Viral persistence and abnormalities of the central nervous system after congenital infection of sheep with border disease virus

Investigation into an outbreak of Border disease virus in pigs in England

Border disease (BD) was first reported in 1959 in lambs from the border region of England and Wales. The causative virus (BD virus; BDV) has since been identified in several other ruminant species and pigs. The virus is prevalent in sheep flocks of UK, Europe and USA and has potential to inflict substantial economic losses. Natural BDV infection of pigs was first reported in the UK in 1992 from pigs with haemorrhagic lesions and more recently from healthy pigs in Spain and Japan. Here, a persistent problem of poor growth and anaemia in a small proportion of growing pigs on a mixed pig and sheep holding was investigated and tissues were tested in a pan viral microarray. The microarray detected BDV RNA in several tissues which was further confirmed by sequencing, specific BDV PCR and immunohistochemistry. Phylogenetically, the virus clustered with other BDVs in the sub‐genotype 1b. This investigation highlights likely interspecies transmission of pestiviruses and their impact on pestivirus detection and eradication programs.

Concurrent Peste des Petits Ruminants Virus and Pestivirus Infection in Stillborn Twin Lambs

Concurrent infection with peste des petits ruminants virus (PPRV) and pestivirus was diagnosed in stillborn twin lambs. With the flock history, the findings of epidermal syncytial cells and necrotizing bronchitis/bronchiolitis prompted testing for PPRV infection, and PPRV antigen was detected by immunohistochemistry (IHC) in the skin, lungs, kidneys, rumen, and thymus. Macroscopic anomalies that were typical of border disease included scoliosis, brachygnathism, prognathism, arthrogryposis, hydranencephaly, cerebellar hypoplasia, and hairy fleece; pestiviral antigen was detected by IHC in the brain, liver, lungs, and kidneys. Tissues from both lambs were positive by reverse transcriptase-polymerase chain reaction (RT-PCR) for PPRV and pestivirus. To the authors' knowledge, PPR has not been reported previously as a congenital infection or in combination with pestiviral infection.

Absence of pestivirus antigen in brains with white matter damage

We previously suggested that antenatal pestivirus infection might play a role in the pathogenesis of perinatal brain white matter damage (WMD) in preterm infants. We have now examined 22 brains from stillborns and deceased newborns (both preterm and term) for the presence of bovine virus diarrhoea virus (BVDV) antigen. The brains of five females and five males with WMD (median gestational age 36.5wks), and nine female and three male controls (median gestational age 36.5wks) were used in the study. No BVDV antigen was detected in any of the 22 brains. We conclude that brain infection with BVDV is unlikely to play a role in WMD pathogenesis among preterm or term newborns. Further research is needed to test the hypothesis that intrauterine exposure to pestivirus antigen elicits a fetal inflammatory response which then contributes to WMD.

Distribution of Border disease virus antigen in lymphocyte subpopulations in the peripheral blood of experimentally infected lambs

Ten lambs were experimentally infected with Border disease virus and the distribution of viral antigen in lymphocyte subpopulations studied by flow cytometry. The virus was isolated in culture from the peripheral blood mononuclear cells (MNC) of all experimentally infected lambs for a mean period of 9.8 +/- 1.03 days. The peak virus titre of 3.26 log10 TCID50 per 10(6) MNC was attained Day 9 post-inoculation (pi). Viral antigen was present in peripheral blood lymphocytes of experimentally infected lambs as early as 24 h pi and continued to be detected up to Day 10 pi. The number of lymphocytes expressing viral antigen rose from 12.38 +/- 1.22% in samples taken Day 3 pi to 23.21 +/- 2.82% on those collected Day 7 pi, dropping gradually thereafter. During the peak period of infection, 12.46 +/- 2.09% of B cells, 37.71 +/- 10.96% of T cells and 52.33 +/- 8.27% of lymphocytes which were neither B nor T lymphocytes expressed viral antigen. Most of the infected lymphocytes expressed the OvCD5 (T cell) molecule. The virus affected all T cell subsets but the suppressor/cytotoxic (OvCD8+) cells appeared to be the main targets. During the peak period of infection, 54.20 +/- 6.16% of the infected T cells expressed the OvCD8 molecule, 31.58 +/- 7.12% were OvCD4+, and 12.67 +/- 6.50% were OvWC1+ (T-19+, gamma/delta).

