Bovine viral diarrhea viral infections in feeder calves with respiratory disease: Interactions with Pasteurella spp., parainfluenza-3 virus, and bovine respiratory syncytial virus

The prevalence of bovine viral diarrhea virus (BVDV) infections was determi ned in a group of stocker calves suffering from acute respiratory disease. The calves were assembled after purchase from Tennessee auctions and transp orted to western Texas. Of the 120 calves, 105 (87.5%) were treated for res piratory disease. Sixteen calves died during the study (13.3%). The calves received a modified live virus BHV-1 vaccine on day 0 of the study. During the study, approximately 5 wk in duration, sera from the cattle, collected at weekly intervals, were tested for BVDV by cell culture. Sera were also t ested for neutralizing antibodies to BVDV types 1 and 2, bovine herpesvirus -1 (BHV-1), parainfluenza-3 virus (PI-3V), and bovine respiratory syncytial Virus (BRSV). The lungs from the 16 calves that died during the study were collected and examined by histopathology, and lung homogenates were inocul ated onto cell cultures for virus isolation. There were no calves persisten tly infected with BVDV detected in the study, as no animals were viremic on day 0, nor were any animals viremic at the 2 subsequent serum collections. There were, however, 4 animals with BVDV type 1 noncytopathic (NCP) strain s in the sera from subsequent collections. Viruses were isolated from 9 lun gs: 7 with PI-3V, 1 with NCP BVDV type 1, and 1 with both BVHV-1 and BVDV. The predominant bacterial species isolated from these lungs was Pasteurella haemolytica serotype 1. There was serologic evidence of infection with BVD V types 1 and 2, PI-3V, and BRSV, as noted by seroconversion (greater than or equal to 4-fold rise in antibody titer) in day 0 to day 34 samples colle cted from the 104 survivors: 40/104 (38.5%) to BVDV type 1; 29/104 (27.9%) to BVDV type 2; 71/104 (68.3%) to PI-3V; and 81/104 (77.9%) to BRSV. In sev eral cases, the BVDV type 2 antibody titers may have been due to crossreact ing BVDV type 1 antibodies; however, in 7 calves the BVDV type 2 antibodies were higher, indicating BVDV type 2 infection. At the outset of the study, the 120 calves were at risk (susceptible to viral infections) on day 0 bec ause they were seronegative to the viruses: 98/120 (81.7%), < 1:4 to BVDV t ype 1; 104/120 (86.7%) < 1:4 to BVDV type 2; 86/120 (71.7%) < 1:4 to PI-3V; 87/120 (72.5%) < 1:4 to BRSV; and 111/120 (92.5%) < 1:10 to BHV-1. The res ults of this study indicate that BVDV types 1 and 2 are involved in acute r espiratory disease of calves with pneumonic pasteurellosis. The BVDV may be detected by virus isolation from sera and/or lung tissues and by serology. The BVDV infections occurred in conjunction with infections by other Virus es associated with respiratory disease, namely, PI-SV and BRSV. These other viruses may occur singly or in combination with each other. Also, the stud y indicates that purchased calves may be highly susceptible, after weaning, to infections by BHV-1, BVDV types 1 and 2, PI-3V, and BRSV early in the m arketing channel.