Experimental infection of fetal and newborn Suffolk sheep with scrapie virus

Fetal (n = 21) and newborn (n = 7) Suffolk sheep were inoculated with scrapie virus isolated from other Suffolk sheep. Twenty fetuses, 76 to 109 days of gestational age, were inoculated IM in the neck through the uterine wall and were examined for virus 47 to 322 days later by mouse inoculation. Scrapie virus was not detected before 254 days of age; only traces of virus were detected in 3 of 7 lambs examined thereafter (2 at 254 days of age and 1 at 322 days of age). Virus was limited to the supra-pharyngeal, prescapular, and mesenteric lymph nodes. Seven lambs were inoculated into the palatine tonsils with scrapie virus as newborns (3 to 12 days old) and were examined for virus when they were 147 to 210 days old. Virus was not detected in the lymphoreticular tissues or terminal portion of ileum of any lamb. Failure to find scrapie virus in these lambs and in most lambs inoculated as fetuses might indicate few had became infected. However, if most lambs and fetuses had become infected, the long zero phase of the infection could have accounted for failure to find scrapie virus in many of them examined too soon after inoculation. The limited findings of this study indicate that efforts to demonstrate prenatal or neonatal transmission of scrapie by detecting virus are hampered by the slowness of its replication.     

Experimental infection of pregnant ewes with bovine viral diarrhea virus type-2 (BVDV-2): effects on the pregnancy and fetus

The reproduction effects of bovine viral diarrhea virus type-2 (BVDV-2) infection were investigated in ewes inoculated with a non-cytopathic BVDV-2 isolate at three stages of gestation. Virus inoculation was followed by a transient viremia, accompanied by a transient and mild hyperthermia and nasal discharge in a few animals. Some ewes were sacrificed at different time-points after virus inoculation to study the kinetics of fetal infection. Infectivity and viral antigens were detected in placentomes from day 7 to 36 post-inoculation (pi) and in fetal fluids and tissues between days 10 and 28 pi. Cardiac petechial hemorrhages and hemoperitoneum accompanied by a severe fibrinous ulcerative placentitis were observed in fetuses examined at days 21, 28 and 36 pi. Inoculation of ewes at days 55-60 of gestation resulted in a prolonged virus replication in placentomes and fetal tissues; ewes that were allowed to proceed with pregnancy had 77% of abortions or fetal and perinatal deaths. Seven stillbirths, unviable and viable lambs born to these ewes were virus-positive at birth. Infectious virus was repeatedly isolated from leukocytes of two lambs up to 2 and 6 months of age, indicating they were persistently infected. Ewes inoculated at days 65-70 of gestation had 66.6% of fetal and perinatal losses. Three viable lambs born to these ewes were healthy, BVDV antibody-positive and virus-negative. A transient viral replication in placentomes and in a few fetal tissues, followed by the rise of fetal neutralizing antibodies and virus clearance was the result of inoculating ewes at days 120-125 of gestation. Lambs born to these ewes were healthy, antibody-positive and virus-negative. These results demonstrate that the biology of BVDV-2 infection in pregnant sheep is essentially similar to that of BVDV-1 in pregnant cattle and sheep. These features make this species an attractive animal model for studying the pathogenesis of congenital BVDV-2 infection.     

The effects of vaccination of Merino ewes with an attenuated Australian bluetongue virus serotype 23 at different stages of gestation

SUMMARY A cell culture attenuated Australian bluetongue virus serotype 23 (BLU23) prototype vaccine was assessed for its effects on pregnant Merino sheep. Seventy-six ewes were vaccinated at 5 different stages of gestation, and the failure to lamb at term was as follows: 35 to 43 days of gestation, 20/36 (56%); 57 to 64 days of gestation, 3/10 (30%); 81 to 88 days of gestation, 3/10 (30%); 109 to 116 days of gestation, 0/10 (0%); 130 to 137 days of gestation, 0/10 (0%). Of 30 ewes vaccinated with a cell culture supernatant fluid control between 35 and 43 days of gestation, 6.7% (2/30) failed to lamb at term. Two ewes vaccinated with BLU23 vaccine between 35 and 43 days of gestation had lambs with hydranencephaly. All other lambs born were clinically normal. Three ewes vaccinated with BLU23 aborted. Two of these were vaccinated between 35 and 43 days of gestation, the 3rd between 81 and 88 days of gestation. Five lambs were born with BLU group antibody. Four of these were from ewes vaccinated between 35 and 43 days of gestation, and 2 of these had hydranencephaly. The fifth was from a ewe vaccinated between 57 and 64 days of gestation. The vaccine did not produce disease in adult sheep, but was a potent cause of early foetal death and to a much lesser extent foetal malformation.     

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.     

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.     

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.     

