|Briggs, Robert - Bob|
Submitted to: Journal of Clinical Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/29/2000
Publication Date: N/A
Interpretive Summary: Pasteurella haemolytica A1 (PhA1) is the cause of most cases of acute fibrinous bronchopneumonia associated with bovine respiratory disease (BRD) in stocker/feeder calves, which cost the industry more than $750 million dollars per year. The disease usually develops after calves are marketed and transported and, often, after the calves have contracted viral respiratory tract infections. The known important viruses associated with acute BRD are infectious bovine rhinotracheitis virus (IBR), parainfluenza-3 virus (PI-3), respiratory syncytial virus (RSV), and bovine viral diarrhea virus (BVDV). We recently discovered a new virus, respiratory bovine coronavirus (RBCV) associated with acute BRD in Tennessee calves shipped on two different years to a feedyard located in Bushland, TX. This virus was excreted in nasal mucus and was found in the lungs of calves dying of BRD. The coronavirus and PhA1 infectious loads were sequentially quantified over time and their antibody titers were also compared over time to clinically normal and RBCV isolation-negative calves. The discovery of a new respiratory virus (coronavirus) is extremely important to the feeder calf industry, as no protective vaccines are available, and the coronavirus appears to be very effective in making the bovine respiratory tract susceptible to the PhA1 bacteria which kills calves or induced dreaded expensive chronic pneumonias.
Technical Abstract: Respiratory tract infections with viruses and Pasteurella spp. were determined sequentially among 26 cattle that died during two severe epizootics of shipping fever pneumonia. Nasal swab and serum samples were collected prior to onset of the epizootics, during disease progression, and after death, when necropsies were performed and lung samples were collected. Eighteen normal control cattle also were sampled at the beginning of the epizootics as well as at weekly intervals for 4 weeks. Respiratory bovine coronaviruses (RBCV) were isolated from nasal secretions of 21 and 25 cattle before and after transport. Two and 17 cattle nasally shed Pasteurella spp. before and after transport, respectively. RBCV were isolated at titers of 1 X 10**3 to 1.2 X 10**7 PFU per g of lung tissue from 18 cattle that died within 7 days of the epizootics, but not from the lungs of the remaining cattle that died on days 9 to 36. Twenty-five of the e26 lung samples were positive for Pasteurella spp., and their CFU ranged between 4.0 X 10**5 and 23 X 10**9 per g. Acute and subacute exudative, necrotizing lobar pneumonia characterized the lung lesions of these cattle typical of pneumonic pasteurellosis, but other lung lobules had histological changes consisting of bronchiolitis and alveolitis typical of virus-induced changes. These cattle were immunologically naive to both infectious agents at the onset of the epizootics, but those that died after day 7 had rising antibody titers against RBCV and Pasteurella haemolytica. In contrast, the 18 clinically normal and RBCV isolation-negative cattle had high hemagglutinin inhibition antibody titers to RBCV from the beginning, while their antibody responses to P. haemolytica antigens were delayed. These viruses were previously not recognized as a causative agent.