The efficacy of showers for control of ectoparasites of sheep.

Ectoparasites of sheep in Britain include the tick Ixodes ricinus, the blowfly, Lucilia sericata, the ked, Melophagus ovinus and the lice, Damalinia ovis and Linognathus ovillus. The most important ectoparasite, however, is the mite Psoroptes communis ovis which causes sheep scab. This notifiable disease was eradicated from Britain in 1952 but was reported again in 1973. The control of ectoparasites depends largely on the efficient application of insecticide to the fleece and skin. Plunge dipping in a bath is generally regarded as the most efficient method and is compulsory for the control of sheep scab but it is not always the most convenient. After the eradication of sheep scab in 1952 plunge dipping was no longer compulsory and jetting, spraying and showering techniques were then employed for the other ectoparasites.     

The rate of spread of sheep scab within small groups of Merino and Dorper sheep

A single Merino sheep, artificially infested with the sheep scab mite, Psoroptes ovis, and a similarly infested Dorper sheep were placed with 9 uninfested Merino or 9 uninfested Dorper sheep respectively during winter and the rate of spread of infestation on the uninfested sheep observed. The same procedure was repeated in summer. It took 14 and 8 weeks respectively in winter before all sheep in the 2 groups displayed lesions of sheep scab, whereas in summer it took 10 and 12 weeks before all sheep had lesions.     

Sheep scab--environmental considerations of treatment with doramectin.

The paper reviews the recent change in attitudes to dipping sheep and the proposed legal requirements to prevent and treat sheep scab. The implications of fulfillment of all the requirements of the European Groundwater Directive and the probable resultant increase of the use of injectable endectocides as an alternative to plunge dipping are discussed in relation to their likely frequency of use and potential ecological impact. In particular the properties of doramectin, one of the most recently introduced, are examined in relation to its use for the treatment of sheep scab.     

Outbreak of sheep scab on two adjacent common alpine pastures in the canton of Schwyz (Switzerland)

Sheep scab, which is caused by the mite Psoroptes ovis, is a notifiable disease in Switzerland. In the framework of an epidemiological study in the canton of Schwyz, a sheep scab outbreak on 2 adjacent alpine pastures with 62 flocks (1770 sheep) was followed up clinically, parasitologically and serologically. No mass treatment of the flocks with organophosphates or avermectins had been undertaken before the flocks were taken up to the alpine pastures, but they were treated according to their serological status. Supervised treatment of seropositive judged flocks (at least one seropositive or at least 2 serologically equivocal animals per flock) with Doramectin was undertaken, whilst seronegative judged flocks remained untreated. Sheep returned from the summer pastures in early September 2001 and within three months scab infestation was diagnosed in 53 flocks (85.5%). These infested flocks were scattered all over the canton. Furthermore, the transfer of sheep from 6 infested flocks resulted in the transmission of the disease to 10 new flocks. Infested flocks were kept in quarantine and sanitized. The complexity of the traditional use of shared alpine pastures and the intense, uncontrolled trading with animals render the control of sheep scab difficult.     

Prevalence, regional distribution and control of blowfly strike in England and Wales.

The prevalence and control of blowfly strike in England and Wales was investigated by a postal survey of 2451 sheep farmers, divided into five regions, who were asked about the blowfly seasons of 1988 and 1989. These were important years for the control of blowfly strike because the number of compulsory dips for the control of sheep scab was reduced from two to one in 1989. The response rate was 74.2 per cent. A larger proportion of farmers in the south west and south east reported strike (90 per cent), than in the north of England (60 per cent). The proportion of sheep with strike showed a similar regional variation (0.7 per cent in the north of England to 2.8 per cent in the south west). Dipping was the most common method of blowfly control, followed by tail amputation, dagging, spraying and cyromazine. Twenty per cent of farmers reported reducing the frequency of dipping in 1989, and of those 20 per cent increased the frequency of spraying and 20 per cent used cyromazine.     

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.     