Effects on ovine fetuses of exposure to ovine progressive pneumonia virus

Fetuses of 20 pregnant ewes at 4 gestational periods (45, 55, 85, and 100 days) were inoculated with ovine progressive pneumonia virus. Fourteen of 16 fetuses exposed to virus before gestational day 80 were either resorbed or expelled, whereas 10 of 15 fetuses exposed to virus after day 80 were normal at birth. Three of the 9 expelled fetuses and 1 of 2 newborn lambs had accumulations of lymphoid cells in the lungs. Virus was readily isolated from the tissues of expelled fetuses and newborn lambs. Lambs did not have precipitating antibody to the virus at birth, but 3 to 5 lambs had specific antiviral antibody at 18 months of age.     

Repetitive abortion in Neospora-infected ewes.

Pregnant ewes inoculated with cultured Neospora caninum tachyzoites in 1995, 1996, or 1995 and 1996 aborted or delivered weak or clinically normal lambs in 1996. Nine of 11 ewes in the study had previously produced infected lambs or fetuses after being experimentally infected in 1995. Fetuses and lambs produced in 1996 showed histologic lesions and zoites indicative of Neospora. Serologic responses and production of infected fetuses/lambs indicated systemic neosporosis in the ewes during gestation, although tachyzoites could not be cultured from maternal tissues. The repetitive infection of fetuses, and resulting clinical and histopathologic findings in the present study are similar to those reported in naturally infected cattle, adding to the already established similarities of neosporosis between sheep and cattle.     

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.     

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.     

Transplacental infection in mice inoculated with Getah virus

Transplacental transmission was demonstrated in pregnant mice subcutaneously inoculated with Getah virus. Viremia was shown in the infected dams, and high-titered virus was detected in the placenta and later in the fetus, suggesting virus invasion of the fetus through hematogenous infection of the placenta. High-titered virus was shown in the fetal brain and muscle and in the brain of the young dying soon after birth. Intrauterine infection resulted in a reduction of the litter size, number of young born alive and survival rate to 1 week of age. These results were further corroborated by necropsy performed several days after virus inoculation. The stage of gestation at the time of virus inoculation greatly influenced these results. Dams inoculated at 12 days of gestation delivered all dead babies, whereas virus inoculation at 5 days of gestation had no effect on the number of young born alive. The dams inoculated at 8 days of gestation had reduced litter sizes and those inoculated at 16 days of gestation produced slightly fewer live babies. Gestational stage at the time of virus inoculation also influenced viral growth in fetuses and placentas. The infection rate was low in dams inoculated at 5 days of gestation, high in dams inoculated at 8 or 16 days of gestation and 100% in dams inoculated at 12 days of gestation. High-titered virus was shown in placentas and fetuses of the dams inoculated at 8, 12 or 16 days of gestation. These results suggest that Getah virus may readily cross the placental barrier through hematogenous infection of the placenta in mice.     

Infection of bovine fetuses at 120 days' gestation with virulent and avirulent strains of bluetongue virus serotype 11.

Bluetongue virus infection in sheep and cattle during fetal development causes neuropathology. Two strains of bluetongue virus serotype 11 designated as UC-2 and UC-8 have different virulence patterns in newborn mice. These viruses have distinctly different electropherotype patterns on polyacrylamide gel electrophoresis indicating a genetic difference in these two viruses of the same serotype. Four bovine fetuses each were inoculated intramuscularly with either UC-2 or UC-8, and one fetus was inoculated with placebo. The inoculation was made intramuscularly through the uterine wall at 120 days' gestation, and the bovine fetuses were recovered by cesarean section 12 or 20 days after inoculation. Fetal blood was collected for virus isolation and serology. Virus was reisolated from brain, blood, lung and liver. Both strains, UC-2 and UC-8, cause severe lesions in the 120 day fetuses. The encephalomalacic lesions occurred earlier and were more severe in fetuses inoculated with UC-8 as compared to those inoculated with UC-2. The subtle differences observed in the fetuses inoculated with the two different strains suggest that there is a difference in pathogenic potential of the two viruses. These differences do not appear to be completely dependent upon the host species.     

Bluetongue virus serotype 20 infection in pregnant Merino sheep

Eleven maiden Merino ewes, free of antibody to bluetongue virus serotype 20 (BTV-20) in agar gel immunodiffusion and serum neutralisation tests, were mated once with a ram. Ten ewes were inoculated with BTV-20 35 to 42 days after service, and one ewe was left as an uninoculated control. One of the inoculated ewes and the control ewe remained uninfected throughout the experiment. Eight of the remaining 9 ewes showed clinical signs ranging from mild to moderate, and the other showed no clinical signs of infection. BTV-20 viraemia was detected in ewes between days 3 and 11 post inoculation, and the serum antibody response was followed. The control ewe and 5 of the 9 infected ewes were pregnant when examined 90 to 97 days after service. Each of these animals produced a normal lamb. There was no evidence of abortion in the remaining 5 ewes, and no transplacental transfer of virus was detected in the lambs of the 5 infected ewes. At necropsy, 46 days after the birth of the last lamb, no gross or microscopic lesions were observed in either the ewes or lambs.     

