Submitted to: Archives of Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/11/2000
Publication Date: N/A
Interpretive Summary: Respiratory bovine coronavirus (RBVC) infection was associated for the first time with marketing stress induced acute bovine respiratory disease complex (BRDC). The light weight feeder calves (105) were purchased from TN auction markets, assembled in a TN order buyer barn (OBB), and moved to a TX research feedyard. Clinical signs of respiratory tract diseases and results of RBCV isolation assigned these cattle into 5 response groups. Response group 1 included 72 calves that exhibited clinical signs of respiratory tract disease, and were shedding RBCV on day 0, day 7 or both. Seven animals were randomly chosen from each shedding pattern for testing in this study. Response group 2 contained 5 test calves that secreted RBCV in nasal discharges without adverse respiratory signs. The 10 calves of response group 3 developed severe pneumonia, and died on days 7 to 11, and 9 that nasally shed RBCV were selected. Eighteen calves remained RBCV isolation-negative. Eleven of them were included in response group 4 because they had fever and other respiratory signs, while the remaining 7 calves (response group 5) remained clinically healthy during the 5-week investigation. Samples of 7 representative calves from response groups 4 and 5 were serologically analyzed. Based on our virus isolation results and the detected antibody levels, we concluded that most of these cattle became naturally infected with RBCV shortly before they were assembled at the OBB, and that virus spread was enhanced by stressful conditions during marketing and transport. Thus, RBCV is another important virus that contributes to BRDC. A RBCV vaccine needs to be developed.
Technical Abstract: Antibody responses against respiratory bovine coronavirus (RBCV) infections were monitored in cattle from the onset of a naturally occurring severe shipping fever (SF) epizootic to complete recovery of affected cattle or fatal out-comes. The infection with RBCV was detected in nasal secretions of 86 cattle, and 81 of them developed acute respiratory tract disease, including fatal pneumonia. Cattle nasally shedding RBCV at the beginning of the epizootic experienced characteristic primary immune responses with specific antibodies for hemagglutinin-esterase (HE) and spike (S) glycoproteins. Virus shedding in nasal secretions of the majority of the cattle ceased between days 7 and 14 with the appearance of HE- and S-specific antibodies. Nasal samples and lung tissues from 9 of the 10 fatal cases had high titers of RBCV, but these cattle had only IgM responses to RBCV infections. Cattle remaining negative in RBCV isolation tests entered this epizootic with antibodies against HE and S. Protection against respiratory tract disease was apparently associated with high level of opsonic and virus-neutralizing IgG2. The HE and S glycoproteins were recognized earliest by the bovine immune system while the N protein induced antibody responses during the later stage of initial infection and the early stage of reinfection. The membrane (M) glycoprotein was the least immunogenic of the major viral structural proteins.