Use of a colouring agent in approved dips as an aid in identifying dipped sheep

A fat soluble dye was identified as a suitable colourant for mixing with approved dips during the statutory winter dipping period. The optimum concentration of the dye was 0.4 per cent. It uniformly dyed the sheep and depending on the breed persisted on the fleece for three to six months. Any dye that remained on the wool at shearing (six to eight months after dipping) was washed out by scouring solutions containing non-ionic and anionic detergents. The dye did not alter the efficacy of the commonly used insecticides.     

The in vitro response of sheep scab mites to pyrethroid insecticides.

The response of sheep scab mites to pyrethroid insecticides and organophosphate compounds was studied in vitro with the objective of finding a simple test for detecting insecticide resistance in scab mites. Psoroptes cuniculi from rabbits or P. ovis from sheep were enclosed in small 'tea bags' made from heat sealable paper prior to dipping in insecticide. Mites failed to die 24 h after a 1 min dip in working concentrations of insecticidal sheep dips. With flumethrin a variety of different conditions were tested but most failed to improve the efficacy of flumethrin. It is suggested with freshly collected mites pyrethroids may be taken up by ingestion.     

Sheep scab outbreaks in Great Britain between 1973 and 1992: spatial and temporal patterns.

In January 1973, the mange mite Psoroptes ovis was found in a sheep flock in Lancashire, UK after a 20 year period of eradication. Over the next 20 years, a total of 1480 flock outbreaks were reported, until June 1992 when the control of sheep scab was deregulated. The spatial and temporal patterns of the number of outbreaks in each month over this period were analysed using time series methods, a geographical information system (GIS) and second order approaches to the exploration of space-time interaction (K-function analysis). The monthly time series displays clear evidence of seasonal cyclicity, with most outbreaks being reported in the winter months. After removal of the summer compulsory dip in 1988 however, there is evidence of a change in the seasonal pattern, with more cases being reported in the autumn months. There is also evidence of a contribution from a sinusoidal wave with a period of 8 years, which roughly corresponds to the major changes in the national control policy. The spatial pattern also appears to expand and contract on a roughly 4 year cycle, again reflecting the oscillating periods of success and failure. Examination of the spatial and temporal pattern revealed strong evidence of space-time clustering (p < 0.001) and a major contribution to the pattern from very local (< 12 km) spread within 5 months of an arbitrary outbreak.     

Treatment of psoroptic mange with reference to epidemiology and history.

Treatment methods in the last century involved the use of substances such as sulphur, mercury, hellebore, arsenic, nicotine and others, applied in various ways. The advent of dips in 1843 signalled an advance. However, the biology of the mite, Psoroptes ovis, the epidemiology of sheep scab and the lack of persistence of the acaricides necessitated repeated laborious treatments to ensure success. In 1947 this changed with the use of organo chlorines (OCs) which had up to 3 months residual activity. The use of OCs led to the eradication of psoroptic mange of sheep in USA. Organo phosphates (OPs) were introduced in the late fifties and synthetic pyrethroids (SPs) in the early seventies. In 1985, due to sheep tissue residues, lindane (OC) was withdrawn from the market and this greatly reduced the capacity for effective sheep scab control. Before the arrival of the endectocidal avermectin, ivermectin in 1978 and its successful use as an acaricide in 1992, control of psoroptic mange was limited to plunge dipping. In 1994 moxidectin, a milbemycin, was found to be effective and to have the added benefit of at least 4 weeks persistent activity. Another avermectin doramectin was shown, in 1995, to successfully treat scab and recently an ivermectin bolus has been introduced which has a 100 days' activity and is fully therapeutic and prophylactic. Strict attention to detail in the use of injectable products is essential in order to achieve satisfactory results. Work is progressing on the use insect growth regulators (IGRs) and also on naturally occurring substances such as linalool, neem and lavender oil. At the CVRL Dublin, promising results have been achieved with neem and some IGRs. Other areas of interest are allemones, synergists, microclimate manipulation, sheep breed resistance and vaccines. Successful control depends on epidemiological knowledge, accurate diagnostic techniques, intimate knowledge of the mite's life cycle, its behaviour on and off the host, its macro and molecular biology, the nature of the pathogenesis of the disease, sheep husbandry practices, nutritional and environmental factors; also farmer awareness and attitudes. The variable responses of sheep to the mite, the unpredictable incubation period, course, manifestations and outcome make this an intriguing and perplexing disease. Ways to overcome these problems and to achieve possible eradication are discussed.     