Clinical variations of border disease in sheep according to the source of the inoculum

Non-cytopathogenic pestivirus obtained from lambs with border disease, with or without nervous signs, was inoculated into pregnant ewes at 57 to 65 days of gestation. Live lambs born to inoculated ewes were clinically identical to the lambs from which virus was obtained, ie, either a hairy birth coat with central nervous system disturbance or a hairy birth coat without central nervous system disturbance.     

Ovine anaplasmosis: in utero transmission as it relates to stage of gestation

Seventeen mature, pregnant, anaplasmosis-susceptible and 3 anaplasmosis-carrier ewes were used in Anaplasma ovis in utero transmission studies. Susceptible ewes were arbitrarily allotted to 3 groups, 4 each in groups A and C and 9 in group B, and were inoculated with whole blood from a carrier ewe. Each group was Anaplasma-exposed once during one of the thirds of pregnancy. In all ewes, resulting parasitemias were low and anemias were mild. Three carrier ewes comprised group D. Blood samples were obtained once during gestation from each fetus at various stages of development for evaluation and inoculation into splenectomized lambs. Blood obtained from neonates before nursing was also evaluated for Anaplasma presence. Parasitemia was not detected in any fetus or neonate; however, 3 of 16 splenectomized lambs inoculated with fetal or neonate blood developed acute anaplasmosis. Dams of fetuses/neonates with infective blood had been Anaplasma-exposed during their 2nd or last 3rd of pregnancy. Infective Anaplasma agents crossed the placental barrier as early as 130 days of gestation.     

Pathology in the ovine foetus caused by an ovine pestivirus

Homogenised tissues or tissue culture supernatant fluid containing a noncytopathic pestivirus obtained from a lamb with a neurologic form of border disease, were inoculated into ewes at different stages of pregnancy. Foetal death occurred in 9 ewes of those inoculated between 19 and 47 days of pregnancy while 3 ewes did not lamb. Eight of the foetuses were aborted between 77 and 132 days of pregnancy; of these 6 were autolysed or mummified and one had arthrogryposis. The one full-term dead lamb had a hairy birth coat and lissencephalic micrencephaly. Foetal death occurred in only 7 of 14 ewes inoculated between 57 and 72 days of pregnancy. Four of these ewes aborted between 77 and 108 days of pregnancy and 3 gave birth to full-term, dead, hairy lambs. The remaining 7 ewes gave birth to live hairy lambs with severe inco-ordination. All lambs carried to term and aborted foetuses or lambs that could be examined had a range of intracranial malformations including focal leucomalacia, micrencephaly, hydranencephaly, porencephaly, lissencephaly and cerebellar hypoplasia. Some lambs also had skeletal abnormalities including arthrogryposis, scoliosis and brachygnathia inferior. The pestivirus isolate used in these trials produced more severe effects on the ovine foetus than previously observed in similar inoculation trials using pestivirus isolates from border disease lambs without nervous signs.     

The effects of bovine viral diarrhoea-mucosal disease (BVD) virus on the ovine foetus

Bovine viral diarrhoea-mucosal disease (BVD) virus has been incriminated as a cause of abortion, hairy birth coat and unthriftiness in sheep. Intravenous inoculation of 40 ewes 34 to 45 days pregnant with the V/TOB strain of virus produced death in two of four foetuses 9 days after inoculation and in all but one of 31 foetuses between 11 and 56 days. The highest levels of virus in placentomes and foetal tissues occurred between 9 and 15 days after inoculation and in foetal fluids between 11 and 18 days. Virus was not detected in any foetus later than 21 days after inoculation. Groups of 10 ewes infected between 59 and 62 days (Group B) and 70 and 76 days (Group C) of gestation had 73% and 62%, respectively, of abortions or perinatal foetal deaths. Birth weights of lambs born to infected ewes in groups B and C were significantly lower than those born to uninfected control ewes. Virus was recovered consistently from the cotyledons of the foetal membranes of live lambs, and irregularly from the tissues of full term foetuses that were dead at birth but on no occasion from mummified foetuses. There were no specific gross or microscopic lesions in tissues selected from aborted foetuses and the results highlight the difficulties associated with the diagnosis of BVD abortions and perinatal death of foetuses under field conditions.     

