Seroprevalence of pestivirus infections is low in Belgian small ruminant flocks and is significantly associated with the presence of cattle

Abstract

A study was implemented to estimate the pestivirus seroprevalence in sheep and goats in Belgium, to identify circulating species and to check for a potential association between seropositivity of small ruminants and presence of cattle in the same farm. It was based on the testing of serum samples and bulk tank milk samples (BTM) collected in sheep and goat flocks in 2018-2019 all over the country. 7460 serum samples collected from 410 flocks were tested by a commercial ELISA able to detect antibodies (Ab) against Border Disease Virus (BDV), and Bovine Viral Diarrhea Virus (BVDV). BTM samples (n = 144) were collected from dairy flocks in November 2019 and tested with the same Ab ELISA. ELISA positive serum samples were also tested by virus neutralization test (VNT) for neutralizing antibodies against BDV, BVDV-type1 and BVDV-type2. Virological tests (RT-PCR) were performed on pools of serum samples from pestivirus-exposed flocks with at least two seropositive animals and on all Antibody-positive BTM samples. Information about serum and milk samples (identification, test results, farm of origin and location, presence of cattle) were gathered in animal-level and farm-level databases. Based on this study, the apparent animal seroprevalence for pestiviruses in small ruminant flocks in Belgium in 2018 was estimated to be 0.87 % (95 % C.I. [0.68 %-1.11 %]). The prevalence of flocks exposed to pestivirus (i.e. with at least one seropositive animal) was estimated to be 8.5 % (95 % C.I. [6.4 % - 11.6 %]). In exposed flocks, the average within-flock seroprevalence was 9.9 %. In dairy sheep and goats, the estimated proportion of exposed flocks in 2019, based on the detection of pestivirus antibodies in the bulk tank milk, was 9.7 % [5.9 %-15.7 %]. All PCR tests were negative, indicating the likely absence of active pestivirus circulation in these flocks. Although the observed pestivirus seroprevalence was found to be low in Belgian small ruminants, this study also showed, based on VNT results, that they are exposed to several pestivirus species: BDV, BVDV-1 and BVDV-2. 22.4 % of the farms included in the serological survey were holding both a small ruminant flock and a cattle herd, hence with a potential risk of contact between the two species. There was a significant positive association between pestivirus seropositivity in the sheep/goat flocks and the presence of a cattle herd in the same farm (OR = 2.42 (95 %C.I. [1.18-4.94]) but this association was not found for Ab-positive BTM in dairy flocks.

Keywords: Belgium; Border disease virus; Bovine viral diarrhea virus; Pestivirus; Seroprevalence; Small ruminants.