Infection of pregnant ewes with mucosal disease virus of ovine origin

Diversity among bovine pestiviruses

Bovine viral diarrhoea virus (BVDV) isolates are characterized by an important genetic, antigenic and pathogenic diversity. The emergence of new hypervirulent BVDV strains in North America has provided clear evidence of pathogenic differences between BVDV strains. The origin of BVDV diversity is related to high mutation rate occurring in RNA viruses but the consequences of mutations obviously depend on the genes which are involved. Mutations in genes encoding for structural proteins of immunological importance may have practical implications. Knowledge of BVDV diversity is important for understanding the wide variety of pathogenesis of diseases caused by the virus, for monitoring the epidemiology of the different types and for the design of optimum laboratory tests and vaccines. This review focuses on the origin and consequences of BVDV diversity with regard to pathogenesis, biotypes, and antigenic and genetic variations.

Bovine virus diarrhoea (BVD) control programme in an area in the Rome province (Italy)

A BVD control programme based on the identification and removal of persistently infected (PI) animals is being undertaken in an area in the Rome province, where BVD outbreaks had been previously detected. It involves 174 mainly dairy herds, from which blood samples of all bovines older than 1 year are obtained through the national brucellosis and leukosis eradication programme. Samples sufficient to detect the presence of seropositive animals at a prevalence of 5% or more are initially screened for antibodies against BVD virus (BVDV) using an immunoenzymatic assay. Upon identification of seroreagents additional blood samples are tested from the 6-12-month age category not included in the initial samples. Animals are considered immunotolerant if BVDV is demonstrated twice at a minimum 30-day interval. When no seropositive animals are detected during the first serological screening the herd is declared BVD-free if a second testing, preferably carried on the same animals previously tested, confirms the seronegative status of the herd. At present 147 farms have been tested, of which 63 (42.9%) are negative with respect to antibodies against BVDV. Of the 84 remaining herds in which one or more seropositives are detected, 13 are classified as recently infected. In eight of these recently infected herds, 22 PI animals have been identified.

Distribution of viral antigen in uterus, placenta and foetus of cattle persistently infected with bovine virus diarrhoea virus

The tissue distribution and cellular localisation of bovine virus diarrhoea virus (BVDV) was investigated in the uterus, placentomes, intercotyledonary foetal membranes and foetal organs of three persistently infected (PI) pregnant heifers. The uterus and ovaries of a non-pregnant PI heifer were also included in the study. Cryostat sections were examined using immunohistochemical techniques and monoclonal antibodies against BVDV. A double immunofluorescence technique was used to identify BVDV positive cells that also showed staining for either the leukocyte common antigen CD45 or the cytoskeletal filament vimentin. BVDV antigen was detected in all the organs examined, and was present in both epithelial and non-epithelial cells. In all organs many of the virus-positive cells also showed reactivity for vimentin. In the foetal liver and spleen a small, scattered population of virus-positive cells showed reactivity for CD45. A few cells showed reactivity both for BVDV antigen and for CD45 in the placentomes and intercotyledonary foetal membranes. In contrast to earlier reports, only scattered cells in the foetal part of the placentomes, the cotyledons, showed reactivity for BVDV antigen. However, in the chorion of the intercotyledonary foetal membranes, a larger proportion of the trophoblast cells showed reactivity for BVDV, especially the binuclear trophoblast cells. In the uterus, pregnancy appeared to favour virus replication, as the section from the pregnant heifers showed much stronger staining and a higher proportion of viral antigen-positive cells than sections from the non-pregnant PI heifer.

Epidemiology of bovine viral diarrhea virus

Prevalence studies around the world show that BVDV is widespread in most cattle raising countries. There are significant differences, however, in prevalence between areas, probably the result of differences in cattle population structure and management practice. Direct contact with PI animals is probably the most important method of transmission of infection; however, field studies have shown that some limited spread of infection also occurs in the absence of PI animals. This may be due to contact with acutely infected animals or contact with other species infected with BVDV. Different ways of indirect transmission such as contaminated needles and equipment have been proven experimentally, and indirect transmission is considered to have some importance. If a PI animal is introduced directly into a dairy herd, most animals will be infected within a few months. On many occasions, however, a herd gets infected by other means than direct introduction of PI animals. In these cases, the infection is often spread to only a few animals after which the infections stops. The infection is then reinforced when PI animals are born. Slow and hence prolonged spread of infection in herds without PI animals also has been described, but the mechanism is not fully understood. Family lines of PI animals delivering PI calves are fairly common and can cause the infection to continue for several years. The clinical manifestations, acute BVDV, reproductive disorders, birth of malformed, weak and undersized calves, unthrifty PI animals, and mucosal disease often appear within certain periods. Large variation, however, can occur between herd outbreaks due to variation in virulence of the BVDV strain, housing of the cattle, and variation in transmission patterns. The extensive transmission of infection from PI animals makes different surveillance methods possible. Thus testing of a screening sample of a few young stock of antibodies and determination of antibody titer in bulk milk will often give good indication of presence of PI animals in herds not using BVDV vaccines. In herds using killed vaccine, determination of antibody titers among few young stock can show the presence of PI animals. The high incidence of infection combined with all the different damages that are seen after BVDV infection cause huge economical losses, which on a national level in the UK and Denmark (i.e., areas with widespread occurrence of infection) has been calculated as between 7 and 27 million pounds (between $11 and $42 million) per million calvings. Epidemiologic studies are important as a basis for selection of control strategy. Because of the variation in epidemiology between geographic areas, evaluation of a control strategy in an area preferentially should be based on epidemiologic studies in the same area.

