensity of infestation, for L. vituli ranged from 1 to 243 lice per animal. The chewing louse, Bovicola bovis, was present on MS and SS calves only in the winter of 1998-99. The louse index values for B. bovis ranged from 1 to 230 lice per animal. Mixed infestations of the L. vituli and B. bovis were common. The little blue cattle louse, Solenopotes capillatus, was present only on the SS calves in the winter of 1997-98. The short-nosed sucking louse, Haematopinus eurysternus, was present at very low intensities, 1-2 lice per animal, on 2.6% to 4.4% of the MS calves during both winters. Comparison of results from the current study with published literature suggests that efforts to determine the economic impact of louse infestations are confounded by the lack of a uniform method to assess louse population levels.     

The significance of Nematodirus in New Zealand

Extract

Although Nematodirus species are commonlyfound in sheep in New Zealand, the worm had been considered to be of little economic importance until the period 1956–9 when a number of outbreaks of acute disease occurred in lambs; the condition was ascribed to heavy Nematodirus infestation. A similar situation had existed in the British Isles until about 1951 when outbreaks of acute nematodiriasis reached serious proportions.     

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.     

Prophylactic treatment with flumethrin,a pyrethroid (Bayticol?, Bayer), against Anaplasma phagocytophilum infection in lambs

Backgroud

Anaplasma phagocytophilum (formerly Ehrlichia phagocytophila) causes the disease tick-borne fever (TBF) in domestic ruminants and has for decades been one of the main scourges for the sheep industry in the coastal areas of Norway. Current control strategies are based on reduction of tick infestation by chemical acaricides.

Methods

In the present study, we investigated if frequent pour-on applications of pyrethroids would reduce tick infestion rate and seroprevalence of A. phagocytophilum infection in sheep. Forty lambs, one month old, of the Norwegian White Sheep breed were used. The lambs belonged to the experimental sheep flock at the Department of Production Animal Clinical Sciences. None of the lambs had been on I. ricinus infested pasture before turnout (day 0). All lambs were twins and twenty lambs were treated with a pour-on pyrethroid (Bayticol®, Bayer A/S, DK-2300) with a dose of 5 ml on days 0, 14, 28, 42, 56, 70, 84, 98, 112 and 128. Twenty lambs were untreated controls. The lambs were collected every fourteen days on pasture for treatment. In addition, the lambs were examined for ticks, blood sampled, weighed, and rectal temperature was recorded.

Results and conclusion

A significant reduction in tick infestion rate was detected on treated lambs. However, the present results indicate that frequent acaricide treatment does not reduce the seroprevalence to A. phagocytophilum on tick-infested pasture.     

Linognathus vituli (Anoplura: Linognathidae): population growth,dispersal and development of humoral immune responses in nai;ve calves following induced infestations

Growth of Linognathus vituli populations following establishment at a point source was followed for 16 weeks on eight louse-na?ve Holstein calves. Dispersal of lice from the point of infestation (withers) was monitored by examination of known louse predilection sights. Mean louse indices increased during the initial weeks reaching maximum mean values at 8 weeks post-infestation (p.i.). Subsequently, mean indices decreased, reaching a plateau that persisted through weeks 14 and 15 p.i. There was little movement away from the withers until 5 weeks p.i. Subsequently, numbers of lice on the withers declined, while increasing at sites on the head. A few lice were noted on the dewlap and topline sites. Host antibody responses to crude nymph antigens, measured by enzyme-linked immunosorbent assay (ELISA), were generally evident within 2-4 weeks of infestation. Examination of individual host data showed louse populations could be categorized relative to the mean population size for the group. Two animals were considered 'chronic', having louse populations that persisted throughout the study and whose louse indices were >150% of the group mean. Two animals were classified as 'resistant' having lice present for only a portion of the study and whose louse indices <40% of the group mean. The remaining animals had louse indices between 62 and 137% of the group mean. Antibody profiles of the individuals were not as clearly categorized, although the 'resistant' animals were only positive for short periods of time, roughly corresponding to the time when lice were observed.     

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.     

Effect of Haemaphysalis punctata infestation on growing lambs and rabbits

Lambs infected with adult Haemaphysalis punctata and rabbits infected with nymphs developed a macrocytic normochromic anaemia during seven and six successive infestations, respectively. The anaemia was directly proportional to the degree of infestation but disappeared several days after the termination of infestation. A leucocytosis, due to neutrophilia, was seen in both lambs and rabbits. Rabbits developed a thrombocytosis and reticulocytosis. Infested lambs grew less rapidly than uninfested animals. Signs of tick toxicosis and several other clinical manifestations appeared in both infested sheep and rabbits. Circulating antibodies against salivary antigen of adult H punctata were demonstrated in the sera of infested lambs by the micro-ELISA test. Titres were first detected on day 3 after infestation and increased gradually as infestation progressed. No precipitating antibodies in either infested sheep or rabbits were detected.     

Immunization of sheep against the larval stage of Taenia multiceps

A trial with 200 ewes and 127 lambs showed that vaccination of lambs with 2 doses of Oncosphere Secretory Antigen (OSA) 4 weeks apart, at either 4-8 and 8-12 weeks or at 12-16 and 16-20 weeks of age, was equally effective in protecting them against infestation with the larval stage of Taenia multiceps. In this trial, the lambs of ewes, vaccinated with OSA when they were 90 and again 120 days pregnant, were as susceptible to infestation as the lambs of untreated control ewes. Another trial to provoke passive immunity in lambs gave inconclusive results. In a 3rd trial 2 doses of regular OSA and 2 doses of freeze-dried OSA protected all the lambs in each group, while a single dose of regular OSA protected 9 out of 10 lambs against cerebral lesions.