Submitted to: American Association of Veterinary Laboratory Diagnosticians
Publication Type: Abstract Only
Publication Acceptance Date: July 28, 2010
Publication Date: November 10, 2010
Citation: Ridpath, J.F., Lovell, G., Neill, J.D., Hairgrove, T.B., Velayudhan, B., Mock, R. 2010. Change in Predominance of Bovine Viral Diarrhea Virus Subgenotypes Among Samples Submitted to a Diagnostic Laboratory Over a 20-Year Time Span [abstract]. American Association of Veterinary Laboratory Diagnosticians. p. 102. Technical Abstract: While the causative agent of bovine viral diarrhea was initially categorized as one species, phylogenetic analysis revealed that these viruses belong to two different species, bovine viral diarrhea virus type 1 (BVDV1) and BVDV2. Further analysis led to the recognition of multiple subgenotypes within both species (BVDV1a through BVDV1k and BVDV2a and b). From the first characterization of noncytopathic BVDV in 1957 until the 1980s, BVDV isolations reported in the literature belonged exclusively to the BVDV1 species. Most lab reference strains and vaccines strains in use from the 1960s to the 1990s belonged to the BVDV1a subgenotype. In 1994 it was recognized that a syndrome known as hemorrhagic disease resulted from infection with a genetically distinct group of pestiviruses, BVDV2. Recognition of antigenic differences between BVDV1 and BVDV2 strains led to the development of bivalent BVDV vaccines, in the 1990s, that contained antigens derived from both BVDV1a and BVDV2a strains. Surveys conducted between 1994 and 2008, report three BVDV subgenotypes circulating among cattle in the United States; BVDV1a, BVDV1b, and BVDV2a. The average percent prevalence of BVDV1a, BVDV1b, and BVDV2a strains reported in surveys prior to 2001 were 21%, 43%, and 36%, respectively. Surveys conducted on viruses isolated after 2001 reported decreasing percentages of BVDV1a and BVDV2a strains with BVDV1b strains accounting for 75% to 100% of samples. Comparison of these surveys is confounded by differences in geographic location, method of collection, and type of sample used in survey. The purpose of this study was to determine if there was a shift in the prevalence of BVDV subgenotypes in the same geographic region in samples collected by the same laboratory over time. To this end, submissions to the Texas Veterinary Medical Diagnostic Laboratory, Amarillo, Texas, were analyzed over a 20-year time span. The same methods of sample collection, storage, and virus isolation were used over the span of the study. BVDV strains isolated in years 1988, 1998, and 2008 were genotyped and prevalence of BVDV1a, BVDV1b, and BVDV2a strains were determined. A total of 155 strains were genotyped based on comparison of sequences from the 5’ untranslated region (5’ UTR). Of these strains, 66 were isolated in 1988, 44 in 1998, and 44 in 2008. Of the 1988 strains, two were re-isolations of BVDV1a vaccine strains and one sample had a mixture of BVDV strains. Of the remaining strains, 51% were BVDV1a strains, 41% were BVDV1b strains, and 8% were BVDV2a strains. Four of the 44 strains isolated in 1998 were re-isolations of BVDV1a vaccine strains. Of the remaining strains, 31% were BVDV1a strains, 53% were BVDV1b strains, and 16% were BVDV2a strains. Of the 44 strains isolated in 2008, 12 were re-isolations of BVDV1a vaccine strains. Of the remaining strains, 18% were BVDV1a, 61% were BVDV1b, and 21% were BVDV2a. The proportion of field strains identified as BVDV1a showed a steady decrease over the observed time span. The preponderance of BVDV1a strains among the earliest reported BVDV isolations, also suggests that BVDV1a strains might have been more prevalent in the 1960s than they are now. While the reason for the decline in BVDV1a strains cannot be established from this study, it should be noted that vaccines based on BVDV1a antigens have been available since the 1960s, while vaccine containing BVDV2a antigens have only been available since the 1990s. At present there are very few vaccines that contain BVDV1b antigens.