Border disease without nervous signs or fleece changes

A natural infection with border disease virus occurred in a flock on low ground in Argyll in the spring of 1984. The outbreak was unusual in that the typical clinical signs of border disease, ie, tremor and, or, fleece changes were not present; manifestations of disease were restricted to abortion and the birth of small weak lambs. The disease was shown to have been introduced to the flock by four healthy ewes persistently infected with border disease virus among a group of 39 purchased in October 1983. Further investigations in late August 1984 detected viraemia in six of seven ill-thriven lambs and four of 24 apparently healthy lambs. Attempted 'natural vaccination' of susceptible sheep by mixing them at grass for three months with groups of ewes and lambs known to contain virus excretors was largely unsuccessful as only four of 22 'sentinel' sheep seroconverted. In October 1984 the persistently infected purchased animals and all that year's lamb crop were removed from the farm. No disease occurred in 1985 when the lambing percentage was 129 per cent compared with 100 per cent in 1984. Two of the four persistently infected purchased ewes were mated at Moredun Research Institute in December 1984 and both produced healthy but persistently infected lambs.     

The production and survival of lambs persistently infected with border disease virus.

From 1985 to 1989 lambs persistently infected with border disease virus (BDV) were produced for comparative immunological studies by infecting 57 susceptible pregnant ewes between 50 and 60 days' gestation with Moredun or Oban strains of BDV. Ewes were infected either by injection with virus grown in cell culture or by housing with lambs excreting BDV. There was no significant difference in the outcomes of these different methods of infection. There was a significant difference in the number of viable lambs born to ewes receiving the two viruses. Of 41 ewes infected with Moredun virus 21 produced 32 live lambs of which 17 were reared to 1 month old (53% viability). Of 16 ewes receiving Oban virus 10 gave birth to 17 live lambs of which 15 were reared to 1 month old (88% viability). All the lambs born to ewes infected with Moredun BDV had varying signs of tremor and increased hairiness ("hairy-shakers") while those born to ewes infected with the Oban virus had no obvious clinical signs. Survival of the lambs was poor. Up until February 1991, 14 Moredun and 10 Oban sheep between the ages of 4 months and 5.5 yr had died from a variety of causes. The two commonest causes were a chronic wasting syndrome and a mucosal disease-like syndrome which was associated with the recovery of cytopathic BDV. Mating of unrelated persistently infected sheep was largely unproductive although 2 lambs were reared.     

口蹄疫病毒受体整联蛋白在绵羊不同发育阶段组织中mRNA转录水平的分析

口蹄疫病毒野毒株利用整联蛋白（integrin）αvβ1、αvβ3、αvβ6和αvβ8作为受体侵入细胞。本研究采用实时逆转录聚合酶链反应（qRT-PCR）技术,定量检测绵羊胎儿（45、75和110 d的绵羊胎儿）、新生羔羊和成年绵羊组织中整联蛋白亚单位αv、β3、β6和β8转录水平。比较分析发现,在蹄冠上皮组织中,成年绵羊和新生羔羊的β6 mRNA水平低于75和110 d胎儿的;在心组织中,成年绵羊、新生羔羊和110 d胎儿的β6 mRNA高于45和75 d胎儿的;在肌肉组织中,胎儿和新生羔羊的β6以及β8 mRNA水平高于成年绵羊的;在舌上皮组织中,成年绵羊的β3 mRNA水平低于其他发育时期的。在软腭组织、扁桃体中整联蛋白mRNA水平在胎儿、新生儿和成年绵羊之间变化不大。本研究首次获得相关整联蛋白mRNA在绵羊不同发育阶段组织中分布的定量数据,为了解整联蛋白在口蹄疫病毒感染组织嗜性中的作用机制提供新的科学依据。     

Establishment of a maedi-visna-free flock after the purchase of infected sheep

Maedi-visna (MV) infection was detected in a cohort of 68 purchased ewes, one of several groups of sheep introduced to a farm after the previous stock had been culled with suspected foot-and-mouth disease in 2001. Except for short periods totalling six to seven weeks when the sheep co-grazed with 13 ewe lambs and ram lambs, the infected cohort was kept separate from other sheep on the farm over a total of 21 months. During this period two crops of lambs were reared from the infected ewes. All the lambs were fattened and killed, and all ewes were culled after the second crop of lambs had been weaned. Subsequent serological testing of the remaining sheep on the farm confirmed the elimination of MV infection from the flock, leading to its acceptance in the Maedi Visna Accreditation Scheme of the Scottish Agricultural College's Sheep and Goat Health Schemes.     

