|Briggs, Robert - Bob|
Submitted to: Canadian Journal of Veterinary Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/29/2002
Publication Date: 7/1/2002
Citation: Fulton, R.W., Ridpath, J.F., Saliki, J.T., Briggs, R.E., Confer, A.W., Burge, L.J., Purdy, C.W., Loan, R.W., Duff, G.C., Payton, M.E. 2002. Bovine viral diarrhea virus (BVDV) 1b: predominant BVDV subtype in calves with respiratory disease. Canadian Journal of Veterinary Research. 66:181-190. Interpretive Summary: Infection with bovine viral diarrhea viruses (BVDV) is a source of major economic loss to U.S. cattle producers. Efforts to detect and prevent BVDV infection in cattle are hampered by the variations observed among different strains of BVDV. Based on the comparison of genetic material, BVDV can be divided into groups called genotypes. Genotypes represent the major branches of the BVDV family tree. These major branches are sometime made up of smaller branches (subgenotypes). It has been shown in earlier studies that the differences between the major branches of the BVDV tree are important. However, it is not known if the differences between the minor branches that make up a major branch are important. This study showed that one of the minor branches of the BVDV family tree (subgenotype BVDV1b) is associated much more frequently with respiratory disease in feedlot calves than viruses from the other minor branch (subgenotype BVDV1a). This finding may be significant because all the BVDV vaccines are based on viruses from subgenotype BVDV1a. The authors speculate that these vaccines may not do a good job protecting cattle against respiratory disease caused by viruses from the BVDV1b genotype.
Technical Abstract: The prevalence of bovine viral diarrhea virus (BVDV) infections was determined in 2 groups of stocker calves with acute respiratory disease. Both studies used calves assembled after purchase from auction markets by an order buyer and transported to feedyards, where they were held for approximately 30 d. In 1 study, the calves were mixed with fresh ranch calves from a single ranch. During the studies, at day 0 and at weekly intervals, blood was collected for viral antibody testing and virus isolation from peripheral blood leukocytes (PBLs), and nasal swabs were taken for virus isolation. Samples from sick calves were also collected. Serum was tested for antibodies to bovine herpesvirus-1 (BHV-1), BVDV1a, 1b, and 2, parainfluenza 3 virus (PI3V), and bovine respiratory syncytial virus (BRSV). The lungs from the calves that died during the studies were examined histopathologically, and viral and bacterial isolation was performed on lung homogenates. BVDV was isolated from calves in both studies; the predominant biotype was noncytopathic (NCP). Differential polymerase chain reaction (PCR) and nucleic acid sequencing showed the predominant subtype to be BVDV1b in both studies. In 1999, NCP BVDV1b was detected in numerous samples over time from 1 persistently infected calf; the calf did not seroconvert to BVDV1a or BVDV2. In both studies, BVDV was isolated from the serum, PBLs, and nasal swabs of the calves, and in the 1999 study, it was isolated from lung tissue at necropsy. BVDV was demonstrated serologically and by virus isolation to be a contributing factor in respiratory disease. It was isolated more frequently from sick calves than health calves, by both pen and total number of calves. BVDV1a and BVDV2 seroconversions were related to sickness in selected pens and total number of calves. In the 1999 study, BVDV-infected calves were treated longer than noninfected calves (5.643 vs 4.639 d; P=0.0902). There was a limited number of BVDV1a isolates and, with BVDV1b used in the virus neutralization test for antibodies in seroconverting calves' serum, BVDV1b titers were higher than BVDV1a titers. This study indicates that BVDV1 strains are involved in acute respiratory disease of calves with pneumonic Mannheimia haemolytica and Pasteurella multocida disease. The BVDV2 antibodies may be due to cross-reactions, as typing of the BVDV strains revealed BVDV1b or 1a but not BVDV2. The BVDV1b subtype has considerable implications, as, with 1 exception, all vaccines licensed in the United States contain BVDV1a, a strain with different antigenic properties. BVDV1b potentially could infect BVDV1a-vaccinated calves.