Benefit of Bovine Viral Diarrhoea (BVD) Eradication in Cattle on Pestivirus Seroprevalence in Sheep

Abstract

Bovine viral diarrhoea virus (BVDV) and Border disease virus (BDV) are closely related pestiviruses of cattle and sheep, respectively. Both viruses may be transmitted between either species, but control programs are restricted to BVDV in cattle. In 2008, a program to eradicate bovine viral diarrhoea (BVD) in cattle was started in Switzerland. As vaccination is prohibited, the cattle population is now widely naïve to pestivirus infections. In a recent study, we determined that nearly 10% of cattle are positive for antibodies to BDV. Here, we show that despite this regular transmission of BDV from small ruminants to cattle, we could only identify 25 cattle that were persistently infected with BDV during the last 12 years of the eradication program. In addition, by determining the BVDV and BDV seroprevalence in sheep in Central Switzerland before and after the start of the eradication, we provide evidence that BVDV is transmitted from cattle to sheep, and that the BVDV seroprevalence in sheep significantly decreased after its eradication in cattle. While BDV remains endemic in sheep, the population thus profited at least partially from BVD eradication in cattle. Importantly, on a national level, BVD eradication does not appear to be generally derailed by the presence of pestiviruses in sheep. However, with every single virus-positive cow, it is necessary to consider small ruminants as a potential source of infection, resulting in costly but essential investigations in the final stages of the eradication program.

Keywords: Switzerland; border disease virus (BDV); bovine viral diarrhoea virus (BVDV); eradication; persistent infection; pestivirus; seroprevalence; virus transmission.

Figure 1

Geographic distribution of the place of birth of cattle persistently infected with BDV with the subgenotype BD-3 in green, BDswiss-A in red and BDswiss-B in yellow. The location of the farm where the persistently infected sheep (mm1455) was identified is shown in purple. The corresponding cantons were labelled as Bern (BE), Luzern (LU), Nidwalden (NW), Obwalden (OW), Uri (UR), Schwyz (SZ), Zug (ZG), St. Gallen (SG), Graubünden (GR), and Thurgau (TG). The cantons of Central Switzerland are stained in blue.

Figure 2

Phylogenetic analysis of nucleotide sequences encompassing the 5'-UTR of the pestiviral RNA genome. All the major sub-genotypes of pestiviruses described in Switzerland are included in the tree, i.e., BDV-3 and BDswiss (BDV-8) with samples from this study, representative samples of BVDV-1b, -1e, -1h, and -1k (21), strains of atypical porcine pestiviruses found in domestic pigs in Switzerland (29), and strains of classical swine fever virus isolated in Switzerland in the last outbreak in wild boars around the year 2000 (31). The evolutionary history was inferred using the neighbour-joining method. The genetic analysis was calculated, and the figure prepared as described in Supplementary Table 7. The numbers close to the branches represent the values (%) of 1,000 bootstrap replicates, and only values ≥99 are indicated. Line lengths are proportional to genetic distance and are in the units of the number of base differences per sequence, as indicated by the scale bar.