妊娠后期母羊饲粮营养水平对产后羔羊生长性能、器官发育和血清抗氧旨标的影响

本试验在干物质采食量一致条件下,改变精料补充料与饲草比例调控妊娠后期母羊饲粮营养水平,旨在研究其对产后羔羊生长性能、器官发育和血清抗氧化指标的影响.选用健康、年龄[(11.0±1.0)月龄]和体重[(44.43±2.20) kg]相近、妊娠90 d的怀双羔初产湖羊母羊66只,分为3组,每组22只.以干物质为基础按照精料补充料与饲草比例分别为5∶5(5∶5组)、4∶6(4∶6组)和3∶7(3∶7组)饲喂至产羔,产羔后各组母羊饲喂相同的全混合日粮,自由采食.出生10、60 d屠宰羔羊测定各组织器官重量,出生20、60 d采集羔羊血清测定血清抗氧化指标.结果表明:1)妊娠后期母羊饲粮营养水平对羔羊初生重、哺乳期(出生0～60 d)羔羊体重均无显著影响(P>0.05),但随营养水平降低,羔羊初生重有降低趋势(0.05≤P<0.10),出生40和50 d体重有增加趋势(0.05≤P<0.10).2)出生0d,随着妊娠后期母羊饲粮营养水平的降低,羔羊的胸深极显著提高(P<0.01),体斜长显著降低(P<0.05);出生60 d,随着妊娠后期母羊饲粮营养水平的降低,羔羊的胸深、曲冠臀长显著或极显著提高(P<0.05或P<0.01).3)出生10 d,羔羊的肝脏、肺脏的重量随妊娠后期母羊饲粮营养水平的降低而显著降低(P<0.05);出生60 d,各组羔羊的组织器官重量差异不显著(P>0.05).4)出生20和60 d,随着妊娠后期母羊饲粮营养水平的降低,羔羊血清中总抗氧化能力(T-AOC)、超氧化物歧化酶(SOD)活性、谷胱甘肽过氧化酶(GSH-Px)含量显著或极显著提高(P<0.05或P<0.01),丙二醛(MDA)含量极显著降低(P<0.01).妊娠后期通过精料补充料与饲草比例调控母羊饲粮营养水平时发现,低营养水平(低精料补充料比例)能够降低羔羊初生重,但经补偿生长作用,羔羊血清抗氧化能力得到提高,生长性能也得到恢复.     

A MUCOSAL DISEASE VIRUS INFECTION OF THE PREGNANT EWE AS A CAUSE OF A BORDER DISEASE-LIKE CONDITION

An experiment was designed to investigate whether a condition in Australian sheep with clinical and pathological similarites to Border Disease was caused by the infection of the pregnant ewe with a Mucosal Disease virus (MDV). Forty ewes, at 58 to 63 days after mating, were inoculated with material from lambs in which all, some or none of the tissues examined contained MDV. The clinical condition was observed only in lambs born to ewes inoculated with MDV-positive material and then only to ewes in the group which had serological evidence of MDV infection. It is concluded that the Border Disease-like condition in Australian sheep is caused by the infection of the pregnant ewe with a Mucosal Disease virus.     

妊娠后期母羊饲粮精料比例对羔羊生长性能、消化性能及血清抗氧化指标的影响

本试验旨在研究妊娠后期母羊饲粮精料比例对羔羊生长性能、消化性能和血清抗氧化指标的影响。试验选用66只妊娠90 d、平均体重为(44.45±2.20)kg的初产湖羊,按照体重相近原则随机分为3组,每组11个重复,每个重复2只。各组母羊妊娠期饲粮精料比例分别为50%、40%和30%,分娩后母羊饲喂相同的全混合日粮(TM R)。羔羊10日龄,每只母羊取1只羔羊断母乳,饲喂代乳粉;15日龄补饲开食料;20日龄补饲苜蓿干草,自由采食至60日龄。每10 d测定1次羔羊体重,51~60日龄进行羔羊消化代谢试验,20和60日龄采集羔羊血液测定血清抗氧化指标。结果表明:妊娠后期母羊饲粮精料比例对羔羊1、10、20、30、40、50、60日龄体重,20、60日龄体尺指标及营养物质表观消化率均无显著影响(P0.05)。随母羊饲粮精料比例降低,20日龄羔羊血清总抗氧化能力(T-AOC)、超氧化物歧化酶(SOD)活性极显著升高(P0.01),60日龄50%组显著或极显著低于其他2组(P0.05或P0.01);30%组20和60日龄羔羊血清谷胱甘肽过氧化物酶(GSH-Px)活性极显著高于其他2组(P0.01);血清中MDA的含量在20日龄时随母羊饲粮精料比例的降低而极显著降低(P0.01),60日龄时50%组显著高于30%组(P0.05)。结果提示,妊娠后期母羊饲粮的精料比例对产后早期断奶羔羊的体重、体尺、营养物质表观消化率无显著影响,但随母羊饲粮精料比例的降低,羔羊血清的抗氧化能力提高。