Border disease virus infection of the newborn lamb

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.

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).

Lymphocyte responses to viral antigens and phytohaemagglutinin in persistently viraemic sheep and lambs experimentally infected with Border disease virus

Lymphocytes obtained from lambs 5 to 21 days after experimental infection with Border disease virus (BDV) showed significant blastogenic responses to live or inactivated BDV. Live virus stimulated significantly higher lymphocyte transformation (LT) responses than inactivated virus. Lymphocytes obtained from uninfected control and persistently infected lambs had no significant response to live or inactivated antigen. Lymphocyte responses to phytohaemagglutinin were significantly higher in control lambs than in experimentally infected lambs in samples obtained 5 to 10 days post-inoculation.

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.

Experimental pestivirus infections in newborn goat kids

Two experiments were carried out in which 37 healthy newborn goat kids were inoculated with a non-cytopathic ovine (BDV) or a cytopathic bovine pestivirus (BVDV) by intramuscular or intracerebral injection. No kids showed signs of disease or gross lesions which could be attributed to these viruses, but inoculated kids had lower mean growth rates than the controls. Significant histological changes in the CNS of 14 kids were restricted largely to the white matter and consisted mainly of hypercellular foci comprising microglial/histiocytic cells and mild perivascular infiltration by mononuclear cells. Varying degrees of infiltration of the myocardium by lymphocytes and plasma cells were observed. All kids remained negative for neutralizing antibodies against pestivirus until 2 to 3 weeks after infection. Titres increased during the following weeks. Pestiviruses were recovered from kids necropsied 10 days after inoculation, but not from any kids killed 20 days after inoculation or later. Non-cytopathic virus was isolated from various tissues of four kids that had received BDV and three kids that had been given BVDV. Cytopathic viruses were not recovered from any kids. Mean white blood cell counts in all kids were within the normal range at 4 and 8 weeks after inoculation. The lymphocyte response to stimulation by phytohaemagglutinin was significantly increased on both sampling occasions in the BDV-inoculated kids, while in the BVDV-inoculated animals, a similar increase was seen only at 8 weeks.

Border disease: effect of virus administered intracerebrally to newborn lambs

Six BVD antibody-free Dorset Horn lambs, less than 3-days-old, were infected by intracerebral inoculation of BD virus. Three of these lambs (Group I) were killed 7 days after inoculation (p.i.) and 3 (Group II) 21 days p.i. None of the lambs showed clinical signs of disease. Of the 5 lambs in which infection was established, 3 of Group I and 2 of Group II showed lesions of non-suppurative encephalitis. Although of varying severity and extent in individual animals, the lesions in all lambs appeared to be primarily of the same nature, with the cerebral white matter being the main target. BD virus was isolated from all lambs of Group I, killed 7 days p.i., but from none of Group II, killed 21 days p.i. Thus the induced BD infection appeared to be of a transient nature. The results indicate that the CNS of newborn lambs is capable of supporting BD virus replication with subsequent development of lesions. It is suggested that some of the cases of non-suppurative encephalitis of obscure aetiology occasionally encountered in young lambs in the field may be the result of infection with BD virus.