Seroprevalence and risk factors for the presence of ruminant pestiviruses in the Dutch swine population

Swine can be infected with classical swine fever virus (CSFV), as well as ruminant pestiviruses: bovine viral diarrhoea virus (BVDV), and Border disease virus (BDV). Cross-reactions between pestiviruses occur, both regarding protective immunity and in diagnostic tests. The presence of BVDV and BDV in a swine population may thus affect the transmission of CSFV, but also the diagnosis of a CSFV infection. In this study, the seroprevalence against BVDV and BDV in two categories of swine, sows and finishing pigs, in the Netherlands was determined. Furthermore, several risk factors, associated with the presence of swine and ruminants on the same farm or in the immediate surroundings, were evaluated. In sows, the seroprevalence against BVDV was 2.5% on the animal level, and 11.0% on herd level. In finishing pigs these prevalences were 0.42% and 3.2%, respectively. Antibodies against BDV were found in three sows only. Risk factors, associated with a BVDV-seropositive status in breeding pigs, were the presence of cattle on the same premises and a high density of sheep and/or goats herds in a radius of 3 km. While BVDV and BDV hardly pose any threat to the swine population themselves, knowledge, and therefore regular monitoring, on the presence of these viruses in the swine population is important with respect to CSF eradication. It will allow for a better interpretation of diagnostic test results, both in terms of possible false positives and false negatives, but may also bring about additional measures or surveillance protocols in times of CSF outbreaks to avoid surprises caused by cross-reactivity with ruminant pestiviruses.