Border disease in sheep

The current knowledge on border disease in sheep is reviewed. This is a congenital and teratogenic disorder induced by pestivirus. The history, etiology, epidemiology, clinical aspects, and pathologic lesions at postnatal and intrauterine infections (as well as in congenitally affected animals), pathogenesis, immunity, diagnosis, and control and prevention of the syndrome are discussed.

Variation in neuropathogenicity in sheep fetuses transplacentally infected with non-cytopathogenic and cytopathogenic biotypes of bovine-virus diarrhoea virus

Pregnant Merino ewes were inoculated intravenously between days 63 and 65 of gestation with a non-cytopathogenic (ncp) bovine-virus diarrhoea-virus (BVDV) isolate (experiment A). The histomorphological findings and the distribution of viral antigen, as revealed by immunohistochemistry in brains of fetuses from experiment A, were compared with those seen in fetal brains from a previous study (experiment B), in which pregnant ewes had been intravenously infected between days 65 and 68 of gestation with the cytopathogenic (cp) BVDV strain Indiana. The two viruses showed remarkable variations concerning their pathogenicity for the developing fetal brain. The cp BVDV had a much higher neuropathogenic potential than the ncp BVDV and induced severe intracranial malformations in most fetuses. In experiment A, exclusively relatively mild leucoencephalomalacic lesions occurred. Between fetuses of the two experiments, significant differences concerning the distribution of viral antigen and the inflammatory response were found. In the majority of fetal brains from experiment B examined at days 10, 14 and 21 post inoculation (p.i.), antigen-containing differentiated brain cells (neurons, astrocytes, oligodendrocytes) and undifferentiated cells in the periventricular germinal zones were seen throughout the different zones of the developing telencephalon and cerebellum. At 21 days p.i., a marked inflammatory response consisting of brain macrophages and other mononuclear cells occurred in the meninges and in the brain parenchyma of fetuses from experiment B. In brain sections of fetuses infected with ncp BVDV, in contrast to fetuses infected with cp BVDV, viral antigen was not detectable during the early stages (days 10 and 20) p.i., and histopathological lesions were not seen at this stage. At days 41 and 47 p.i., antigen-positive astrocytes and oligodendrocytes were found in the developing white matter of the telencephalon and cerebellum. Furthermore, antigen-containing neurons were seen in the developing cerebral cortex. Cellular infiltrations in fetal brains from experiment A were limited to the leucoencephalomalacic areas in the developing cerebral and cerebellar white matter and consisted exclusively of brain macrophages. Immunohistochemical staining in brain sections of fetuses from both experiments revealed that numerous perivascular cells contained viral antigen, whilst positive endothelial cells were exclusively found in fetuses from experiment A. From the findings of this study it was concluded that the cp BVDV stain used in experiment B has a marked tropism for the fetal brain and both its already differentiated and undifferentiated cell populations, and that the resulting brain lesions primarily are the consequence of a direct cytolysis of these cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Ruminant pestivirus infections in animals other than cattle and sheep

The current knowledge on infection with ruminant pestiviruses in animals other than cattle and sheep and reviewed. Natural infection is found to occur in goats, in captive and free-living ruminants, as well as in pigs. The viral agent, susceptible species, epidemiology, clinicopathologic lesions, pathogenesis, diagnosis, control, and consequences for control programs in domestic ruminants are discussed.

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 (BVDV) 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--not 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.

