Seroepidemiological Investigation of Ruminant Pestivirus in Pig and Cattle Population in Ibaraki Prefecture, Japan

Abstract

Ruminant pestiviruses (RPV) include bovine viral diarrhea virus (BVDV) and border disease virus (BDV). Owing to the cross-reactivity between these viruses and classical swine fever virus (CSFV) antibodies, infection of pigs with RPV may cause problems in the serological diagnosis of classical swine fever (CSF). We conducted a seroepidemiological investigation aiming to elucidate the infection status of RPV in pig and cattle populations in Ibaraki Prefecture using samples collected prior to the CSF outbreak in 2018. Of 226 pig farms, 4 (1.8%) tested positive for BVDV antibodies by ELISA, and the individual-level prevalence was 0.25% (12/4,881). Viral neutralization tests conducted for the four farms resulted in the detection of BVDV1 and BDV antibodies in three farms and one farm, respectively. Among 377 dairy farms, 44 persistently infected (PI) cattle were identified in 20 farms (5.3%). The BVDV-1b subgenotype accounted for 75% (33/44) of these PI cattle. Furthermore, a BVDV antibody-positive pig farm was located geographically close to a PI cattle farm. The current results suggest that PI cattle in dairy farms are a source of infection in pig farms where BVDV antibodies are detected. Therefore, determination of BVDV and BDV infection status in ruminants and prevention of RPV infection in pigs are essential for the prompt and accurate diagnosis of CSF. Furthermore, once antibodies against RPV are detected in a pig farm, additional investigation using viral neutralization tests against CSFV and RPV is paramount.