Replication of border disease virus in ovine lymphocytes and monocytes in vitro

Adherent and non-adherent mononuclear cells obtained from the peripheral blood of normal sheep supported the in vitro replication of a non-cytopathic and a cytopathic strain of Border disease virus (BDV) with no apparent cytopathic effects. There was a significant rise in virus titres in adherent mononuclear cells (monocyte) and non-adherent (lymphocyte) cultures infected with both non-cytopathic and cytopathic strains of BDV 24 hours after inoculation. Peak virus titres of 5.36 log10 TCID50 ml-1 were recorded in adherent samples incubated for 48 hours while peak titres of 6.17 log10 TCID50 ml-1 were recorded in lymphocyte culture after 72 hours of incubation. Both the non-cytopathic and the cytopathic strains of BDV produced significantly higher titres in non-adherent (lymphocyte) cultures than in adherent (monocyte) cultures (P < 0.001) but the replication in adherent cells was faster than in nonadherent cell cultures. The addition of virus on both types of mononuclear cell cultures had no effect on cell viability but it had a significant inhibitory effect on the blastogenic responses of lymphocytes to phytohaemagglutinin.

Effects of congenital infection of sheep with border disease virus on myelin proteins

Border disease (BD) of sheep is caused by a virus in the genus Pestivirus that results in decreased myelination throughout the CNS when acquired congenitally. Pregnant ewes were inoculated with BD virus at 50 days of gestation, and myelin proteins were quantified in several regions of the CNS during prenatal and postnatal development of infected lambs for comparison with age-matched controls. Newborn field-infected lambs were also examined. Myelin basic protein (MBP), proteolipid protein (PLP), myelin-associated glycoprotein (MAG), and 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP) were measured by densitometric scanning of western blots. Deficiencies in the myelin proteins were detected as early as 116 days of gestation, and the deficiencies of myelin proteins were most pronounced in the cerebellum at all ages examined. PLP and MBP increased from 10-30% of normal in cerebellar white matter at birth to 40-60% of normal at 6 months, suggesting some catch-up in the amount of compact myelin with development. MAG and CNP were between 70 and 80% of control levels in the cerebellum at birth and at 6 months. Similar results were obtained for the corpus callosum and spinal cord of infected lambs, but the deficiencies of myelin proteins were not as great. A common finding in all regions examined was that MBP and PLP were reduced more than MAG and CNP. This is probably explained by a greater deficit of compact myelin, in which MBP and PLP are localized, than of associated oligodendroglial membranes, in which MAG and CNP are concentrated.(ABSTRACT TRUNCATED AT 250 WORDS)

Myelin-associated glycoprotein (MAG) in myelin deficiency of caprine beta-mannosidosis

Caprine beta-mannosidosis is an inherited lysosomal storage disorder due to a deficiency of beta-mannosidase which cleaves beta-linked mannose residues from the ends of N-asparagine linked oligosaccharides of glycoproteins. Histological and chemical examination has revealed a deficiency of compact myelin in the brains and spinal cords of affected goats. Since myelin-associated glycoprotein (MAG) is glycosylated and its metabolism could be directly affected in this disease, we investigated the possibility of a differential treatment of MAG in caprine beta-mannosidosis in comparison to non-glycosylated myelin proteins. MAG, myelin basic protein (MBP), 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP), proteolipid protein (PLP) and glial fibrillary acidic protein (GFAP) were quantified by western blot analysis in whole homogenates of spinal cords and hemispheres from affected goats at 1, 3 and 6 days of age and from normal controls. The yields of isolated myelin from the spinal cords of affected goats varied from 37 to 63% of normal and were 7% or less of normal from the hemispheres. In mutant spinal cords, the deficits of MAG, CNP and PLP measured in whole homogenates corresponded reasonably well with the decreased myelin yields, but the levels of MBP were consistently much closer to control levels than those of the other myelin proteins. A greater deficiency of PLP than MBP was also apparent in the myelin fractions purified from the affected spinal cords. In homogenates of mutant hemispheres, MAG, MBP, PLP and CNP were undetectable or at trace levels in comparison to controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Border disease of sheep: the disease in the newborn, adolescent and adult

