Periarteritis in experimental Border disease of sheep. II. Morphology and histochemistry of the lesion

Systemic Necrotizing Vasculitis in Sheep Is Associated With Ovine Herpesvirus 2

Ovine herpesvirus 2 (OvHV-2) is one of the gammaherpesviruses in the genus Macavirus that can cause malignant catarrhal fever (MCF) in ungulates. Sheep are the adapted host for OvHV-2 and it is generally assumed that infection is not associated with disease in this species. However, cases of "polyarteritis nodosa" or idiopathic systemic necrotizing vasculitis reported in sheep are similar to vascular lesions in clinically susceptible species with MCF. Using a recently developed in situ hybridization (ISH) method, we were able to identify OvHV-2 nucleic acids within lesions and correlate the viral distribution with systemic necrotizing vasculitis in 9 sheep, including both naturally and experimentally OvHV-2-infected animals. ISH, combined with polymerase chain reaction and histology, identify OvHV-2 as the likely agent responsible for sporadic, MCF-like vascular disease in sheep.

Acute pulmonary lesions in sheep experimentally infected with bovine viral diarrhoea virus

Six sheep, aged 6-8 months and seronegative for pestivirus, were inoculated intranasally, through the tracheal wall, and intrabronchially with a non-cytopathogenic isolate of bovine viral diarrhoea virus (ncpBVDV). Infected sheep were killed in pairs on post-inoculation day (PID) 2, 4 and 6. They all exhibited transient leucopenia or lymphopenia, or both. Platelet counts decreased but remained within normal limits. BVDV was isolated from buffy coats and tissues of all sheep inoculated with ncpBVDV but not from two uninfected control animals. Pulmonary lesions, evident in ncpBVDV-inoculated sheep, consisted of moderate oedema with multifocal alveolar septal necrosis and haemorrhage, infiltrates of mononuclear inflammatory cells, and degenerative changes in alveolar epithelium, endothelium and pulmonary intravascular macrophages. Additionally, there was morphological evidence of platelet activation and pulmonary intravascular macrophage stimulation. Lesions were not observed in the two control sheep.

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.

Cytotoxic T cell responses in lambs experimentally infected with Border disease virus

Mononuclear cells cytotoxic to a noncytopathic strain of Border disease virus (BDV) but not to uninfected cells were detected in the peripheral blood of experimentally infected lambs, 10 days after experimental infection, reaching peak levels of cytotoxicity 15 days post-inoculation. The specificity of the cytotoxic activity to BDV-infected cells was tested by including autologous targets infected with another virus (bovine respiratory syncytial virus, BRSV) and normal uninfected autologous targets. The cytotoxic T cells were virus-specific, as only autologous BDV-infected targets were lysed, whereas autologous targets infected with BRSV and uninfected targets were not lysed. The present results also suggest that the cytotoxic activity was largely MHC-restricted as the specific release from BDV-infected autologous targets was significantly higher than that of BDV-infected heterologous targets (P < 0.001) and the cytotoxicity against BDV-infected homologous targets was significantly reduced by the selective depletion of OvCD8+ T cells (P < 0.001).

Pathomorphological and immunohistological findings in progeny of goats experimentally infected with pestiviruses

A total of 25 pregnant goats without neutralizing antibodies against BVD virus were inoculated with two different pestivirus isolates at eight different stages of gestation. In both infection groups, various malformations were observed in fetuses and neonates. In three twins with neutralizing antibodies against BVD virus leukoencephalomalacia occurred, characterized by gelatinous transformation in the cerebral hemispheres. These lesions were comparable to alterations described in alternative pathology of Border disease in sheep. Although the immunohistological findings are characteristic for immunological tolerance and viral persistence, viable offspring persistently infected with pestivirus was not observed.

Pathogenesis of rheumatoid arthritis: a vascular hypothesis

Past research into the pathogenesis of RA has generally concerned itself with established inflammation. The present review summarizes alterations in microvascular anatomy and function which occur during the hypoxic state, in various experimental and disease conditions. It further shows that tissue hypoxia is a common finding in RA and that the microvascular alterations of RA are similar to those produced by experimental hypoxia. The available data suggest that microcirculatory compromise, concomitant with an increase in metabolic needs of synovial tissue, may initiate tissue injury via anoxia and acidosis, resulting in hydrolytic enzyme release, increased vascular permeability and acceleration of inflammatory processes. It is further believed that the microcirculatory abnormality may be generalized, accounting for the systemic manifestations often seen in RA. Factors effecting arteriolar blood flow obstruction are reviewed to identify areas for future investigation in RA and other disorders involving microvasculopathy. The multitude of longknown and newly recognized factors predisposing to vasospasm and vasodilatation have been outlined as a guide to possible mechanisms which may be operative in RA. An attempt has been made to gather and synthesize the available data in the hope that it may stimulate other investigators to pursue more definitive research into specific areas which may show early microvascular abnormalities in the pathophysiology of RA. Identification of factors operative early in the pathogenesis of RA, before it becomes self-perpetuating, may well be a step in the direction of preventing the ravages of this disease, or providing insight to more effective control.

The pathomorphology of malignant catarrhal fever. I. Generalized lymphoid vasculitis

A histologic, ultrastructural and immunohistochemical study of the vasculitis in the rete mirabile of 18 calves with experimental and two calves with spontaneous malignant catarrhal fevel showed lesions similar to those reported in graft rejection and some other lymphocyte-associated vasculopathies. The calves were examined at early, mid and late stages of clinical disease. Vascular lesions in the carotid rete were representative of those in other tissues examined. The magnitude of the arterial wall mononuclear cell infiltrate and the degree of arterial wall necrosis and degeneration increased with progression of the clinical disease. The predominant site of mononuclear cell accumulation was the adventitia. There was less medial and intimal involvement. The mononuclear infiltrate was composed of lymphocytes and macrophages with neutrophils and plasma cells rarely present. Endothelial hyperplasia, fibrinoid change and thrombosis were uncommon. Many changes contrasted with those recognized in an active Arthus reaction where adventitial change was minimal and most inflammatory cells were neutrophils or plasma cells. IgG and C3 rarely were detected in vessel walls with fluorescent antibody techniques. Serum immunoglobulins as measured by radial immunodiffusion were not elevated. Viral structures were not seen in tissues examined ultrastructurally.