Virological and pathological findings in sheep fetuses following experimental infection of pregnant ewes with cytopathogenic-bovine-virus diarrhoea virus

Eighteen pregnant Merino ewes were inoculated intravenously between days 65 and 68 of gestation with the unpurified cytopathogenic (cp) bovine virus diarrhoea virus (BVDV) strain Indiana (experiment I). In experiment II, three ewes were inoculated with the same virus after two successive plaque isolations in order to compare its pathogenicity for the fetus with special regard to lesions in the fetal brain. In experiment I, fetal blood and tissue samples, allantoic fluids and placentomes were collected sequentially between 10 and 80 days post-inoculation (p.i.). BVDV was recovered from 6 of 19 fetuses examined during the first 3 weeks after inoculation. From fetuses sampled between 30 and 50 days p.i. virus was isolated from three cases only, and from 60 days p.i. onwards virus was no longer recovered. BVDV was longer detected in the allantoic fluid than in fetal tissues and continued to be present until 80 days post-inoculation. From tissue samples of two fetuses of experiment I, only non-cytopathogenic BVDV was isolated, whilst samples from seven fetuses contained the cp BVDV biotype as revealed by an immunoplaque assay. The cp biotype was also isolated from placentomes. In experiment II, virus was not isolated from any of the tissue samples of two living fetuses collected at 67 days post-inoculation. In both experiments, cp BVDV was recovered from allantoic fluid samples. In contrast to the developing fetal brain, other tissues or organs seemed to be less vulnerable to the cp BVDV strain Indiana. The partial purification of this virus strain did not affect its pathogenicity for the brains of the developing fetuses.

Experimental pestivirus infections in pregnant goats

Fifty pregnant goats, inoculated intramuscularly at different gestational stages with a non-cytopathic ovine pestivirus or a cytopathic bovine pestivirus, all developed pestivirus-neutralizing antibodies within 5 weeks of inoculation. The incidence of reproductive failure was similar for the two agents. Parturition at term with only healthy kids occurred in 13 (26 per cent) of the goats. Viable kids were not born to any of the 17 goats inoculated at about day 40 of gestation. Three of the 17 delivered dead or weak kids, seven aborted and three of seven which were necropsied during pregnancy had markedly underdeveloped and autolysed or mummified fetuses in utero, while four were barren. When inoculated at around the 60th day of gestation, two of 18 animals gave birth to only healthy kids, 12 to dead and/or weak kids, two aborted and, at necropsy, a small, decomposed fetus was found in one goat while one other was barren. In this group, one kid was ataxic and seven others had body tremors characteristic of border disease. One of the latter kids was viable. Of 15 goats inoculated at around day 100 of gestation, 11 gave birth to healthy kids only, three to dead and/or weak kids and one aborted. In 23 progeny, histological changes in the central nervous system (CNS) consisted mainly of cerebral white matter necrosis, cerebellar dysplasia, hypercellular areas in white matter and lymphocytic perivascular cuffings. All seven weak-born kids with signs of border disease had CNS lesions, particularly cerebellar dysplasia and/or hypercellular areas. Non-cytopathic pestivirus was isolated from tissues from all eight progeny examined in the 40-day inoculation group, from tissues and/or serum from 10 of 23 progeny in the 60-day group, and from four of 24 in the 100-day group. Persistent infection was demonstrated in a healthy kid, in a viable shaker and in two other kids which appeared normal at birth. Examination of offspring before ingestion of colostrum revealed pestivirus antibodies in one kid in each of the 40- and 60-day inoculation groups and in five kids in the 100-day group.

Outbreaks of border disease in goats induced by a pestivirus-contaminated orf vaccine, with virus transmission to sheep and cattle

Five herds with a total of 276 female goats experienced severe outbreaks of reproductive failure due to a pestivirus-contaminated experimental orf vaccine given early in the breeding season. The reproductive failures comprised barrenness in 42 goats, abortion in 53 and, in 118, the birth of dead or weak kids. The incidence of female goats with such failures was 82 per cent overall, herd incidence rates ranging from 79 to 96 per cent. No progeny showed characteristic signs of border disease (BD). Microscopic lesions in the CNS were moderate, mostly characterized by hypercellularity, cell disorganization and decreased myelin content. Non-cytopathic strains of pestivirus were demonstrated in tissue or serum from two weak-born and two apparently healthy kids. Neutralizing antibodies against a bovine pestivirus were found in all 254 goats examined about 4 months after vaccination. At the end of the breeding season, all kids were removed and 74 young kids were introduced from presumably normal herds. Approximately 8 months later, 64 (86 per cent) of the bought-in kids had pestivirus antibodies. Two years after the outbreaks, such antibodies were found in all but three of 127 vaccinated goats still alive, and another 2 years later, in all 22 vaccinated goats in one of the herds. Sheep also were kept on the same five farms and cattle on one. Sheep in two of the flocks showed reproductive failure probably caused by pestivirus transmitted from infected goat offspring. A pair of twin lambs showed nervous signs and brain lesions characteristic of BD, while 17 other lambs had a very low growth rate. Virus was not isolated from any lamb. The prevalence rates of ewes with pestivirus antibodies in the two affected flocks were 33 and 72 per cent, respectively. One of nine cows aborted a pestivirus-infected foetus, and all were antibody-positive.