国产赛福丁对绵羊的毒性及治疗绵羊痒螨病的效果

应用国产赛福丁对3组绵羊(每组3只)分别以10、20、40 mg/kg剂量进行了毒性试验。结果,10、20 mg/kg剂量的绵羊,药后临床未出现任何毒性反应;40 mg/kg剂量的绵羊,均于药后40～60 min出现了典型的有机磷中毒症状。全血胆碱酯酶对赛福丁非常敏感,但其抑制程度与中毒靠状的出现并无直接关系。中毒后血清GOT和GPT无变化。以50、100、200、250 ppm浓度的赛福丁溶液分别药浴患痒螨绵羊,均可迅速地治愈患羊,浴后24 h即可杀灭全部螨虫,24～72 h痒觉消失,2周后脱痂,长毛。近期疗效同于倍特和林丹.而远期疗效优于倍特和林丹。证明国产赛福丁是一种高效、低毒的杀螨剂。     

Survey of levels of propetamphos and diazinon used to control sheep scab in Northern Ireland

As a result of an increase in the incidence of sheep scab in Northern Ireland, the concentrations of propetamphos and diazinon were measured during 1987 and 1988 in fleece and liquid dip samples from selected flocks, including some in which inadequate dipping was suspected. Sixty-five per cent and 68 per cent of the liquid dip samples contained less than the manufacturer's recommended maintenance concentrations for propetamphos and diazinon respectively. The concentrations found in fleece were also lower than those found in sheep which were dipped with the recommended concentrations of propetamphos and diazinon in a controlled experiment.     

Effect of the interval between shearing and dipping on the spread of Corynebacterium pseudotuberculosis infection in sheep

OBJECTIVE: To determine whether the spread of Corynebacterium pseudotuberculosis infection to sheep in dips could be controlled by increasing the time between shearing and dipping. DESIGN: A controlled treatment trial where only the time between shearing and dipping was varied. ANIMALS AND PROCEDURE: One hundred and ninety-five sheep were found to be negative for C. pseudotuberculosis exposure by assay of CLA toxin antibody, were divided into four treatment groups. Each was shorn at either 0, 2, 4 or 8 weeks before dipping in a solution containing C. pseudotuberculosis. Blood samples were taken 6 weeks after dipping and sheep were slaughtered 12 weeks after dipping. A fifth smaller group of 14 sheep shorn 26 weeks before dipping, was also exposed to C. pseudotuberculosis and was slaughtered with the other sheep. RESULTS: The occurrence of caseous lymphadenitis abscesses did not differ between groups or with sheep shorn 26 weeks before dipping. The proportion of sheep that seroconverted to the C. pseudotuberculosis toxin and cell wall ELISA was larger in sheep dipped immediately after shearing than in sheep in the other groups. CONCLUSIONS: Delaying dipping until 8 weeks after shearing did not decrease the C. pseudotuberculosis infection rate due to dipping. Sheep dipped immediately after shearing developed higher concentrations of antibody to C. pseudotuberculosis than sheep when dipping occurred between 2 and 8 weeks and later after shearing.     

The epidemiology and diagnosis of bluetongue with particular reference to Corsica