A MUCOSAL DISEASE VIRUS AS A CAUSE OF ABORTION, HAIRY BIRTH COAT AND UNTHRIFTINESS IN SHEEP

A condition in Australian sheep resembling border disease was transmitted by the inoculation of pregnant ewes with material from affected lambs. This material contained mucosal disease virus (MDV). Twenty-two lambs comprising 6 from uninoculated control ewes, together with 11 with hairy coats and 5 with normal coats from inoculated ewes, were observed from 7 to 182 days after birth. Nine of the lambs from inoculated ewes died during the experiment from a variety of causes. Glial cell abnormalities were observed in control and affected lambs, but only 4 of the 11 hairy lambs were judged to have abnormal glial cells. There were no consistent histopathological findings indicative of MDV infection. MDV was recovered from tissues of all 11 hairy lambs, but not from any of the lambs with normal coats. The hairy lambs appeared to be immunologically tolerant to the virus. Susceptible sheep in contact with the hairy lambs were infected with MDV. It is suggested that a condition in Australian lambs characterised by hairiness of the birth coat and poor viability is due to foetal infection with a mucosal disease virus.     

TRANSMISSION OF A MUCOSAL DISEASE VIRUS INFECTION BETWEEN SHEEP

The transmission of mucosal disease virus (MDV) from infected ewes and their lambs to susceptible sheep was investigated. MDV was recovered from the amniotic fluid of an infected pregnant ewe and from the blood, nasal swabs and urine of hairy lambs. MDV infection was transmitted either at lambing, from infective foetal fluids or lambs, or later as a result of contact with a surviving with a hairy lamb and either aborted or gave birth to an infected hairy lamb. Adult sheep and 12-months-old sheep were less readily infected than were newborn lambs. Pregnant ewes were infected by contact with a hairy lamb and either aborted or gave birth to an infected hairy lamb. A method to minimise spread of the infection in the field is suggested.     

Border disease in sheep caused by transmission of virus from cattle persistently infected with bovine virus diarrhoea virus.

Two outbreaks of border disease occurred on farms with sheep flocks and breeding cattle. The infection of the pregnant sheep was probably caused by transmission of virus from calves persistently infected with non-cytopathic bovine virus diarrhoea virus (BVDV) which were kept in close confinement with the ewes during mid-pregnancy. Border disease was also induced experimentally in eight lambs by exposing their dams at 38 to 78 days of gestation to a heifer persistently infected with BVDV. Both the natural and the experimental infections were characterised by typical signs such as 'hairy-shaker' lambs and high lamb mortality. The diagnosis was confirmed by virus isolations from live-born lambs, seroconversion and pathology. The study supports the assertion that cattle persistently infected with BVDV and in close contact with pregnant sheep, are an important source of strains of virus capable of causing border disease.     

Pilot project for eradicating maedi-visna in Walliser blacknose sheep

Maedi-Visna is a lentiviral disease of sheep with a worldwide distribution. The transmission of the virus occurs primarily via colostrum and milk from the infected ewe to its newborn lamb but also horizontally between sheep. The most obvious clinical symptoms are progressive dyspnea and emaciation. In this prospective study an eradication based on serological testing and removing of seropositive animals was performed in 24 flocks of sheep of the breed "Walliser Schwarznasenschafe" leading to a reduction of the seroprevalence from 36% to 1% within two years. The control group consisted of 21 flocks of sheep. Lambs of seropositive ewes had a 7.6 times higher risk to seroconvert within their first two years of life compared to those of seronegative ewes. The dynamics of the spread of the infection were studied in birth cohort groups. Cohort animals of seropositive ewes showed an obvious trend to seroconvert slowly. Seropositive ewes had a significantly lower reproduction rate and their lambs suffered from significantly higher death and lower growth rates, probably due to a reduced milk production, resulting in economic losses.     

