Submitted to: Veterinary Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/24/2002
Publication Date: 11/1/2002
Citation: Evermann, J.F., Ridpath, J.F. Clinical and epidemiologic observations of bovine viral diarrhea virus in the northwestern United States. Veterinary Microbiology. 2002. v. 89. p. 129-139. Interpretive Summary: Infection with bovine viral diarrhea viruses (BVDV) are a source of major economic loss to U.S. cattle producers. In this study we analyzed cases of clinical disease in cattle from which BVDV was isolated. These cases were submitted to a diagnostic laboratory in the northwestern United States between 1980 and 2000. In this 20-year time frame there was a shift in the age of the animal at infection and the type of disease resulting from infection. The relationship between the type of disease, the age of the animal and the genetic relationships between BVDVs were also examined. It was found that different branches of the BVDV "family tree" tend to infect animals at different stages in life. These studies suggest that animals are most vulnerable to BVDV infections while they are fetuses (in utero) and at 6 months of age. Animals may become infected in utero because the mother does not have adequate antibodies to fight off a BVDV infection or because the mother's immune system does not function as effectively during pregnancy. Animals may be vulnerable to BVDV infections at 6 months because this is the age at which antibody protection received from the mother (passive antibodies) declines and disappears. Vaccines must be developed that protect the fetus from infection. In addition, vaccine programs must be designed to immunize cows before breeding and calves as passive antibodies decline and disappear.
Technical Abstract: Retrospective analyses of cases from which bovine viral diarrhea virus (BVDV) was isolated from 1980-2000 were conducted. These cases originated from the northwestern United States and included beef and dairy cattle. The results indicated that there was a shift in diseases associated with BVDV infection and in the animal's age at onset of disease. Comparative results from the 1980 data indicated a low fetal infection rate (<5%), followed by steady increases of clinical cases and peaking at 6 months (30%). By 2000, the shift of BVDV cases was noticeable and indicated a biphasic incidence of disease. The first phase was fetal infections, which increased to >25%, followed by a second phase at 6 months (>35%). Phylogenetic analysis was conducted on isolates from 1999-2000 (n = 53). There were representatives from the two genotypes, BVDV1 and BVDV2, as well as subgenotypes BVDV1a and BVDV1b. The types were further correlated with the clinical manifestations. The results indicated that BVDVs were distributed throughout the clinical spectrum of disease, with BVDV2 representing the greatest frequency of isolation, and the greatest association with abortion-open cows. When the BVDV genotypes and subgenotypes were categorized into early (<90 days gestation) versus late (>90 days gestation) fetal infections, there was an inverse relationship noted. It was observed that BVDV1a was associated least with early infection (14%) and most with late infections (86%). BVDV1b was intermediate, followed by BVDV2 which was associated more with early infections (45%) and less with late infections (55%) when compared with BVDV1a and BVDV1b.