Post-viraemic detection of bovine ephemeral fever virus by use of autogenous lymphoid tissue-derived bovine primary cell cultures.

BACKGROUND: The potential tissue replication sites and specific cell types that support in vivo virus survival beyond the acute phase of bovine ephemeral fever virus (BEFV) infection have not been fully defined in cattle. To clarify the knowledge gap, tissue specimens were tested after collection from an adult steer necropsied 1 week after acute BEF. CASE REPORT: Significant necropsy findings included fibrinoproliferative synovitis in the stifle joints and fibrin clot-laden fluid in serous body cavities. Moderate numbers of infiltrating neutrophils were demonstrated in sections of the prefemoral lymph nodes and haemal node, and lymphoid hyperplasia in the spleen, haemal node and prefemoral lymph nodes. Viral RNA was detected by qRT-PCR in fresh spleen, haemal node, prefemoral lymph node, synovial fluid and in several spleen-derived cell cultures. BEFV was isolated from autogenously derived splenic primary cell cultures 6 days after cessation of viraemia, and characteristic bullet-shaped virions were confirmed by electron microscopy of an ultrathin haemal node section. In sections of the spleen, haemal node and other tissues, immunohistochemistry demonstrated BEFV antigens that were intracellularly associated with probable histiocytic cells. CONCLUSION: BEFV has preferential tropism for bovine lymphoid tissues and the spleen and haemal node may be potential sites for post-viraemic virus replication.

Viral neurotropism, peripheral neuropathy and other morphological abnormalities in bovine ephemeral fever virus-infected downer cattle.

OBJECTIVE: This study assessed the neurotropism of bovine ephemeral fever (BEF) virus (BEFV) and described histomorphological abnormalities of the brain, spinal cord and peripheral nerves that may causally contribute to paresis or paralysis in BEF. METHODS: Four paralysed and six asymptomatic but virus-infected cattle were monitored, and blood and serum samples screened by qRT-PCR, virus isolation and neutralisation tests. Fresh brain, spinal cord, peripheral nerve and other tissues were qRT-PCR-tested for viral RNA, while formalin-fixed specimens were processed routinely and immunohistochemically evaluated for histomorphological abnormalities and viral antigen distribution, respectively. RESULTS: The neurotropism of BEFV was immunohistochemically confirmed in the brain and peripheral nerves and peripheral neuropathy was demonstrated in three paralysed but not the six aneurological but virus-infected animals. Wallerian degeneration (WD) was present in the ventral funicular white matter of the lumbar spinal cord of a paralysed steer and in cervical and thoracic spinal cord segments of three paralysed animals. Although no spinal cord lesions were seen in the steer euthanased within 7 days of illness, peripheral neuropathy was present and more severe in nerves of the brachial plexuses than in the gluteal or fibular nerves. The only steer with WD in the lumbar spinal cord also showed intrahistiocytic cell viral antigen that was spatially distributed within areas of moderate brain stem encephalitis. CONCLUSION: The data confirmed neurotropism of BEFV in cattle and documented histomorphological abnormalities in peripheral nerves and brain which, together with spinal cord lesions, may contribute to chronic paralysis in BEFV-infected downer cattle.

Three-day fever.

Three-day fever is a viral disease caused by an Ephemerovirus of the family Rhabdoviridae, transmitted by arthropod vectors. It is common in tropical and sub-tropical regions, where it affects mainly domestic cattle and buffaloes, especially in intensive dairy or fattening production systems. It is of economic importance because it reduces milk production and fertility and causes abortion. The disease is generally benign. It manifests in several susceptible subjects simultaneously, with a sudden episode of fever accompanied by muscle involvement with arthritis, stiffness of the limbs, and lameness, followed by rapid recovery. The presence of a serofibrinous exudate in the joints is indicative of the disease. Clinical diagnosis is often difficult in the absence of pathognomonic signs. Epidemiological factors (proliferation of arthropod vectors), associated with a short-lived fever and the presence of many immature neutrophils, point strongly to three-day fever. In the absence of any specific treatment, the symptoms are treated with antibiotics and anti-inflammatories. Medical prophylaxis currently uses live attenuated vaccines, pending the development of recombinant vaccines, which are giving promising results.

Demonstration of vascular permeability changes in cattle infected with bovine ephemeral fever virus.

Five cattle infected with bovine ephemeral fever virus were necropsied on the day after onset of clinical disease, when clinical signs of lameness were most severe. Gross lesions observed included a serofibrinous polyserositis involving the synovial, pericardial, thoracic and abdominal cavities. The associated histological changes consisted primarily of oedema and an influx of neutrophils into affected tissues and fluids. In a further eight infected cattle, increases in permeability of vessels associated with serosal surfaces were demonstrated by labelling with either colloidal carbon or Evans blue. Intravenous injections of carbon provided both macroscopic and histological labelling of affected vessels. Evans blue appeared to be more sensitive than carbon but did not provide a histological marker of vascular permeability and provided labelling of tissues rather than individual vessels. The main sites of increased permeability were synovial, pericardial, thoracic and abdominal serosae.

Subcutaneous and pulmonary emphysema as complications of bovine ephemeral fever.

Subcutaneous and pulmonary emphysema was observed in some cattle on farms on which outbreaks of bovine ephemeral fever (BEF) occurred. BEF virus was isolated in baby hamsters from one of the cases and cattle were injected with blood from this animal. Although the experimental animals developed typical BEF symptoms, no signs of emphysema could be detected by clinical and pathological examinations. The histopathological changes in the skeletal muscle and synovial membranes of the natural case resembled those of BEF described by Basson, Pienaar & Van der Westhuizen (1970). The lumina of the terminal and respiratory bronchioles in the lungs were obliterated by cellular debris and the muscular portion of some of these bronchioles was necrotic. The possible pathogenesis of pulmonary emphysema is discussed.

Studies on the pathogenesis of bovine ephemeral fever.

A study of the pathogenesis of bovine ephemeral fever confirmed that the major clinical signs were fever lasting no more than 2 days, with increased respiratory rate, dyspnoea and some degree of lameness. Haematological observations revealed a neutrophilia with a left shift and a lymphopaenia at the time of peak clinical reaction. The net result was a slight leucopaenia on the day after this reaction. The most prominent pathological changes involved the lungs and synovial joints. Pulmonary emphysema and alveolar collapse with bronchiolitis, degenerative changes in synovial membranes and increased synovial fluid were observed. Specific fluorescence indicating the presence of BEF viral antigen could be detected at the time of peak clinical response in individual cells in the lungs, spleen and lymph nodes as well as neutrophils. Before and after the peak fever some fluorescence was seen in cells which appeared to be reticular cells in the lymph nodes. Viral isolation in mice could be made from blood, lungs, spleen and lymph nodes over a period of no more than 3 days. It is postulated that viral growth takes place mainly in the reticuloendothelial cells in the lungs, spleen and lymph nodes and not in vascular endothelium or lymphoid cells.

Ataxia and paralysis associated with bovine ephemeral fever infection.

Three adult cattle that had been ataxic for 5 to 7 months and a bull that had been paralysed for 24 days following bovine ephemeral fever infection were studied clinically and pathologically. Severe bilaterally symmetrical Wallerian degeneration was demonstrated in the spinal cords of all 4 cattle; in 3 animals an area of primary damage was present in the first cervical segment of the cord and in the other animal it was at the level of the lumbar cord. Pressure on the cord resulting from trauma was considered to be the most likely aetiology because of the similarity of the lesion to other syndromes causing pressure on the cord and the absence of the usual inflammatory changes seen with infectious agents.