Border Disease Virus Transmitted to Sheep and Cattle by a Persistently Infected Ewe: Epidemiology and Control

In a Swedish sheep flock comprising 202 ewes and 13 rams, a pair of twin lambs born in the spring of 1990 demonstrated signs of border disease (BD) and were persistently infected (PI) with border disease virus (BDV). Investigation showed that BDV had been introduced in the preceding tupping period 5-6 months earlier by a bought-in ewe which, on the basis of immunoperoxidase- and polymerase chain reaction techniques, was shown to be PI with BDV. Only 7 of the ewes, all of which had been in close contact with the PI ewe, seroconverted during the subsequent gestation. Apart from the PI twin lambs the losses caused by BDV were restricted to 2 barren ewes. The twin lambs, the PI ewe and lambs from the other 4 ewes that seroconverted were removed from the flock. The flock was thereafter free from an ongoing infection with BDV as shown by the absence of seroconversion.In addition, 5 heifers in late pregnancy most probably seroconverted to bovine virus diarrhoea virus (B VDV) when kept in close contact with the same PI ewe during the winter of 1989-90. When these heifers were reintroduced to the BVDV-free dairy herd from which they originated, their serum antibody titres ranged between 1:250 and 1:1250. Neither these heifers - nor their calves–caused any spread of the infection in the herd, as indicated by the absence of seroconversion in 70 cows. The present investigation shows that in the control of both BDV in sheep and BVDV in cattle, it is important to ensure that the risk of transmission of pestivirus between the 2 species is minimized.     

A MUCOSAL DISEASE VIRUS AS A CAUSE OF ABORTION HAIRY BIRTH COAT AND UNTHRIFTINESS IN SHEEP

A condition resembling border disease has been transmitted by the inoculation of pregnant ewes with material from affected lambs. Forty-nine merino ewes, mated to merino rams 7 to 87 days previously, were inoculated with an homogenate of brain, spinal cord and spleen from affected lambs. Mummified foetuses, abortions and stillbirths were observed, and lambs with hairy birth coats were born to ewes inoculated between days 12 to 70 of gestation. A mucosal disease virus (MDV), present in the original material, was recovered from the aborted foetuses and lambs. Attempts to induce passive protection using bovine anti-serum to the C24V strain of MDV were not successful. The condition was also transmitted by inoculation of pregnant ewes with a cell culture supernatant prepared from tissue cultures that had been inoculated with an organ homogenate pool. MDV was present in the supernatant and was recovered from aborted foetuses and lambs. It is suggested that a condition in sheep in Australia resembling border disease is due to the infection of the pregnant ewe by a mucosal disease virus.     

Morphometric analysis of growth retardation in fetal lambs following experimental infection of pregnant ewes with Border Disease virus

The onset of growth retardation was investigated in fetal lambs following experimental infection of pregnant ewes with Border Disease virus ( ) on day 53 of pregnancy. Fetuses from control and infected ewes were harvested at weekly intervals between day 60 and day 95 of gestation and morphometric studies were completed on tibial radiographs and tibial growth cartilage metaphyseal junctions. Mean tibial areas were significantly reduced (P<0·01) in fetuses from infected ewes at 35 and 42 days after infection and growth cartilage metaphyseal junctions were less mature in fetuses from infected ewes at 42 days after infection. Positive immunostaining for BDV antigen was demonstrated in the brains of all fetuses from infected ewes between 14 and 42 days after infection. Attempts to demonstrate BDV antigen in bone proved unsuccessful. It is concluded that intrauterine growth retardation is an early manifestation of BDV infection in lambs and that the process is initiated shortly following infection of the fetus.     

Intrauterine transmission of ovine progressive pneumonia virus

Ovine fetuses, newborn lambs, and ovine colostrum were examined for ovine progressive pneumonia virus. The lambs and colostrum were also examined for specific antibody. Virus was isolated from 1 fetus, from 2 newborn lambs, and from most samples of colostrum. The fetus was about 100 days old and was carried by a seronegative ewe in contact with seropositive sheep. Both newborn lambs were carried by seropositive ewes. One lamb was dead at birth; the other lamb was normal and had not nursed. Antibody specific for the virus was present in the colostrum of 12 of 14 seropositive ewes and in the serum of 8 of 11 lambs that had nursed seropositive ewes, but not in the serum of lambs that had not nursed.     