Serologic examination of aborted ovine and bovine fetal fluids for the diagnosis of border disease, bluetongue, bovine viral diarrhea, and leptospiral infections

Fetal serum from most of 994 bovine and 553 ovine aborted fetuses was tested serologically for antibodies to border disease (BD), bovine viral diarrhea (BVD), and bluetongue (BT) viruses, and to Leptospira sp., and the results were compared with the results of isolation procedures, fluorescent antibody tests (FAT), and histologic examinations of the same fetuses. Antibodies to BT virus were not found in any of the 994 bovine and 553 ovine fetuses. Antibody titers to BVD virus were present in 39 of 966 bovine fetuses tested, and BVD virus was detected in 4 of the 39. Four of 74 fetuses in which the BVD virus was detected by FAT or isolation had titers to BVD virus. Microagglutination (MAT) titers to 1 or more of 5 serovars of leptospires were present in 52 of 773 bovine fetal sera tested. Leptospires were not detected by FAT in any bovine fetuses that had leptospiral antibody titers. Leptospires were detected by FAT in 15 aborted calves, and none of these had MAT titers. Antibody titers to BD virus were present in 80 of 486 fetal lamb sera tested, and the virus was detected by FAT or isolation in 3 of the 80 fetuses. Border disease virus was detected in 14 of 486 fetal lambs tested. Twelve of the 14 were tested serologically and 3 had titers to BD virus. Leptospiral antibody titers were present in 27 of 326 ovine fetal sera tested. Leptospires were not detected in any of the 326 ovine fetuses tested by FAT.

Effect of bovine virus diarrhoea virus on pregnancy in the ewe monitored by ultrasound scanning and levels of 15-keto-13,14-dihydro-PGF2 alpha and progesterone

Fourteen unvaccinated and seronegative ewes were experimentally infected with bovine virus diarrhoea virus around day 60 of pregnancy. Two other groups of pregnant ewes served as control animals. The animals were followed with ultrasound scanning to study the status of the fetus and with frequent blood sampling for analysis of progesterone and 15-keto-13,14-dihydro-PGF2 alpha, two hormones that could reflect the propagation of the infection. The unvaccinated ewes responded to the infection with abortion, resorption of the fetus, mummification or no changes at all. The endocrinological changes reflected in a most adequate way the pathological changes in the uterus. Detailed endocrinological studies can contribute to the understanding of the pathogenesis of some infectious diseases that affect reproduction.

A survey of hairy shaker disease (border disease, hypomyelinogenesis congenita) in sheep

A survey by mail in 1979 of 995 sheep farmers in Victoria enquiring as to the occurrence of hairy shaker disease (HSD) in lambs on their farms resulted in a 48% response. A total of 17 farms reported the presence of HSD. One hundred and eleven ewes produced lambs with HSD representing a small proportion only of the ewes (0.8%) on these farms and an even smaller percentage of the total ewes (0.03%) in the survey. Abortions were not prevalent on the majority of farms reporting HSD. There was no evidence that HSD was more common in any particular area in Victoria. As was anticipated mucosal disease virus/bovine virus diarrhoea (MDV) antibody was often present in serums from affected sheep. It was concluded that at present, the hairy shaker form of border disease did not appear to be an economically important problem in Victoria.

Congenital infections with nonarbo togaviruses

The present review deals with the similarities and differences of selected aspects of prenatal pestivirus infections of domestic animals and congenital rubella of man. Hog cholera virus, bovine virus diarrhoea virus and border disease virus are antigenically closely related, but unrelated to rubella virus. The nonarbo togaviruses are capable of producing congenital infections resulting in a wide spectrum of abnormalities. The infected foetus can die in utero, in the neonatal period, or it may be born with teratogenic defects. In addition, apparently healthy progeny can be delivered that develop a late onset disease, months, or years after birth, or remain clinically normal for life. The ultimate outcome of a congenital infection is mainly determined by the stage of foetal development, at which infection occurs. Foetuses exposed to rubella virus raise an antibody response to the virus, whereas domestic animals frequently fail to respond immunologically to a congenital pestivirus infection. In congenital rubella the virus usually disappears from the host's body 1-2 years after birth. However, congenital pestivirus infections may be characterized by a lifelong and widespread persistence of virus in clinically healthy animals. Such animals are of significance in the epizootiology of bovine virus diarrhoea, border disease or hog cholera.

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.

Experimental infection of Nigerian sheep and goats with bovine virus diarrhoea virus

Apart from leucopenia and a low grade pyrexia Nigerian goats showed no ill effects following inoculation with bovine virus diarrhoea virus. Sheep showed a variable leucopenia without pyrexia. No difficulty should arise in differentiating BVD infections from peste des petits ruminants.

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.