Bluetongue (BT) and/or BT viruses (BTV) have been identified in the Mediterranean basin and the Balkans each year from 1998 to 2002 and in particular BTV serotype 2 in the French Island of Corsica (2000 and 2001). In response to these virus incursions, the French Veterinary Authorities carried out epidemiological studies that included virological, serological and entomological analysis, and two vaccination campaigns performed in the winter of 2000/2001 and the winter and spring of 2001 and 2002. Rapid and reliable serotype differentiation is essential at the start of an outbreak to allow an early selection of vaccine to control the spread of the virus. Thus, molecular tools, that complement conventional methods, have been developed for early detection of infection, determination of the serotype, and differentiation between natural infection and vaccination. Serological results showed that the first vaccination campaign during the winter of 2000/2001 did not provide full protection for all sheep and during the summer of 2001, 335 sheep flocks in Corsica were again infected by BTV 2 (7-fold more that in 2000). Entomological studies have demonstrated that the only proven vector of the disease, Culicoides imicola, was present in the island in 2000 and that it has successfully established itself in Corsica. The safety and immunogenicity of the commercial South African vaccine were studied. Fourteen sheep were vaccinated and then observed for clinical signs. Blood, sera, spleen and lymph nodes were collected and analyzed, and the results confirmed the safety and potency of using this vaccine to protect sheep from clinical disease. As a result, an intensive vaccination campaign was performed during winter and spring 2001/2002. No cases of BT had been observed by the end of summer 2002, indicating that the vaccination campaign has been successful in protecting sheep from infection.     

青海三角城种羊场草场硒的季节变化及其盈缺分析

经过对青海省三角城种羊场夏(6月中旬)、秋(9月中旬)、冬(12月中旬)三季的水、土壤、牧草、绵羊被毛、血液、组织器官及粪中硒的含量进行调查分析,结果表明,三角城种羊场夏季土壤和牧草严重缺硒;绵羊血浆硒浓度全年均属正常;肝硒浓度低于临界水平;粪硒浓度冬季低于0.1mg/kgDM的正常值;被毛硒则在夏秋两季稍高,冬季严重缺乏,仅为0.012 mg/kg,极显著的低于羊毛缺硒值0.079 mg/kg(P<0.01).     

藏系绵羊瘤胃细菌数量及其放牧地牧草养分随季节变化的研究

试验分别于春、夏、秋和冬季,随机选择3只同群常年放牧健康的藏系绵羯羊(2岁),屠宰后采集瘤胃内容物。采用瘤胃细菌通用引物和实时定量PCR技术,研究瘤胃细菌数量随季节的动态变化。结果表明,1)夏季瘤胃细菌数量显著(P＜0.05)高于其他3个季节,分别是春季、秋季、冬季细菌数量的5.56,2.35和2.49倍;秋、冬季是春季细菌数量的2.38和2.23倍;而秋和冬季瘤胃细菌的数量差异不显著(P＞0.05)。2)夏季藏系绵羊采食量分别为春季、冬季和秋季的1.98,1.61和1.80倍,饲料中的纤维性物质含量增高,采食量也随着降低,瘤胃细菌的数量也相应降低;3)实时定量PCR技术能准确的反映出放牧藏系绵羊瘤胃细菌数量随季节的动态变化。     

Breeding programmes for TSE resistance in British sheep. II. Assessing the impact on the prevalence and incidence of scrapie

By establishing a breeding programme for transmissible spongiform encephalopathie (TSE) resistance, there are plans to eradicate sheep TSEs from member states of the European Union (EU). In this paper, we used a simple age- and genotype-structured model to assess the impact of four breeding strategies on the prevalence and incidence of scrapie in the British sheep flock. The strategies ranged from the minimum EU requirements to compulsory implementation of the current National Scrapie Plan for Great Britain (NSP). All four strategies were predicted to reduce the prevalence and incidence of disease, though there was likely to be a delay of several years between the implementation of a breeding programme and the reduction in incidence. There were differences in the efficacy of the strategies, with the most stringent resulting in the greatest reduction in prevalence and incidence. However, the magnitude of the differences was not great, largely because all four strategies eliminated the VRQ allele, which is associated with a markedly higher risk of disease than any of the other alleles. Sensitivity analyses indicated that the model results were robust to selection bias when estimating the risk of infection; and that the efficacy of a breeding programme was unlikely to be compromised, unless the risk of infection is substantially underestimated by data on clinical disease.     

