Clinical, pathological and antigenic aspects of bovine viral diarrhea virus (BVDV) type 2 isolates identified in Brazil

Nucleotide sequencing and phylogenetic analysis of Brazilian bovine viral d iarrhea virus (BVDV) field isolates identified four viruses belonging to th e genotype 2. Comparison of 5' UTR sequences from these isolates to those o f North American BVDV type 2 revealed genomic variations that correlated wi th the geographic origins of the isolates. Two of the Brazilian type 2 viru ses were isolated from clinical cases of gastroenteric/respiratory disease and two were isolated from healthy bovine fetuses. The clinical cases affec ted young animals (8- and 18-months-old) and were characterized by diarrhea , respiratory signs, extensive oral and digestive tract erosions, conjuncti val and vulvar congestion, occasional digestive bleeding and vulvar and hea rt petechial hemorrhage. Antigenic analysis of these isolates with a panel of 10 monoclonal antibodies revealed marked antigenic differences in the ma jor envelope glycoprotein, gp53/E2, compared to standard laboratory and vac cine BVDV strains. In addition, virus-specific antisera raised to Brazilian BVDV type 2 viruses displayed very low serological cross-reactivity with s tandard BVDV type 1 strains. Differences up to 64-fold in cross-neutralizat ion titers were observed between BVDV type 1 and Brazilian BVDV type 2 isol ates. The identification of BVDV type 2 among Brazilian cattle may have imp ortant implications for epidemiological studies, diagnostic and immunizatio n strategies. Furthermore, the low neutralizing activity of BVDV type 1 ant isera against the recently identified Brazilian BVDV type 2 isolates raises the question about the degree of protection conferred by BVDV vaccines, mo st of them based on a single type I strain. (C) 2000 Elsevier Science B.V. All rights reserved.