Significant Impact of Schmallenberg Virus in Three Ruminant Farms: A Laboratory Experience

Schmallenberg virus (SBV) is endemic in Europe and other parts of the world and represents an underestimated and underdiagnosed cause of abortion and economic losses for livestock farms. In the present study, we evaluated SBV's impact on three ruminant farms, in particular, two dairy cattle farms with reproductive problems (including abortions, stillbirths, and malformations) and a clinically healthy buffalo farm involved in oocyte collection through ovum pick-up (OPU) for in vitro embryo production and commercial sale. All sampled animals were subjected to serological assays against the main infectious agents responsible for reproductive disorders in ruminants: SBV, bluetongue virus (BTV), Coxiella burnetii (C. burnetii), bovine herpesvirus type 1 (BHV-1), bovine viral diarrhea virus (BVDV), and Brucella abortus (B. abortus). The first herd with reproductive disorders had a high (78%) seroprevalence for SBV (considered to be the cause of reproductive problems), while the prevalence observed for BTV was modest (16.7%). Although free from B. abortus, the second dairy farm had only a few animals that were seropositive for C. burnetii and BTV (1/22 and 2/22, respectively), but a prevalence of 72.7% for SBV. The buffalo farm had several animals seropositive for C. burnetii (9/52), BTV (10/52), and SBV (12/52). Almost half of the sampled animals were exposed to at least one pathogen (26/52). Seropositive animals were excluded from oocyte collection in compliance with regulatory health requirements. One month later, seronegative animals were retested, revealing the seroconversion of another animal for SBV, which was also excluded. This study has described, through seroprevalence testing, the direct impact of SBV on livestock (clinical impact) and how it affects the selection of animals for the trade of genetic material (indirect impact).