Integrated control strategies for ectoparasites in Scottish sheep flocks

Ectoparasite infestations of sheep can result in serious animal welfare and financial losses. Many of the veterinary medicines used in their control can be harmful to humans and other species. These undesirable side-effects mean that trade-offs may be necessary and make it difficult to determine ‘the best’ control strategy. This problem is common to many animal health/welfare concerns, and must be addressed if progress is to be made under the Animal Health and Welfare Strategy for Great Britain. This paper describes an approach to such cases using a disease model to identify the financially optimal ectoparasite control strategies at the farm level for Scottish conditions in a climate of changing control restrictions. Our approach takes a wider systems perspective than is usual in cost-benefit studies of animal disease. The findings demonstrate that both flock size and ectoparasite risk are determinants of optimal control strategies. In addition the benefits of livestock biosecurity practices (isolation and treatment of incoming stock) for the control of sheep scab are demonstrated. The importance of dip products for the effective control of ectoparasites is discussed and possible implications if these become unavailable or the cost of their usage increases. Interdependence between stakeholders is highlighted, indicating a need for regional co-operation between farmers and a more integrated approach to control of some farm animal diseases.     

Endemic sheep scab: risk factors and the behaviour of upland sheep flocks

Since the deregulation of sheep scab in 1992, the number of scab outbreaks per year in the UK has increased rapidly; there has been an estimated 60-fold increase in outbreak incidence between 1992 and 2007. How best to focus management or eradication efforts has therefore been an issue of ongoing debate. Previous work has shown that scab outbreaks occur repeatedly on some farms whereas others never or rarely experience outbreaks. Here, to consider why this pattern occurs, and to quantify the risk of scab associated with different husbandry practices, face-to-face interviews with farmers at 16, randomly selected, repeat-outbreak farms and 16 matched farms with no or little history of scab over the previous 10 years, were used to identify associated risk factors. This showed that farms using common grazing were at significantly higher risk of infestation than farms not using common grazing, as were farms that had direct contact with neighbours' sheep and that had neighbours with scab. To further demonstrate the risk of common grazing, a survey of sheep on one common in south Wales showed that there was significant mixing of sheep from three farms, highlighting the potential for scab transmission between flocks. Common grazing, associated with upland regions, would appear to be the largest single obstacle to effective national scab control in the UK. The results suggest that a cost-effective approach to scab control may be to consider upland and lowland farms as separate epidemiological systems, with upland regions requiring a co-ordinated, systematic approach to achieve any significant management of the problem. In contrast, on lowland farms outbreaks are already largely contained effectively through good biosecurity and treated on a case-by-case basis if they occur.     

Control and management of sheep mange and pediculosis in Great Britain

The patterns of insecticide use for the prevention and control of sheep lice and Psoroptes mites, in England, Wales and Scotland, in 2003-2004, were examined using data from a retrospective questionnaire. Overall, 375 of the 966 (39%) farmers who responded said that they treated at least once to prevent louse infestation. For scab, 426 of the 966 (44%) farmers who responded said that they had treated prophylactically to prevent the disease. There were no significant differences between regions in the number of times farmers treated to prevent lice (chi(2)=0.54, P>0.1) or scab (chi(2)=0.16, P>0.1). Among the farmers who applied prophylactic treatment 23% had a subsequent outbreak of lice and 17% had an outbreak of scab. The majority of sheep farmers who used preventative treatment did so in June and July. Where a second treatment was given it was largely in October. For lice, 52% of farmers used pyrethroids to prevent and 70% to treat louse infestation. For scab prophylaxis, most farmers said that they used either the macrocyclic lactones (41%) or organophosphates (36%) as a preventative. For the therapeutic treatment of scab outbreaks, macrocyclic lactones (largely doramectin) were used on 58% of sheep farms. The high national prevalence of sheep scab and pediculosis indicates that current control methods are failing to contain these ectoparasites. The results of this study suggest that a large proportion of insecticide applications take place at times of year when they might expect to be relatively ineffective, and the use of inappropriate compounds for the parasites in question is common. The widespread use of macrocyclic lactones in particular for scab prevention and control is of concern, because of the additional use of these compounds in parasitic worm control and the potential that their overuse will hasten the development of resistance.