不同品种受体对绵羊胚胎移植效果及羔羊早期生长性能的影响

旨在探讨以小尾寒羊和蒙古羊作为受体时,二者的胚胎移植效果及所产羔羊的早期生长性能之间的差异。选用南非肉用美利奴羊(n=11)和澳洲白绵羊(n=110)作为供体,以小尾寒羊(n=196)和蒙古羊(n=504)作为受体;对供体母羊进行超数排卵以及人工授精处理,记录供体母羊的收集胚胎总数和可用胚胎数,计算平均每只羊收集的可用胚胎数以及胚胎合格率;对小尾寒羊和蒙古羊进行同期发情及胚胎移植处理,记录受体母羊的产羔数,计算繁殖率;计算并比较不同受体母羊所产羔羊的平均初生重、成活率以及70日龄断奶羔羊数、70日龄断奶重、平均日增重、平均每只母羊提供的断奶羔羊数。结果表明,从供体母羊中共获得可用胚胎549枚,平均每只羊收集可用胚胎4.54枚,胚胎合格率为82.56%;利用胚胎移植技术,移植受体母羊529只,所产羔羊240只,平均繁殖率为45.37%;小尾寒羊的发情率和繁殖率明显高于蒙古羊;共获得70日龄断奶羔羊211只,羔羊成活率为87.92%,平均日增重为280.00g;小尾寒羊和蒙古羊所产的羔羊初生重没有显著差异(P>0.05),小尾寒羊所产羔羊的70日龄断奶重和平均日增重分别极显著(P<0.01)和显著(P<0.05)高于蒙古羊,而蒙古羊所产羔羊的成活率显著高于小尾寒羊(P<0.05);平均每只小尾寒羊母羊可提供的断奶羔羊数(0.42只)略高于蒙古羊(0.39只),小尾寒羊作为胚胎移植受体略具有优势。综合分析表明,在内蒙古兴安盟地区小尾寒羊和蒙古羊均可以作为胚胎移植的受体来使用。     

Longitudinal studies of naturally acquired Brucella abortus infection in sheep.

Naturally acquired Brucella abortus infections were studied during consecutive pregnancies in eight sheep and in their lambs over a period of 40 months to evaluate epizootiologic aspects of natural infection in sheep. Brucella abortus was isolated from the ewes following 16 of 26 natural terminations of pregnancy: from 5 of 6 ewes in the first year, from six of eight ewes in the second year, from two of six ewes in the third year, and from three of six ewes in the fourth year. Vaginal swab samples and milk samples were the most consistent source of the brucella organisms. Brucella abortus was isolated from three ewes when standard tube test seroagglutination titers were less than 1:100. In contrast, results of supplemental tests (card, 2-mercaptoethanol, complement-fixation, and Rivanol) remained positive during the study. During the 40 months, B abortus was isolated from 4 of 4 aborted fetuses, 2 of 5 stillborn lambs, 10 of 37 living lambs, and as an indicator of continuing infection, from 6 of 12 lambs born during the fourth year. Although B abortus has a definite host preference for cattle, this study demonstrated that under appropriate management conditions, sheep may be naturally infected and may remain infected for more than 40 months. Epizootiologic evaluation of all factors, including husbandry practices and exposure potential, should be utilized in determining the need to test other species that may have been exposed to cattle infected with B abortus.     

Prevalence and effect of subclinical ovine progressive pneumonia virus infection on ewe wool and lamb production

The prevalence of infection with ovine progressive pneumonia (OPP) virus and its effects on ewe wool and lamb production were investigated in a flock of 2,976 ewes of 6 breed types (Rambouillet, Targhee, Columbia, Polypay, 1/4 cross Finnsheep, and 1/2 cross Finnsheep). Prevalence of seropositivity was significantly (P less than or equal to 0.01) lower among Rambouillet and Targhee breeds (44 and 42%, respectively), intermediate in Polypay, Columbia, and 1/4 cross Finnsheep (approximately 53%), and higher among 1/2 cross Finnsheep (62%). Seropositivity increased with age in all breed types from 11% at 1 year of age to 93% at greater than or equal to 7 years of age. Lateral disease transmission is indicated by linear increase of seropositivity prevalence with increasing age, including that in sheep greater than 6 years old. Subclinical infection with OPP virus had no apparent detrimental effect on number of lambs born, lamb viability, birth weight, number of lambs weaned, or growth rate of single and twin lambs, compared with findings for noninfected sheep in the same flock. Mature ewe body weight and grease fleece weight did not differ between subclinically infected seropositive and seronegative ewes. Subclinical infection with OPP virus does not appear to have an adverse economic effect on ewe wool and lamb production. Culling rate attributable to clinical manifestation of infection with OPP virus must be accurately determined before the true effects of virus infection on production can be determined and an eradication program can be recommended.     