Border disease (BD) is a condition of newborn sheep that results from congenital infection by a non-cytopathic pestivirus occurring during the first half of gestation. The expression of the virus is largely determined by the age of the fetus at the time of infection, producing four distinct disease syndromes: (1) early embryonic death, (2) abortion and stillbirth, (3) birth of lambs with malformations, and (4) birth of small, weak lambs, lacking characteristic clinical signs, but bearing features of immunosuppression. The effects of the virus infection during the developmental stages of the fetus are most apparent as distinctive clinical signs at the time of birth but a state of specific immuno-tolerance with associated virus persistence remains for the lifetime of the sheep. Although the clinical signs disappear with time, some effects of virus persistence may continue into adolescence and often into adulthood. Characteristic lesions are found in the nervous, endocrine, skeletal and integumentary, and immune systems.

Cell phenotypes in the efferent lymph of sheep persistently infected with Border disease virus

The prefemoral efferent lymphatics of sheep persistently infected (PI) with Border disease virus (BDV) were cannulated in order to study the effects of the virus on cells of the immune system. Efferent lymphocytes recovered from PI sheep were phenotyped using a panel of monoclonal antibodies (MoAb) specific for ovine cell-surface markers and compared to lymphocytes recovered from normal, healthy controls. PI sheep had an increased percentage of cells expressing the T cell-associated molecules CD5, CD4, CD8 and T19, also an increase in cells expressing CD1 and a population of cells expressing low levels of the T19 molecule which was not present in control sheep. The lymphocytes were examined for the presence of BDV using virus-specific MoAb. On average 8.5% of the efferent lymphocytes from PI sheep carried virus antigen. BDV antigen was also found in the mononuclear cells and connective tissue of lymph nodes indicating widespread virus dissemination within the lymphoid system of PI sheep.

Exclusion of infectious diseases from sheep and goat farms

It is important for practitioners and owners to be aware of the risk associated with an open herd. This article has discussed some of the infectious diseases that might be inadvertently introduced. Many others--including most exotic diseases and some that are regulated by governmental agencies, such as tuberculosis and brucellosis--have been omitted. It should be obvious that a simple health certificate is an inadequate guarantee of freedom from infections. Instead, producers should be prepared to invest both time and money in evaluating the health status of the herd of origin. Some of the diseases discussed, such as foot rot, cause tremendous financial losses. Others, such as pinkeye, can be easily "lived with." The point to be made is that producers should consider all these and other diseases and then make informed decisions based on the probable cost of these diseases if they became established in the herd.

Alterations in lymphocyte subpopulations in peripheral blood of sheep persistently infected with border disease virus

Fourteen sheep persistently infected with border disease virus were investigated to examine the effects of persistent viraemia on lymphocyte subpopulations in peripheral blood and their responses to the mitogen phytohaemagglutinin (PHA) in vitro. Persistently infected sheep had significantly more CD8+ (cytotoxic-suppressor) T-lymphocytes than uninfected sheep of the same age (P less than 0.001). The total number of CD4+ (helper) T-lymphocytes were not significantly different but there were more T-lymphocytes (CD5+) which were CD4- and CD8- in normal sheep than persistently infected sheep (P less than 0.001). Peripheral lymphocytes obtained from persistently infected sheep showed significantly reduced blastogenesis induced by PHA than those obtained from normal sheep (P less than 0.001).