Clinical response of cattle to experimental infection with bovine ephemeral fever virus.

As part of a study of the pathology and pathogenesis of bovine ephemeral fever virus infection 44 cattle were infected by the intravenous injection of virulent virus. Thirty-eight animals responded clinically and detailed haematological and serological data were obtained from 10 of them. Inappetence was the only clinical sign observed before the onset of fever. The temperature response was characteristically biphasic, with the second peak occurring 12 to 24 hours after the first. The only consistent haematological response was an increase in the numbers of circulating neutrophils with a concurrent decline in the numbers of mononuclear leucocytes. There were no detectable changes in plasma or blood volume, packed cell volume, red cell count, haemoglobin concentration, serum calcium, magnesium, phosphorus and creatinine concentrations, or aspartate aminotransferase activity. Viraemia was demonstrated on either the first or second day of clinical disease and lasted for at most 48 hours. Low levels of neutralising antibody could be detected within one or two days after the cessation of viraemia. Six antibody-free animals did not respond clinically to injection with virulent virus, and did not develop detectable viraemia or a serum neutralising antibody response.