Efficiency of Duddingtonia flagrans against Trichostrongyle infections of sheep on mountain pastures

The control of sheep nematode parasites in extensive mountain/transhumant management systems using the nematophagous fungus Duddingtonia flagrans was assessed in this study. Two groups of Churra Tensina ewes were allowed to graze for 8 weeks in autumn on two separate paddocks of infected pasture near their winter sheds in the valley. At lambing, ewes and their twin lambs were turned out into the same paddocks for the following 12 weeks. One group of ewes received a daily dose of 5 x 10(5) chlamydospores of Duddingtonia flagrans/kg live weight per day both in autumn and in spring, while the other group was used as a non-treated control. Daily dosing of grazing ewes with the fungus D. flagrans had a clear effect on reducing autumn pasture contamination. This had a subsequent effect on the over-wintering larvae population that was confirmed by a 20% lower worm burden of tracer lambs kept in early spring on the paddock previously grazed by fungus treated ewes. In spring, pasture contamination was also significantly reduced in the paddock grazed by fungi-treated ewes and their lambs showed a 61% lower worm burden and a better performance than the control lambs. Results herein show that fungal spores fed to sheep at critical times with regard to the epidemiology of parasite infection, can have a significant effect on the infective larvae present on pasture, which could further improve lambs performance. This novel approach to parasite control would be of interest amongst both organic and conventional sheep farmers operating in mountain regions.     

Nontransmission of bluetongue virus by embryos from bluetongue virus-infected sheep

Donor sheep were infected either by bites of bluetongue virus (BTV)-infected (serotype 11, "Texas Station strain") Culicoides variipennis or by inoculation with 100,000 median chicken embryo intravascular lethal doses of BTV (serotype 11) from a suspension made from infected C variipennis. Fourteen embryos from 4 BTV-infected ewes bred by rams not infected with BTV were transferred to 8 BTV-seronegative recipient ewes, and 35 embryos and 4 unfertilized eggs from 14 BTV-infected ewes bred by BTV-infected rams were transferred to 19 BTV-seronegative recipient ewes. Eleven pregnancies and 12 lambs resulted. None of the recipients or lambs seroconverted, and BTV was not isolated from the pregnant recipient ewes or their lambs at slaughter 30 days after parturition.     

Transplacental transmission of field and rescued strains of BTV-2 and BTV-8 in experimentally infected sheep

Transplacental transmission of bluetongue virus has been shown previously for the North European strain of serotype 8 (BTV-8) and for tissue culture or chicken egg-adapted vaccine strains but not for field strains of other serotypes. In this study, pregnant ewes (6 per group) were inoculated with either field or rescued strains of BTV-2 and BTV-8 in order to determine the ability of these viruses to cross the placental barrier. The field BTV-2 and BTV-8 strains was passaged once in Culicoides KC cells and once in mammalian cells. All virus inoculated sheep became infected and seroconverted against the different BTV strains used in this study. BTV RNA was detectable in the blood of all but two ewes for over 28 days but infectious virus could only be detected in the blood for a much shorter period. Interestingly, transplacental transmission of BTV-2 (both field and rescued strains) was demonstrated at high efficiency (6 out of 13 lambs born to BTV-2 infected ewes) while only 1 lamb of 12 born to BTV-8 infected ewes showed evidence of in utero infection. In addition, evidence for horizontal transmission of BTV-2 between ewes was observed. As expected, the parental BTV-2 and BTV-8 viruses and the viruses rescued by reverse genetics showed very similar properties to each other. This study showed, for the first time, that transplacental transmission of BTV-2, which had been minimally passaged in cell culture, can occur; hence such transmission might be more frequent than previously thought.